bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of aggregation on the redox chemistry of humic substances
Authors: Palmer Noel E. , von Wandruszka Ray
Published: April 2009

Environmental context. The ability of humic substances (decaying plant and animal matter) to partake in redox reactions in the environment depends on the extent to which the various humic polymers aggregate in solution to form larger particles. This aggregation, in turn, is predicated on the solution conditions, especially ionic strength, the pH, and the types of cations present. Abstract. Aggregation and conformation play an important role in the aqueous redox chemistry of humic substances (HS). The reduction potentials of dissolved humic and fulvic acids vary with pH, ionic strength, and type of humate used, and depending on the solution conditions, they can abiotically reduce various species. Changes in HS reduction potential ranged from 60 to 140 mV on addition of divalent cations, whereas no significant changes were observed with equivalent additions of monovalent cations. Dynamic light scattering measurements showed that this behaviour paralleled the size changes obtained with humic aggregates under the same conditions. The effect was more pronounced at higher pH, where divalent cations caused a significant decrease in the average hydrodynamic radius, whereas monovalent cations did not. At pH 4, neither mono- nor divalent cations substantially affected aggregate sizes. Quinoid moieties, which are known to play an important role in the redox chemistry of HS, displayed fluorescence excitation–emission matrices with features related to changes in the reduction potential of HS. An increase in the reduction potential (Eh) induced by the addition of Ca2+, for instance, caused a red shift in the excitation–emission matrix maximum.
Photodegradation of nonylphenol polyethoxylates in aqueous solution
Authors: Wang Lei , Sun Hongwen , Wu Yinghong , Huang Guolan , Dai Shugui
Published: April 2009

Environmental context. Nonylphenol polyethoxylates (NPEOs) are widely used non-ionic surfactants, and they cause environmental concern because some metabolites of NPEOs possess endocrine-disrupting activities. Photodegradation is an important pathway for NPEOs degradation, and different degradation products may lead to different environmental risks. The present paper looks at the kinetics and pathways of NPEO photodegradation in aqueous solutions, focussing on the effects of humic acid, H2O2, and FeIII. We found that the presence of different chemicals led to different degradation pathways, and a new mechanism is proposed.
Abstract. To further elucidate the mechanism of photoinduced degradation of nonylphenol polyethoxylates (NPEOs) in aqueous environments, two different light systems, UVA and simulated sunlight, were used, and the effects of humic acid, H2O2, and FeIII were investigated. The 96-h degradation efficiencies of NPEOs in pure water solution were found to be 36.6 and 22.6% under UVA and SSL irradiation respectively. The presence of humic acid and FeIII in solution increased the photodegradation efficiency of NPEOs to different extents. The proportion of short-chain NPEOs in the NPEOn mixture was found to increase significantly in the solution containing FeIII, whereas this phenomenon was not observed in pure water and solutions containing H2O2 or humic acid. The result of NPEO3 photodegradation experiments indicated that FeIII in solution led to an ethoxylate-reduction pathway. Dicarboxylated formate ethoxylates were proposed as the intermediate products of NPEO photodegradation through an oxidative pathway based on the analytical results of liquid chromatography–electrospray ionisation–mass spectrometry and tandem mass spectrometry. Different mechanisms of NPEO photodegradation were elucidated.
Antimony uptake by different plant species from nutrient solution, agar and soil
Authors: Tschan Martin , Robinson Brett H. , Nodari Matteo , Schulin Rainer
Published: April 2009

Environmental context. Because of its many industrial and other uses, antimony (Sb) is increasingly emitted into the environment through human activities. We studied the uptake of Sb by crop plants from three different substrates: hydroponic nutrient solutions, agar medium, and potting soil. The uptake of Sb increased linearly with Sb in solution or soluble Sb in soil over a wide range of concentrations until it was limited by toxicity. Antimony was much less toxic than its sister element arsenic compared on a molar basis. The results suggest that Sb may be accumulated by some crop plants on heavily contaminated soils at concentrations that may pose a health risk to humans and animals. Abstract. We investigated the uptake of antimonate from nutrient solutions, agar and soil by various cultivated plants, including Indian mustard (Brassica juncea (L.) Czern), sunflower (Helianthus annuus L.), perennial ryegrass (Lolium perenne L.), clover (Trifolium pratense L.), wheat (Triticum aestivum L.) and maize (Zea mays L.). Antimony uptake did not differ between the three growth media. In all tested plants, the shoot Sb concentration was proportional to Sb in solution or soluble Sb in soil, until toxicity eventually limited growth. At a given Sb concentration in the growth medium, Sb accumulation differed between plant species by up to an order of magnitude. Clover grown in agar containing 160 mg L–1 Sb in solution accumulated 2151 mg kg–1 Sb (dry weight) in the shoots. Maize had the lowest accumulation. In maize and sunflower, most Sb accumulated in the leaves. The results indicate that antimony may accumulate in the edible parts of crop plants grown on heavily contaminated soils at concentrations that may pose a health risk to humans and animals.
Clarification of the predominant emission sources of antimony in airborne particulate matter and estimation of their effects on the atmosphere in Japan
Authors: Iijima Akihiro , Sato Keiichi , Fujitani Yuji , Fujimori Eiji , Saito Yoshinori , Tanabe Kiyoshi , Ohara Toshimasa , Kozawa Kunihisa , Furuta Naoki
Published: April 2009

Environmental context. The remarkable enrichment of potentially toxic antimony (Sb) in inhalable airborne particulate matter has become of great environmental concern among recent air pollution issues. The present study clarifies the predominant sources of Sb by focusing on the similarities in elemental composition, particle size distributions, and microscopic images found in ambient airborne particles and several potential sources. We identify automotive brake abrasion dust and fly ash emitted from waste incineration as dominant sources of atmospheric Sb in Japan. These results will contribute towards an in-depth understanding of the cycles and fates of Sb in the environment.
Abstract. By focusing on the similarities in elemental composition, particle size distributions of elemental concentrations, and microscopic images between ambient airborne particulate matter (APM) and several potential sources, we discuss the predominant sources of antimony (Sb) in APM in Japan. The distribution of Sb concentration in size-classified ambient APM showed a characteristic bimodal profile in which peaks were found in coarse (3.6–5.2 μm) and fine (0.5–0.7 μm) fractions. Elemental ratios, particle sizes, and microscopic images observed in the coarse APM fractions were found to be in good agreement with those of brake abrasion dust. However, in the fine APM fractions, fly ash originating from waste incineration was identified as the most probable source of Sb. Chemical mass balance analysis was performed to determine the effects of the emission sources of Sb, and it was revealed that brake abrasion dust and waste fly ash were the dominant sources of Sb in the coarser and the finer fractions of APM, respectively. The present study provides important clues to understanding the cycles and fates of Sb in the environment.
Antimony in the soil - plant system - a review
Authors: Tschan Martin , Robinson Brett H. , Schulin Rainer
Published: April 2009

Environmental context. Soil contamination by antimony (Sb) has become an environmental problem of much concern in recent years, because increasing mining and industrial use has led to widespread soil contamination by this biologically unessential, but potentially carcinogenic element. We reviewed the available literature and found that Sb is generally taken up by terrestrial plants in proportion to the concentration of soluble Sb in soil over a concentration range covering five or more orders of magnitude, a finding that is relevant in particular for the assessment of environmental and health risks arising from Sb-contaminated soils. But very little is known about the mechanisms of Sb uptake by plants. Abstract. Soil contamination by antimony (Sb) due to human activities has considerably increased in the recent past. We reviewed the available literature on Sb uptake by plants and toxicity risks arising from soil contamination by Sb and found that Sb is generally taken up by terrestrial plants in proportion to the concentration of soluble Sb in soil over a concentration range covering five or more orders of magnitude. However, very little is known about the mechanisms of Sb uptake by plants. Also the deposition of resuspended soil particles on the surfaces of aerial plant surfaces can result in high plant Sb concentration in the vicinity of Sb-contaminated sites. Although soil pollution by Sb may be rarely so severe as to cause toxicity problems to humans or animals consuming plants or food derived from plants grown on Sb-contaminated sites, such risks may arise under worst-case conditions.
Antimony in the environment: knowns and unknowns
Authors: Filella Montserrat , Williams Peter A. , Belzile Nelson
Published: April 2009

Environmental context. Antimony first attracted public attention in the mid-1990s amid claims that it was involved in Sudden Infant Death Syndrome. A substantial number of papers have now been published on the element and its behaviour in the natural environment. However, many key aspects of the environmental chemistry of antimony remain poorly understood. These include critical areas such as its ecotoxicology, its global cycling through different environmental compartments, and what chemical form it takes in different environments. More focussed research would help the situation. The present review highlights several areas of environmental antimony chemistry that urgently need to be addressed. Abstract. The objective of the present article is to present a critical overview of issues related to the current state of knowledge on the behaviour of antimony in the environment. It makes no attempt to systematically review all published data. However, it does provide a list of the main published reviews on antimony and identifies subjects where systematic reviews are needed. Areas where our knowledge is strong – and the corresponding gaps – in subjects ranging from total concentrations and speciation in the various environmental compartments, to ecotoxicity, to cycling between compartments, are discussed, along with the underlying research. Determining total antimony no longer poses a problem for most environmental samples but speciation measurements remain challenging throughout the process, from sampling to analysis. This means that the analytical tools still need to be improved but experience shows that, to be useful in practice, this should be directly driven by the requirements of laboratory and field measurements. Many different issues can be identified where further research is required, both in the laboratory and in the field, the most urgently needed studies probably being: (i) long-term spatial and temporal studies in the different environmental compartments in order to collect the data needed to establish a global biogeochemical cycle; (ii) laboratory studies of antimony interactions with potential natural binders; (iii) reliable ecotoxicological studies.
Attentional capture by object appearance and disappearance
Authors: Cole Geoff G. , Kuhn Gustav
Published: April 2009

In two experiments we examined whether the appearance of a new object has attentional priority over disappearance. Previous failures to show differences are possibly due to onsets and offsets always being presented as a sole visual transient. Rather than presenting each alone, we presented onset and offset singletons simultaneously with a display-wide luminance transient in order to force each to compete with other visual events. Results from Experiment 1 showed that targets associated with onsets accrued a reaction time benefit whilst targets associated with offsets did not. Experiment 2 showed that onsets attracted attention even when observers were attentionally set to look for offset. By contrast, offsets needed a relevant attentional set in order to attract attention. We argue that the appearance of an object has attentional priority over disappearance.
Characterization of four plasmids harboured in a Lactobacillus brevis strain encoding a novel bacteriocin, brevicin 925A, and construction of a shuttle vector for lactic acid bacteria and Escherichia coli
Authors: Wada Takaomi , Noda Masafumi , Kashiwabara Fumi , Jeon Hyung Joon , Shirakawa Ayano , Yabu Hironori , Matoba Yasuyuki , Kumagai Takanori , Sugiyama Masanori
Published: April 2009

In this study we isolated over 250 lactic acid bacteria (LAB) candidates from fruit, flowers, vegetables and a fermented food to generate an LAB library. One strain, designated 925A, isolated from kimchi (a traditional Korean fermented dish made from Chinese cabbage) produced a novel type of bacteriocin, brevicin 925A, which is effective against certain LAB, including strains ofLactobacillus,Enterococcus,Streptococcus,BacillusandListeria. Strain 925A, identified asLactobacillus brevis, harboured at least four plasmids and we determined the entire nucleotide sequence of each one. The four plasmids were designated pLB925A01–04, and have molecular sizes of 1815, 3524, 8881 and 65 037 bp, respectively. We obtained bacteriocin non-producing derivatives by treatment of strain 925A with novobiocin. All of these derivatives, which were susceptible to their own antibacterial product, lost the largest plasmid, pLB925A04, suggesting that the genes for bacteriocin biosynthesis (breBandbreC) and immunity (breE) are located on pLB925A04. The partial amino acid sequence of purified brevicin 925A and sequence analysis of pLB925A04 showed thatbreBis the structural gene for brevicin 925A. We constructed a shuttle vector (pLES003, 6134 bp) that can replicate in bothEscherichia coliand LAB such asLactobacillus plantarum,Lb. brevis,Lactobacillus helveticus,Lactobacillus hilgardiiandEnterococcus hirae. To determine the function of genebreE, which displays no significant similarity to any other sequences in theblastsearch database, the gene was inserted into pLES003. A pLB925A04-cured derivative transformed with pLES003 carryingbreEacquired immunity to brevicin 925A, suggesting thatbreEencodes an immunity protein.
Multiple acquisitions of CTX-M plasmids in the rare D2 genotype of Escherichia coli provide evidence for convergent evolution
Authors: Deschamps Catherine , Clermont Olivier , Hipeaux Marie Claire , Arlet Guillaume , Denamur Erick , Branger Catherine
Published: April 2009

Over the last decade, CTX-M enzymes have become the most prevalent extended-spectrumβ-lactamases (ESBLs) worldwide, mostly inEscherichia coli, causing a major health problem. An epidemiological relationship has been established between a rare genotype ofE. coli, the D2genotype, and the presence of CTX-M genes. We investigated this striking association by exploring the genetic backgrounds of 18 D2genotype CTX-M-producing strains and of the plasmids encoding CTX-M enzymes. The 18 strains had different genetic backgrounds, as assessed by multilocus sequence and O typing, and were associated with various plasmids bearing diverse CTX-M genes. The region encompassing the genetic marker of the D2genotype (TSPE4.C2) was not correlated with the presence of CTX-M genes. CTX-M-producing D2strains had far fewer virulence factors than a control group of 8 non-ESBL-producing D2strains, and an inverse relationship was found between the number of co-resistances associated with the CTX-M gene and the number of virulence factors found in the strain. These findings provide evidence for multiple acquisitions of plasmids carrying CTX-M genes in different D2genotype strains. They strongly suggest that convergent evolution has occurred, and indicate that there has been selection for the association of a specific genetic background of the strain and the CTX-M gene. This fine-tuning of the relationship between the D2genotype and CTX-M genes presumably increases the fitness of the strain, indicating a role for the host cell in the acquisition and dissemination of CTX-M genes.
A permease encoded by STL1 is required for active glycerol uptake by Candida albicans
Authors: Kayingo Gerald , Martins António , Andrie Rachael , Neves Luisa , Lucas Cândida , Wong Brian
Published: April 2009

Candida albicansaccumulates large amounts of the polyols glycerol andd-arabitol when the cells are exposed to physiological conditions relevant to stress and virulence in animals. Intracellular concentrations of glycerol are determined by rates of glycerol production and catabolism and of glycerol uptake and efflux through the plasma membrane. We and others have studied glycerol production inC. albicans, but glycerol uptake byC. albicanshas not been studied. In the present study, we found that [14C]glycerol uptake byC. albicansSC5314 was (i) accumulative; (ii) dependent on proton-motive force; (iii) unaffected by carbon source; and (iv) unaffected by large molar excesses ofd-arabitol or other polyols. The respectiveKmandVmaxvalues were 2.1 mM and 460 μmol h−1(g dry wt)−1in glucose medium and 2.6 mM and 268 μmol h−1(g dry wt)−1in glycerol medium. To identify theC. albicansglycerol uptake protein(s), we cloned theC. albicanshomologues of theSaccharomyces cerevisiaegenesGUP1andSTL1, both of which are known to be involved in glycerol transport. When multicopy plasmids encodingC. albicans STL1,C. albicans STL2andC. albicans GUP1were introduced into the correspondingS. cerevisiaenull mutants, the transformants all acquired the ability to grow on minimal glycerol medium; however, onlyS. cerevisiae stl1null mutants transformed withC. albicans STL1actively took up extracellular [14C]glycerol. When both chromosomal alleles ofC. albicans STL1were deleted fromC. albicansBWP17, the resultingstl1null mutants grew poorly on minimal glycerol medium, and their ability to transport [14C]glycerol into the cell was markedly reduced. In contrast, deletion of both chromosomal alleles ofC. albicans STL2or ofC. albicans GUP1had no significant effects on [14C]glycerol uptake or the ability to grow on minimal glycerol medium. Northern blot analysis indicated thatC. albicans STL1was expressed in both glucose and glycerol media, conditions under which we detected wild-type active glycerol uptake. Furthermore,STL1was highly expressed in salt-stressed cells; however, thestl1null mutant was no more sensitive to salt stress than wild-type controls. We also detected high levels ofSTL2expression in glycerol-grown cells, even though deletion of this gene did not influence glycerol uptake activity in glycerol-grown cells. We conclude from the results above that a plasma-membrane H+symporter encoded byC. albicans STL1actively transports glycerol intoC. albicanscells.
Identification of the binding site of the σ 54 hetero-oligomeric FleQ/FleT activator in the flagellar promoters of Rhodobacter sphaeroides
Authors: Peña-Sánchez J. , Poggio S. , Flores-Pérez U. , Osorio A. , Domenzain C. , Dreyfus G. , Camarena L.
Published: April 2009

Expression of the flagellar genes inRhodobacter sphaeroidesis dependent on one of the four sigma-54 factors present in this bacterium and on the enhancer binding proteins (EBPs) FleQ and FleT. These proteins, in contrast to other well-characterized EBPs, carry out activation as a hetero-oligomeric complex. To further characterize the molecular properties of this complex we mapped the binding sites or upstream activation sequences (UASs) of six different flagellar promoters. In most cases the UASs were identified at approximately 100 bp upstream from the promoter. However, the activity of the divergent promotersflhAp-flgAp, which are separated by only 53 bp, is mainly dependent on a UAS located approximately 200 bp downstream from each promoter. Interestingly, a significant amount of activation mediated by the upstream or contralateral UAS was also detected, suggesting that the architecture of this region is important for the correct regulation of these promoters. Sequence analysis of the regions carrying the potential FleQ/FleT binding sites revealed a conserved motif.In vivofootprinting experiments with themotAppromoter allowed us to identify a protected region that overlaps with this motif. These results allow us to propose a consensus sequence that represents the binding site of the FleQ/FleT activating complex.
Identification of resistance and virulence factors in an epidemic Enterobacter hormaechei outbreak strain
Authors: Paauw Armand , Caspers Martien P. M. , Leverstein-van Hall Maurine A. , Schuren Frank H. J. , Montijn Roy C. , Verhoef Jan , Fluit Ad C.
Published: April 2009

Bacterial strains differ in their ability to cause hospital outbreaks. Using comparative genomic hybridization, Enterobacter cloacae complex isolates were studied to identify genetic markers specific for Enterobacter cloacae complex outbreak strains. No outbreak-specific genes were found that were common in all investigated outbreak strains. Therefore, the aim of our study was to identify specific genetic markers for an Enterobacter hormaechei outbreak strain (EHOS) that caused a nationwide outbreak in The Netherlands. Most EHOS isolates carried a large conjugative plasmid (pQC) containing genes encoding heavy-metal resistance, mobile elements, pili-associated proteins and exported proteins as well as multiple-resistance genes. Furthermore, the chromosomally encoded high-pathogenicity island (HPI) was highly associated with the EHOS strain. In addition, other DNA fragments were identified that were associated with virulence: three DNA fragments known to be located on a virulence plasmid (pLVPK), as well as phage- and plasmid-related sequences. Also, four DNA fragments encoding putative pili with the most homology to pili of Salmonella enterica were associated with the EHOS. Finally, four DNA fragments encoding putative outer-membrane proteins were negatively associated with the EHOS. In conclusion, resistance and putative virulence genes were identified in the EHOS that may have contributed to increased epidemicity. The high number of genes detected in the EHOS that were related to transferable elements reflects the genomic plasticity of the E. cloacae complex and may explain the emergence of the EHOS in the hospital environment.
Molecular cloning and functional characterization of two CYP619 cytochrome P450s involved in biosynthesis of patulin in Aspergillus clavatus
Authors: Artigot Marie Pierre , Loiseau Nicolas , Laffitte Joelle , Mas-Reguieg Lina , Tadrist Souria , Oswald Isabelle P. , Puel Olivier
Published: April 2009

Patulin is an acetate-derived tetraketide mycotoxin produced by several fungal species, especially Aspergillus, Penicillium and Byssochlamys species. The health risks due to patulin consumption by humans have led many countries to regulate it in human food. Previous studies have shown the involvement of cytochrome P450 monooxygenases in the hydroxylation of two precursors of patulin, m-cresol and m-hydroxybenzylalcohol. In the present study, two cytochrome P450 genes were identified in the genome sequence of Aspergillus clavatus, a patulin-producing species. Both mRNAs were strongly co-expressed during patulin production. CYP619C2, encoded by the first gene, consists of 529 aa, while the second cytochrome, CYP619C3, consists of 524 aa. The coding sequences were used to perform the heterologous expression of functional enzymes in Saccharomyces cerevisiae. The bioconversion assays showed that CYP619C3 catalysed the hydroxylation of m-cresol to yield m-hydroxybenzyl alcohol. CYP619C2 catalysed the hydroxylation of m-hydroxybenzyl alcohol and m-cresol to gentisyl alcohol and 2,5-dihydroxytoluene (toluquinol), respectively. Except for the last compound, all enzyme products are known precursors of patulin. Taken together, these data strongly suggest the involvement of CYP619C2 and CYP619C3 in the biosynthesis of patulin. CYP619C2 and CYP619C3 are located near to two other genes involved in patulin biosynthesis, namely the 6-methylsalicylic acid synthase (6msas) and isoepoxydon dehydrogenase (idh) genes. The current data associated with an analysis of the sequence of A. clavatus suggest the presence of a cluster of 15 genes involved in patulin biosynthesis.
Impairment of d-alanine biosynthesis in Mycobacterium smegmatis determines decreased intracellular survival in human macrophages
Authors: Chacon Ofelia , Bermudez Luiz E. , Zinniel Denise K. , Chahal Harpreet K. , Fenton Robert J. , Feng Zhengyu , Hanford Kathy , Adams L. Garry , Barletta Raúl G.
Published: April 2009

d-Alanine is a structural component of mycobacterial peptidoglycan. The primary route ofd-alanine biosynthesis in eubacteria is the enantiomeric conversion froml-alanine, a reaction catalysed byd-alanine racemase (Alr).Mycobacterium smegmatis alrinsertion mutants are not dependent ond-alanine for growth and display a metabolic pattern consistent with an alternative pathway ford-alanine biosynthesis. In this study, we demonstrate that theM. smegmatis alrinsertion mutant TAM23 can synthesized-alanine at lower levels than the parental strain. The insertional inactivation of thealrgene also decreases the intracellular survival of mutant strains within primary human monocyte-derived macrophages. By complementation studies, we confirmed that the impairment ofalrgene function is responsible for this reduced survival. Inhibition of superoxide anion and nitric oxide formation in macrophages suppresses the differential survival. In contrast, for bacteria grown in broth, both strains had approximately the same susceptibility to hydrogen peroxide, acidified sodium nitrite, low pH and polymyxin B. In contrast, TAM23 exhibited increased resistance to lysozyme.d-Alanine supplementation considerably increased TAM23 viability in nutritionally deficient media and within macrophages. These results suggest that nutrient deprivation in phagocytic cells combined with killing mediated by reactive intermediates underlies the decreased survival ofalrmutants. This knowledge may be valuable in the construction of mycobacterial auxotrophic vaccine candidates.
Characterization of a novel air–liquid interface biofilm of Pseudomonas fluorescens SBW25
Authors: Koza Anna , Hallett Paul D. , Moon Christina D. , Spiers Andrew J.
Published: April 2009

Pseudomonads are able to form a variety of biofilms that colonize the air–liquid (A–L) interface of static liquid microcosms, and differ in matrix composition, strength, resilience and degrees of attachment to the microcosm walls. FromPseudomonas fluorescensSBW25, mutants have evolved during prolonged adaptation–evolution experiments which produce robust biofilms of the physically cohesive class at the A–L interface, and which have been well characterized. In this study we describe a novel A–L interface biofilm produced by SBW25 that is categorized as a viscous mass (VM)-class biofilm. Several metals were found to induce this biofilm in static King's B microcosms, including copper, iron, lead and manganese, and we have used iron to allow further examination of this structure. Iron was demonstrated to induce SBW25 to express cellulose, which provided the matrix of the biofilm, a weak structure that was readily destroyed by physical disturbance. This was confirmedin situby a low (0.023–0.047 g) maximum deformation mass and relatively poor attachment as measured by crystal violet staining. Biofilm strength increased with increasing iron concentration, in contrast to attachment levels, which decreased with increasing iron. Furthermore, iron added to mature biofilms significantly increased strength, suggesting that iron also promotes interactions between cellulose fibres that increase matrix interconnectivity. Whilst weak attachment is important in maintaining the biofilm at the A–L interface, surface-interaction effects involving cellulose, which reduced surface tension by ∼3.8 mN m−1, may also contribute towards this localization. The fragility and viscoelastic nature of the biofilm were confirmed by controlled-stress amplitude sweep tests to characterize critical rheological parameters, which included a shear modulus of 0.75 Pa, a zero shear viscosity of 0.24 Pa s−1and a flow point of 0.028 Pa. Growth and morphological data thus far support a non-specific metal-associated physiological, rather than mutational, origin for production of the SBW25 VM biofilm, which is an example of the versatility of bacteria to inhabit optimal niches within their environment.
Strain-specific impact of PsaR of Streptococcus pneumoniae on global gene expression and virulence
Authors: Hendriksen Wouter T. , Bootsma Hester J. , van Diepen Angela , Estevão Silvia , Kuipers Oscar P. , de Groot Ronald , Hermans Peter W. M.
Published: April 2009

Previous studies have indicated that PsaR of Streptococcus pneumoniae is a manganese-dependent regulator, negatively affecting the expression of at least seven genes. Here, we extended these observations by transcriptome and proteome analysis of psaR mutants in strains D39 and TIGR4. The microarray analysis identified three shared PsaR targets: the psa operon, pcpA and prtA. In addition, we found 31 genes to be regulated by PsaR in D39 only, most strikingly a cellobiose-specific phosphotransferase system (PTS) and a putative bacteriocin operon (sp0142–sp0146). In TIGR4, 14 PsaR gene targets were detected, with the rlrA pathogenicity islet being the most pronounced. Proteomics confirmed most of the shared gene targets. To examine the contribution of PsaR to pneumococcal virulence, we compared D39 and TIGR4 wild-type (wt) and psaR mutants in three murine infection models. During colonization, no clear effect was observed of the psaR mutation in either D39 or TIGR4. In the pneumonia model, small but significant differences were observed in the lungs of mice infected with either D39wt or ΔpsaR: D39ΔpsaR had an initial advantage in survival in the lungs. Conversely, TIGR4ΔpsaR-infected mice had significantly lower bacterial loads at 24 h only. Finally, during experimental bacteraemia, D39ΔpsaR-infected mice had significantly lower bacterial loads in the bloodstream than wt-infected mice for the first 24 h of infection. TIGR4ΔpsaR showed attenuation at 36 h only. In conclusion, our results show that PsaR of D39 and TIGR4 has a strain-specific role in global gene expression and in the development of bacteraemia in mice.
Investigation of the role of the BAM complex and SurA chaperone in outer-membrane protein biogenesis and type III secretion system expression in Salmonella
Authors: Fardini Yann , Trotereau Jérôme , Bottreau Elisabeth , Souchard Charlène , Velge Philippe , Virlogeux-Payant Isabelle
Published: April 2009

In Escherichia coli, the assembly of outer-membrane proteins (OMP) requires the BAM complex and periplasmic chaperones, such as SurA or DegP. Previous work has suggested a potential link between OMP assembly and expression of the genes encoding type-III secretion systems. In order to test this hypothesis, we studied the role of the different lipoproteins of the BAM complex (i.e. BamB, BamC, BamD and BamE), and the periplasmic chaperones SurA and DegP, in these two phenotypes in Salmonella. Analysis of the corresponding deletion mutants showed that, as previously described with the ΔbamB mutant, BamD, SurA and, to a lesser extent, BamE play a role in outer-membrane biogenesis in Salmonella Enteritidis, while the membrane was not notably disturbed in ΔbamC and ΔdegP mutants. Interestingly, we found that BamD is not essential in Salmonella, unlike its homologues in Escherichia coli and Neisseria gonorrhoeae. In contrast, BamD was the only protein required for full expression of T3SS-1 and flagella, as demonstrated by transcriptional analysis of the genes involved in the biosynthesis of these T3SSs. In line with this finding, bamD mutants showed a reduced secretion of effector proteins by these T3SSs, and a reduced ability to invade HT-29 cells. As ΔsurA and ΔbamE mutants had lower levels of OMPs in their outer membrane, but showed no alteration in T3SS-1 and flagella expression, these results demonstrate the absence of a systematic link between an OMP assembly defect and the downregulation of T3SSs in Salmonella; therefore, this link appears to be related to a more specific mechanism that involves at least BamB and BamD.
Identification of surface proteins involved in the adhesion of a probiotic Bacillus cereus strain to mucin and fibronectin
Authors: Sánchez B. , Arias S. , Chaignepain S. , Denayrolles M. , Schmitter J. M. , Bressollier P. , Urdaci M. C.
Published: April 2009

SeveralBacillusstrains isolated from commercial probiotic preparations were identified at the species level, and their adhesion capabilities to three different model intestinal surfaces (mucin, Matrigel and Caco-2 cells) were assessed. In general, adhesion of spores was higher than that of vegetative cells to the three matrices, and overall strainBacillus cereusCHdisplayed the best adhesion. Different biochemical treatments revealed that surface proteins ofB. cereusCHwere involved in the adhesion properties of the strain. Surface-associated proteins from vegetative cells and spores ofB. cereusCHwere extracted and identified, and some proteins such as S-layer components, flagellin and cell-bound proteases were found to bind to mucin or fibronectin. These facts suggest that those proteins might play important roles in the interaction of this probioticBacillusstrain within the human gastrointestinal tract.
Characterization of the pathogenicity island protein PdpA and its role in the virulence of Francisella novicida
Authors: Schmerk Crystal L. , Duplantis Barry N. , Wang Diana , Burke Robert D. , Chou Alicia Y. , Elkins Karen L. , Ludu Jagjit S. , Nano Francis E.
Published: April 2009

Francisella tularensisis a highly virulent, intracellular pathogen that causes the disease tularaemia. A research surrogate forF. tularensisisFrancisella novicida, which causes a tularaemia-like disease in mice, grows similarly in macrophages, and yet is unable to cause disease in humans. BothFrancisellaspecies contain a cluster of genes referred to as theFrancisellapathogenicity island (FPI). Pathogenicity determinant protein A (PdpA), encoded by thepdpAgene, is located within the FPI and has been associated with the virulence ofFrancisellaspecies. In this work we examined the properties of PdpA protein expression and localization as well as the phenotype of aF. novicida pdpAdeletion mutant. Monoclonal antibody detection of PdpA showed that it is a soluble protein that is upregulated in iron-limiting conditions and undetectable in anmglAormglBmutant background. Deletion ofpdpAresulted in a strain that was highly attenuated for virulence in chicken embryos and mice.
Simultaneous lack of catalase and beta-toxin in Staphylococcus aureus leads to increased intracellular survival in macrophages and epithelial cells and to attenuated virulence in murine and ovine models
Authors: Martínez-Pulgarín Susana , Domínguez-Bernal Gustavo , Orden José A. , de la Fuente Ricardo
Published: April 2009

Staphylococcus aureus produces a variety of virulence factors that allow it to cause a wide range of infections in humans and animals. In the latter, S. aureus is a leading cause of intramammary infections. The contribution of catalase (KatA), an enzyme implicated in oxidative stress resistance, and beta-toxin (Hlb), a haemolysin, to the pathogenesis of S. aureus is poorly characterized. To investigate the role of these enzymes as potential virulence factors in S. aureus, we examined the intracellular survival of ΔkatA, Δhlb and ΔkatA Δhlb mutants in murine macrophages (J774A.1) and bovine mammary epithelial cells (MAC-T), and their virulence in different murine and ovine models. Catalase was not required for the survival of S. aureus within either J774A.1 or MAC-T cells. However, it was necessary for the intracellular proliferation of the bacterium after invasion of MAC-T cells. In addition, catalase was not needed for the full virulence of S. aureus in mice. Deletion of the hlb gene had no effect on the intracellular survival of S. aureus in J774A.1 cells but did cause a slight increase in survival in MAC-T cells. Furthermore, like catalase, beta-toxin was not required for complete virulence of S. aureus in murine models. Unexpectedly, the ΔkatA Δhlb mutant showed a notably increased persistence in both cell lines, and was significantly less virulent for mice than were the wild-type strain and single mutants. Most interestingly, it was also markedly attenuated in intramammary and subcutaneous infections in ewes and lambs.
Protective capacities of cell surface-associated proteins of Streptococcus suis mutants deficient in divalent cation-uptake regulators
Authors: Aranda Jesús , Garrido Maria Elena , Fittipaldi Nahuel , Cortés Pilar , Llagostera Montserrat , Gottschalk Marcelo , Barbé Jordi
Published: April 2009

Many cell surface-associated, divalent cation-regulated proteins are immunogenic, and some of them confer protection against the bacterial species from which they are derived. In this work, twoStreptococcus suisdivalent cation uptake regulator genes controlling zinc/manganese and iron uptake (adcRandfur, respectively) were inactivated in order to study the protective capacities of their cell surface-associated proteins. The results obtained showed overexpression of a set of immunogenic proteins (including members of the pneumococcal histidine triad family previously reported to confer protection against streptococcal pathogens) inS. suis adcRmutant cell surface extracts. Likewise, genes encoding zinc transporters, putative virulence factors and a ribosomal protein paralogue related to zinc starvation appeared to be derepressed in this mutant strain. Moreover, protection assays in mice showed that although neitheradcR- norfur-regulated cell surface-associated proteins were sufficient to confer protection in mice, the combination of bothadcR- andfur-regulated cell surface-associated proteins is able to confer significant protection (50 %,P=0.038) against a challenge to mice vaccinated with them.
Gis1 is required for transcriptional reprogramming of carbon metabolism and the stress response during transition into stationary phase in yeast
Authors: Zhang Nianshu , Wu Jian , Oliver Stephen G.
Published: April 2009

Transition from growth to the stationary phase in yeast is still poorly understood. Previously, we identified a group of yeast genes that are universally upregulated upon starvation for different macronutrients. Here, we demonstrate that the Gis1 transcription factor and the Rim15 kinase are responsible for the upregulation of many of these genes. In chemostat cultures, gis1 or rim15 mutant cells are outcompeted by their wild-type parents under conditions resembling the later stages of diauxie (glucose-limiting) and post-diauxie (ethanol as a carbon source). Whilst Gis1p and Rim15p have distinct functions in gene repression, the growth defects of gis1 or rim15 deletants can be accounted for by the overlapping functions of their protein products in promoting the expression of genes involved in glutamate biosynthesis, the glyoxylate cycle, the pentose phosphate pathway and the stress response. Further, we show that the sets of GIS1- and RIM15-dependent genes and the degree of their regulation change in response to the identity of the carbon source, suggesting the likely dynamics of gene regulation exerted by Rim15p and Gis1p during different phases of the transition into stationary phase. In particular, Rim15p is required for the expression of genes involved in gluconeogenesis/glycolysis and glycerol biosynthesis only when ethanol is used as the carbon source. In agreement with this, Rim15p is shown to act in parallel with Hog1p to defend cells against osmotic stress.
Cellular chain formation in Escherichia coli biofilms
Authors: Vejborg Rebecca Munk , Klemm Per
Published: April 2009

In this study we report on a novel structural phenotype in Escherichia coli biofilms: cellular chain formation. Biofilm chaining in E. coli K-12 was found to occur primarily by clonal expansion, but was not due to filamentous growth. Rather, chain formation was the result of intercellular interactions facilitated by antigen 43 (Ag43), a self-associating autotransporter (SAAT) protein, which has previously been implicated in auto-aggregation and biofilm formation. Immunofluorescence microscopy suggested that Ag43 was concentrated at or near the cell poles, although when the antigen was highly overexpressed, a much more uniform distribution was seen. Immunofluorescence microscopy also indicated that other parameters, including dimensional constraints (flow, growth alongside a surface), may also affect the final biofilm architecture. Moreover, chain formation was affected by other surface structures; type I fimbriae expression significantly reduced cellular chain formation, presumably by steric hindrance. Cellular chain formation did not appear to be specific to E. coli K-12. Although many urinary tract infection (UTI) isolates were found to form rather homogeneous, flat biofilms, three isolates, including the prototypic asymptomatic bacteriuria strain, 83972, formed highly elaborate cellular chains during biofilm growth in human urine. Combined, these results illustrate the diversity of biofilm architectures that can be observed even within a single microbial species.
The high-affinity phosphate transporter Pst in Proteus mirabilis HI4320 and its importance in biofilm formation
Authors: O'May G. A. , Jacobsen S. M. , Longwell M. , Stoodley P. , Mobley H. L. T. , Shirtliff M. E.
Published: April 2009

Proteus mirabiliscauses urinary tract infections (UTIs) in individuals requiring long-term indwelling catheterization. The pathogenesis of this uropathogen is mediated by a number of virulence factors and the formation of crystalline biofilms. In addition, micro-organisms have evolved complex systems for the acquisition of nutrients, including the phosphate-specific transport system, which has been shown to be important in biofilm formation and pathogenesis. A functional Pst system is important during UTIs caused byP. mirabilisHI4320, since transposon mutants in the PstS periplasmic binding protein and the PstA permease protein were attenuated in the CBA mouse model of UTI. These mutants displayed a defect in biofilm formation when grown in human urine. This study focuses on a comparison of the proteomes during biofilm and planktonic growth in phosphate-rich medium and human urine, and microscopic investigations of biofilms formed by thepstmutants. Our data suggest that (i) the Δpstmutants, and particularly the ΔpstSmutant, are defective in biofilm formation, and (ii) the proteomes of these mutants differ significantly from that of the wild-type. Therefore, since the Pst system ofP. mirabilisHI4320 negatively regulates biofilm formation, this system is important for the pathogenesis of these organisms during complicated UTIs.
Evolution of colicin BM plasmids: the loss of the colicin B activity gene
Authors: Christenson Julia K. , Gordon David M.
Published: April 2009

Colicins, a class of antimicrobial compounds produced by bacteria, are thought to be important mediators of intra- and interspecific interactions, and are a significant factor in maintaining microbial diversity. Colicins B and M are among the most common colicins produced byEscherichia coli, and are usually encoded adjacently on the same plasmid. In this study, the characterization of a collection ofE. coliisolated from Australian vertebrates revealed that a significant fraction of colicin BM strains lack an intact colicin B activity gene. The colicin B and M gene region was sequenced in 60 strains and it was found (with one exception) that all plasmids lacking an intact colicin B activity gene have an identical colicin gene structure, possessing a complete colicin B immunity gene and a 130 bp remnant of the B activity gene. A phylogenetic analysis of the colicin M and B operons and characterization of the plasmids suggested that ColBM plasmids with a truncated B activity gene have evolved on at least three separate occasions. Colicin B immunity was found to be non-functional in strains that have lost colicin B activity, and colicin M was still produced despite the absence of the SOS box believed to regulate its production in colicin BM strains. The presence of a remnant of the microcin V operon next to the truncated colicin B activity gene indicated that these plasmids evolved as a consequence of gene transfer between colicin BM and microcin V plasmids. We suggest that these transfer events most likely involved the transfer of some microcin V genes and associated virulence factors onto ColBM plasmids.
Galleria mellonella as an alternative infection model for Yersinia pseudotuberculosis
Authors: Champion Olivia L. , Cooper Ian A. M. , James Sarah L. , Ford Donna , Karlyshev Andrey , Wren Brendan W. , Duffield Melanie , Oyston Petra C. F. , Titball Richard W.
Published: April 2009

We report that larvae of the wax moth (Galleria mellonella) are susceptible to infection with the human enteropathogenYersinia pseudotuberculosisat 37 °C. Confocal microscopy demonstrated that in the initial stages of infection the bacteria were taken up into haemocytes. To evaluate the utility of this model for screeningY. pseudotuberculosismutants we constructed and tested a superoxide dismutase C (sodC) mutant. This mutant showed increased susceptibility to superoxide, a key mechanism of killing in insect haemocytes and mammalian phagocytes. It showed reduced virulence in the murine yersiniosis infection model and in contrast to the wild-type strain IP32953 was unable to killG. mellonella. The complemented mutant regained all phenotypic properties associated with SodC, confirming the important role of this metalloenzyme in twoY. pseudotuberculosisinfection models.
LuxR-family ‘solos’: bachelor sensors/regulators of signalling molecules
Authors: Subramoni Sujatha , Venturi Vittorio
Published: April 2009

N-Acylhomoserine lactone (AHL) quorum-sensing (QS) signalling is the best-understood chemical language in proteobacteria. In the last 15 years a large amount of research in several bacterial species has revealed in detail the genetic, molecular and biochemical mechanisms underlying AHL signalling. These studies have revealed the role played by protein pairs of the AHL synthase belonging to the LuxI family and cognate LuxR-family AHL sensor–regulator. Proteobacteria however commonly possess a QS LuxR-family protein for which there is no obvious cognate LuxI synthase; these proteins are found in bacteria which possess a complete AHL QS system(s) as well as in bacteria that do not. Scientists are beginning to address the roles played by these proteins and it is emerging that they could allow bacteria to respond to endogenous and exogenous signals produced by their neighbours. AHL QS research thus far has mainly focused on a cell-density response involving laboratory monoculture studies. Recent findings on the role played by the unpaired LuxR-family proteins highlight the need to address bacterial behaviour and response to signals in mixed communities. Here we review recent progress with respect to these LuxR proteins, which we propose to call LuxR ‘solos’ since they act on their own without the need for a cognate signal generator. Initial investigations have revealed that LuxR solos have diverse roles in bacterial interspecies and interkingdom communication.