bluuebunny/crossref_metadata_2025 huggingface dataset:
Nodulation of Phaseolus vulgaris L. as affected by Rhizobium phaseoli growth phase
Authors: Boiardi J. L. , Galar M. L.
Published: May 2010

The influence of culture age and of growth rate on the nodulation ability of strain F 45 str. Rhizobium phaseoli was studied. Roots of Phaseolus vulgaris L., grown in pouches, were infected with rhizobial suspensions (about 1 × 105 cells/root) taken from different batch cultures at different growth phases. After 24 h the free bacterial population was inhibited by adding tetracycline to the rooting medium. Nodules were counted 15–20 days after inoculation. More nodulation was obtained with rhizobia from early, mid, or late exponential phase than from lag or stationary phases. Differences in nodulation obtained had no correlation to the root attachment capacity of the cells nor to the rhizobial binding to Phaseolus vulgaris L. seed lectin. Bacterial attachment to bean roots was maximal with stationary phase bacteria, while lectin binding reached its maximal value with early exponential phase rhizobia, being very low with mid exponential phase cells. These results suggested that the difference in nodulation achieved with Rhizobium phaseoli at different growth phases could be caused by a step of the infection process not related to early (1 h) microbial attachment to roots nor to bacterial binding to Phaseolus vulgaris L. lectin.
Distinction of cnxH cofactor gene-specified protomers with monoclonal antibodies to Aspergillus nitrate reductase
Authors: Downey R. J. , South P. A.
Published: May 2010

The nitrate reductase (NADPH) (EC 1.6.6.3) from Aspergillus nidulans is influenced directly by mutations in the structural gene (niaD) for the major subunit of the enzyme and indirectly by mutation in any of several molybdenum cofactor loci (cnx). The cnxE-14 and the cnxH-3 mutants have been noted to contain the enzyme in two distinct forms following induction with nitrate. With the cnxH-3 as a prototype cnxH mutant, 10 other cnxH were found to be devoid of the assembled (dimeric) form of the enzyme. Two monoclonal antibodies specific for the native enzyme of the wild type (biA-1) recognized an epitope on the enzyme from the cnxE-14 and cnxH-3 mutants that was common to both and another that was unique to the cnxH gene specified protomer. Another monoclonal antibody recognized an epitope that occurs only in the assembled dimeric form of the enzyme from the wild type or the cnxE-14 mutant. The experiments further substantiate the cnxH phenotype as one involving unassembled protomers of the nitrate reductase in Aspergillus.
Nutritional requirements for growth of Methanothrix concilii
Authors: Patel G. B. , Baudet C. , Agnew B. J.
Published: May 2010

Methanothrix concilii, which is a mesophilic, aceticlastic methanogen, required 6.8 mM inorganic nitrogen for maximal growth rate in a mineral salts – vitamins medium containing 73.5 mM acetic acid. Cysteine hydrochloride, sodium sulfide, or glutathione at optimum concentrations of 6.0, 1.0, and 12.0 mM, respectively, served as the sole source of sulphur for growth. Of the 10 vitamins tested, only biotin, thiamine hydrochloride, and p-aminobenzoic acid stimulated growth. The optimum iron and nickel concentrations were 1–5 and 0.1 μM, respectively. Both calcium and magnesium, at an optimum concentration of 250 and 500 μM, respectively, were essential for growth. The optimum concentrations of manganese, cobalt, and zinc, in conjunction with one another, were 2.5, 10.0, and 5.0 μM, respectively.
The presence of Listeria spp. in raw milk in Ontario
Authors: Farber Jeffrey M. , Sanders Gregory W. , Malcolm Stephen A.
Published: May 2010

Raw milk samples from bulk tanks in Ontario were analyzed for the presence of Listeria species. The overall incidence of Listeria species in raw milk was 12.4%. Listeria innocua was most frequently isolated and was found in 9.7% (43/445) of the raw milk samples, while L. monocytogenes and L. welshimeri were each found in 1.3% (6/455) of the samples. No other species of Listeria was found. Of five regions in Ontario that were examined, the eastern region had a significantly higher incidence rate of Listeria species than the western, northern, or northwestern regions. There was also a significantly lower incidence rate of Listeria species in winter than in the other three seasons. A comparison of several cold enrichment and shortened enrichment procedures demonstrated that no single procedure was totally satisfactory in isolating Listeria species.
Isolation and partial characterization of a bacteriophage active on Hyphomicrobium sp. WI-926
Authors: Preissner W. C. , Maier S. , Völker H. , Hirsch P.
Published: May 2010

Isolation of a Hyphomicrobium phage from raw sewage from Athens, Ohio, was achieved by a combination of differential centrifugation, filtration, enrichment in mixed Hyphomicrobium cultures, and purification on individual host strains by subculturing single plaques in soft agar overlayers. Enrichments with water from Lake Erie and Lake Beechwood (Ohio) were unsuccessful. Out of 21 Hyphomicrobium strains and 22 other Gram-negative and Gram-positive bacteria tested, only Hyphomicrobium WI-926 (isolated from a German forest pond) was susceptible. This phage had an isometric head (diameter between opposite apices, 67 nm) and a short (12 nm), noncontractile tail and belongs thus to the morphogroup C1. It contained double-stranded DNA. The single-step growth curve showed a latent period of 9 h, a rise period of 6 h, and a burst size of 35. The various differentiation stages in the host development exhibited different affinities for phage adsorption and development. While all stages allowed phage adsorption, the daughter cells were most efficient. Phage multiplication was limited to daughter cells, and the development of infected swarmer cells was arrested permanently at this stage.
Induction of the xylitol dehydrogenase of Pullularia pullulans
Authors: Sugai Juliet K. , Veiga L. A.
Published: May 2010

Pullularia pullulans, a yeastlike fungus, metabolizes xylitol via an intracellular xylitol dehydrogenase. Formation of the enzyme was induced by D-xylose and inhibited by cycloheximide, suggesting de novo synthesis. The induction study was carried out with noninduced cells of P. pullulans harvested from a glycerol medium. The cells initiated synthesis of xylitol dehydrogenase without a detectable lag phase when 1.5% xylose was added. The differential rate of xylitol dehydrogenase synthesis was 1.4 units per mg of synthesized protein. Kinetic studies of enzyme induction in a growing culture showed that the highest level of specific activity was reached at 25 to 27 h of growth, with an increase of 200 times over the basal level in the glycerol medium.
Glucose effect on induction of the xylitol dehydrogenase of Pullularia pullulans
Authors: Sugai Juliet , Veiga L. A.
Published: May 2010

Pullularia pullulans grown on D-xylose is induced to synthesize xylitol dehydrogenase, which catalyses the oxidation of xylitol to D-xylulose. When glucose was added to a culture or to resting cells actively synthesizing xylitol dehydrogenase, inhibition of enzyme-induced synthesis was observed. This effect was transient (transient catabolic inhibition) and was followed by a weak permanent catabolite repression. Glucose continued to cause inhibition, even after cycloheximide was added. However, when enzyme induction reached its maximum, the presence of glucose was no longer inhibitory. A rapid and complete recovery of enzyme activity to the initial level occurred when glucose-inhibited cells were incubated without glucose. Exogenous adenosine 3′,5′-cyclic monophosphate reverses this "glucose effect."
The yeast aminopeptidase Y
Authors: Nowak J. , Tsai H.
Published: May 2010

A metal-dependent aminopeptidase (EC 3.4.11.-), designated APase Y, has been purified to homogeneity by conventional methods. The enzyme is composed of a single polypeptide chain with molecular mass of 102 kilodaltons, estimated by sodium dodecyl sulphate – polyacrylamide gel electrophoresis, with a blocked N-terminal amino acid. It possesses neither endopeptidase nor carboxypeptidase activity and is strongly inhibited by metal-chelating agents, Zn2+, and the protein inhibitor from Neurospora crassa. APase Y is insensitive to Cl anions, S—S reducing reagents, serine protease inhibitors, and the peptidase inhibitor benzamidine. Co2+, Hg2+, and p-chloromercuribenzoate can activate the enzyme up to 22, 20, and 55%, respectively. The holoenzyme is resistant to yeast endopeptidases A, B, and Y, whereas the apoenzyme (obtained after treatment with chelators) is susceptible to the serine endopeptidases B and Y. The enzyme catalyzes hydrolysis of most L peptides possessing free α-amino (or imino) group by stepwise removal of N-terminal residue. Peptides with L-leucine at the N terminus are cleaved preferentially. The enzyme is unable to catalyze hydrolysis of X—Pro type peptide bonds, and inefficiently hydrolyzes bonds between Asp—X and Glu—X. L-leucine p-nitroanilide hydrolyzes optimally at pH 8.2 with a Km value of 1 mM. The purified enzyme is stable during storage in 0.05 M phosphate buffer, pH 6.7, containing 40–50% glycerol, at −20 °C.
Characterization of Chlamydia trachomatis antigens with monoclonal and polyclonal antibodies
Authors: Maclean Ian W. , Peeling Rosanna W. , Brunham Robert C.
Published: May 2010

We used monoclonal antibodies (MAbs) to examine the antigenic specificity and biologic function of several Chlamydia trachomatis antigens. Thirteen distinct MAbs to eight C. trachomatis antigens were produced. Six MAbs reacted with unique epitopes on the major outer membrane protein (MOMP) and two of these had neutralizing activity. MAbs were produced to each of the chlamydial antigens with molecular masses of 10, 29, 32, 57, 60, 70, and 75 kilodaltons (kDa). These MAbs showed species and genus specificity in an immunoblot assay. None of the MAbs had neutralizing activity. The epitopes recognized on MOMP, 29-, and 10-kDa (presumably lipopolysaccharide) antigens were surface exposed. MAbs to the 75-kDa, 57-kDa, and MOMP antigens were used for immunoaffinity purification of these antigens to produce monospecific antisera in mice. With polyclonal sera, we found that the 75-kDa antigen was also immunoaccessible and that antibody to MOMP and 75-kDa antigens neutralized C. trachomatis infectivity. We conclude that, in addition to MOMP and lipopolysaccharide, antigens with molecular masses of 75 and 29 kDa are surface exposed. Antibodies to MOMP and 75-kDa antigens can neutralize the organism in vitro.
Ethanol and carbon-source starvation enhance the accumulation of HSP80 in Neurospora crassa
Authors: Roychowdhury H. S. , Kapoor M.
Published: May 2010

In Neurospora crassa, heat shock results in the induction of 9 to 11 heat shock proteins (HSP), of which HSP80 is the most abundant and the first to be synthesized. The induction of HSP80 was investigated during normal growth (2% sucrose) and under sucrose starvation. Transfer of mycelium to a medium supplemented with ethanol stimulated the synthesis of HSP80, even at the normal growth temperature of 28 °C. It was also synthesized under carbon starvation conditions, where the medium was supplemented with 0.02% sucrose, 0.3% acetate, 0.2% lactate, or ethanol. A 30–35 kilodalton polypeptide was induced by heat shock in carbon-sufficient media, but in 0.02% sucrose and 0.3% acetate containing media it was synthesized at normal temperatures. While the overall heat shock response remained unaltered in these cultures, the abundance of HSP90 and HSP70, relative to HSP80, was greater. HSP80 appears to be controlled by carbon-catabolite repression as well as heat shock. Another high molecular mass protein (tentatively designated alc'80') was observed to be induced by heat shock, provided carbon starvation conditions prevailed concurrently.
Effects of ionophore A23187 on ciliary activity of Paramecium caudatum
Authors: Doughty Michael J.
Published: May 2010

The ciliated protozoan Paramecium caudatum (suspended in buffered solutions of pH 4.5–9.5) was treated with the ionophore A23187. With calcium and sodium as the only added extracellular cations, A23187 stopped ciliary motion and immobilized the cells. The rate of immobilization increased as a function of A23187 concentration (0.5–16 μg/mL) and extracellular calcium concentration (0.016–4 mM), but decreased as a function of increasing extracellular pH. The rate of immobilization was markedly sensitive to the extracellular calcium ion concentration at alkaline pH, but showed only slight calcium sensitivity at acid pH values. Continuous ciliary reversal (and thus backward swimming motion of the cells) was not observed under these conditions. However, extracellular magnesium ions (in a concentration-dependent manner) attenuated and even prevented the immobilization induced by calcium–A23187 treatment. In addition, in the presence of 1 mM Mg2+, a periodic ciliary reversal response was induced by calcium–A23187 treatment. At neutral pH values, the duration of this response increased as a function of extracellular calcium, but not magnesium, ion concentration. At neutral to alkaline pH values, a sustained slow backward swimming or circling motion (partial ciliary reversal) occurred after the period of periodic ciliary reversal.
Interaction of Candida albicans with genital mucosa: effect of sex hormones on adherence of yeasts in vitro
Authors: Kalo Aliza , Segal Esther
Published: May 2010

Findings from our previous studies revealed a correlation between the level of adherence in vitro of Candida albicans to human exfoliated vaginal epithelial cells (VEC) and the hormonal status of the cell donors. In the present study we investigated the effect of the sex hormones estradiol, estriol, progesterone, and testosterone on the binding of the yeasts to HeLa cell lines and VEC in vitro. Monolayers of HeLa cells were exposed to the hormones and yeasts under controlled conditions. The number of adherent yeasts per square millimetre of HeLa cell monolayers and the percentage of VEC with adherent yeasts was estimated by microscopic counts. The results showed that the tested sex hormones affected at various degrees the adhesion of yeasts to HeLa cells or VEC. Progesterone had the most marked effect, leading to a significant increase in the number of adherent yeasts to HeLa cells or in the percentage of adhesion of VEC. In addition, VEC were separated on Percoll gradients into the two cell types: superficial (S) and intermediate (I), cell types which appear physiologically under increased serum levels of estradiol or progesterone, respectively. Adhesion assays with the separated cell populations revealed an increased binding capacity of the I cells. The finding that progesterone increased the adherence of yeasts to genital mucosa and that VEC of the I type have a higher capacity to adhere the yeasts is compatible with our previous observation that increased numbers of I cells, appearing under high level of progesterone, are found in situations known to have predisposition to vaginal candidiasis. Thus, our data point to a possible involvement of the hormone progesterone in the adherence of C. albicans to genital epithelium.
Implications of rhizosphere competence of Trichoderma harzianum
Authors: Ahmad Jaleed S. , Baker Ralph
Published: May 2010

Seed treatment with conidia of rhizosphere-competent mutants of Trichoderma harzianum reduced the incidence of preemergence damping-off of barley, cucumber, pea, radish, and tomato induced by Pythium ultimum. Wild-type parents of these mutants were less effective in control. When rhizosphere-competent mutants were applied to seed or when a peat-bran preparation was added to soil, the resulting plants produced significantly higher fruit weight and higher dry weights than those treated with rhizosphere-incompetent wild types and controls. Seed treatment with mutants increased the incidence of emergence and resultant plant growth was significantly (P = 0.05) better than when mutant strains were added to soil in peat–bran. There was, however, no significant (P = 0.05) difference between the two types of application of the wild types. When cucumber seeds, treated with a T. harzianum rhizosphere-competent mutant (T-95) or its parent wild type (WT), were sown in raw soil kept under constant matric potential with no additional water added, the roots grew 8 cm in 8 days. Untreated seeds produced roots 7 cm long. Fewer colony-forming units of P. ultimum per milligram were isolated from rhizosphere soil of the T-95 treated seedlings than in the untreated controls and those treated with WT. Pythium ultimum was not detected in the 8th cm (farthest from seed) root segment of T-95 treated seeds, whereas the last centimetre of root segment from untreated and WT-treated seeds yielded 3000 colony-forming units/g rhizosphere soil. Seed treatment with rhizosphere-competent mutants of T. harzianum is an effective delivery system to achieve biocontrol and increase growth response.
A comparative study of virulent and avirulent strains of Chromobacterium violaceum
Authors: Miller Donna P. , Blevins W. T. , Steele D. B. , Stowers M. D.
Published: May 2010

A clinical isolate and a soil isolate of Chromobacterium violaceum were compared to determine differences in virulence-related characteristics. Purified lipopolysaccharide (endotoxin) from the virulent, clinical strain was more reactive than that from the avirulent soil strain as determined by the Limulus amebocyte lysate assay. There were no differences in hemolysin or cyanide production between the two strains. The virulent strain was more resistant to phagocytosis and intracellular killing by human polymorphonucleocytes. The clinical strain showed a superoxide dismutase activity 30% higher and a catalase activity fivefold higher than the activities of the soil-isolated strain. The clinical strain also was capable of producing approximately twice as much hydrogen peroxide during growth as compared with the soil isolate. This study suggests that virulence of C. violaceum may be, at least in part, associated with endotoxin, and some protection of the virulent, clinical strain from phagocytic attack is afforded by elevated levels of superoxide dismutase and catalase.
Statistical considerations associated with the use of the heterotrophic activity method for estimating Vmax and K′ for aquatic environments
Authors: Choquet C. G. , Ferroni G. D. , Leduc L. G. , Robinson Joseph A.
Published: May 2010

This article deals with whether linear or nonlinear, ordinary least-squares regression analysis is superior in the estimation of the kinetic parameters Vmax and K′ from data sets generated by the Wright–Hobbie heterotrophic activity method. An analysis of variance showed that weighting of data was theoretically required for the optimal estimation of Vmax and K′ for both models. However, the magnitude of the parameter estimates was largely independent of the weighting function employed. Monte-Carlo analysis also indicated that the nature of the weighting function did not appreciably affect the parameter estimates, and more importantly, that there was not a strong statistical justification for the use of the nonlinear model over the linear model in the estimation of Vmax and K′.
An overview of some mechanisms of bacterial pathogenesis
Authors: Conway Brian , Ronald Allan
Published: May 2010

The adherence of microorganisms to host surfaces is highly specific, and in many cases, essential for subsequent pathogenetic events to occur. A dynamic process leading to increased mucosal adherence of gram-negative bacilli to epithelial cell receptors in the oral cavity appears to be the initial step in the development of pneumonia. In infectious processes secondary to Streptococcus pneumoniae, adherence may also play a role in specific syndromes. In many cases, however, colonization of oropharyngeal mucus itself, the presence of capsular polysaccharide, and the release of various cell wall components appear to interact to cause clinical disease. In Neisseria gonorrhoeae infections, adherence is all important and is mediated by a number of cell surface structures. These have been studied extensively. Many of these structures, such as pili and protein II, exhibit great variability both between strains and in the same organism at different stages of infection. Others, such as protein I, are more constant. This information has been used in the production of specific vaccines to more preserved structures to inhibit adherence. These will be tested in the near future. It is our view that a better understanding of the many forms of bacterial adherence will be the key to our designing more effective strategies to detect early infection and to intervene more decisively to limit its spread.
The role of bacterial hydrophobicity in infection: bacterial adhesion and phagocytic ingestion
Authors: Absolom Darryl R.
Published: May 2010

The role that bacterial surface hydrophobicity (surface tension) plays in determining the extent of adhesion of polymer substrates and phagocytic ingestion is reviewed. The early attachment phase in bacterial adhesion is shown to depend critically on the relative surface tensions of the three interacting phases; i.e., bacteria, substrate, and suspending liquid surface tension. When suspended in a liquid with a high surface tension such as Hanks balanced salt solution, the most hydrophobic bacteria adhere to all surfaces to the greatest extent. When the liquid surface tension (γLV) is larger than the bacterial surface tension (γBV), then for any single bacterial species the extent of adhesion decreases with increasing substrate surface tension (γSV). When γLV < γBV then adhesion increases with increasing γSV. Bacterial surface tension also determines in part the extent of phagocytic ingestion and the degree to which antibodies aspecifically adsorb onto the bacterium resulting in opsonization. The nonspecific adsorption of antibodies results in a considerable modification in the surface properties of the bacteria. Bacterial surface hydrophobicity can be altered significantly through exposure to subinhibitory concentrations of antibiotics, surfactants, lectins, etc. The effect of these changes on subsequent phagocytic ingestion is discussed.
The human antibody response to uropathogenic Escherichia coli: a review
Authors: Salit Irving E. , Hanley James , Clubb Lorraine , Fanning Susan
Published: May 2010

Urinary tract infections caused by Escherichia coli are associated with a local and systemic antibody response. We have studied the serum and urine antibody responses to Escherichia coli in men and women with pyelonephritis, cystitis, and asymptomatic bacteriuria. Protein immunoblots consistently demonstrated serum antibody response to lipopolysaccharide (LPS). Anti-LPS antibody titres rose significantly and progressively when comparing acute with convalescent sera in those who have had their first urinary infection. For those with repeated infections, high titre LPS antibodies were present and did not change significantly between acute and convalescent sera. Antibody responses to the major outer membrane proteins were present but did not differ significantly when compared with normal human serum. A specific anti-P pilus antibody response was demonstrated by immunoblotting. Anti-P pilus antibody was quantitated using ELISA and the titres were found to be very low. Three other techniques were also used to demonstrate the presence of serum antibody. Antibody was detectable by immunofluorescence, but the antigenic specificity of the antibody was more difficult to ascertain. Immunoprecipitation was more specific for determining the nature of the antibody response. Lastly, immunoelectron microscopy was valuable in demonstrating antipilus and antiflagellar antibodies. Immunoelectron microscopy and immunoblotting provided evidence that human antiserum to P pili was modestly cross-reactive and could bind heterologous P pili. These studies indicated that the major antibody response in humans occurs after pyelonephritis and is directed against LPS. An anti-P pilus response is frequently present and is cross-reactive to some extent with other P pili.
Antibiotic efficacy in intraabdominal sepsis: a clinically relevant model
Authors: Bohnen John M. A. , Matlow Anne G. , Mustard Robert A. , Christie Neil A. , Kavouris Bill
Published: May 2010

We present preliminary data on the role of antibiotics in intraabdominal sepsis using a new, clinically relevant animal model. Peritoneal cavity infection was induced by ligation and perforation of the cecum in adult rats. Surviving rats were randomized to receive either saline or cefoxitin at the time of cecal excision and peritoneal lavage, 18 h after the onset of infection. This is different from previous models of abdominal sepsis (in which antibiotics are given within 4 h of peritoneal contamination) and mimics the clinical setting in which antibiotics are initiated much later, at the time of operation. Antibiotic-treated rats received 20 mg cefoxitin i.m. every 8 h for 7 days; controls received saline at similar times. Thirty-nine of 67 control rats died (58%) versus 20 of 64 (31%) that received cefoxitin (p < 0.005). We conclude that even with delayed administration, antibiotics appear to improve the outcome of intraabdominal sepsis. With further characterization of this model we plan to use it as an in vivo assay to compare the efficacy of different antimicrobial agents in intraabdominal sepsis.
Effect of antibiotic treatment on receptivity of uroepithelial ceils to uropathogens
Authors: Reid Gregor , Bruce Andrew W. , Beheshti Mojtaba
Published: May 2010

The management of female patients with recurrent urinary tract infections still remains a problem, and long-term prophylactic or short intermittent courses of antibiotics are the standard forms of therapy. In this report, 10 patients were examined for the effects of long- and short-term treatment with trimethoprim–sulfamethoxazole (TMP–SMX) antibiotics on the receptivity of uroepithelial cells to bacterial adherence. The urine of all patients was sterile while on antibiotic therapy. Few bacteria were found adherent to the cells from adult patients (group 1, mean age 36 years) on long-term antibiotics, but the cells were highly receptive to uropathogens in vitro, especially for Escherichia coli expressing mannose-resistant adhesins. Controls of age-matched adult females were included and in vitro adherence levels were found to be higher for those women with a history of urinary tract infection compared with those with no past record of infection. In the second group, elderly patients (mean age 87 years) presented with bacteriuria, and their uroepithelial cells were found to be colonized by uropathogens to a significantly greater extent than their controls. The adherent population was reduced during 7-day TMP–SMX antibiotic treatment, but increased posttherapy, particularly in two patients who subsequently became reinfected. The in vitro results showed that uroepithelial cells retain their receptivity to uropathogenic adherence, both during and after treatment. Although antibiotics eradicate uropathogens from the urinary tract, patients remain susceptible to recolonization by uropathogens and are at risk of reinfection after completion of therapy.
Bacterial extracellular polysaccharides
Authors: Whitfield Chris
Published: May 2010

The synthesis of extracellular polysaccharides has been recognized in certain bacterial cultures since the 1880s. It is now apparent that a wide range of bacteria produce these polymers and an equally wide range of chemical structures are possible. Their surface location, together with the range of available monosaccharide combinations, noncarbohydrate substituents, and linkage types, make extracellular polysaccharides excellent agents of diversity. As a result, much effort has been directed towards elucidating their structure in pathogenic bacteria and in enteric organisms in particular. Commercial applications of microbial polysaccharides have now broadened the scope of structural information. Most recently, technological advances in molecular biology have created the possibility of manipulating desired polymer characteristics, and with these advances, our knowledge of the mechanisms of synthesis and regulation of cell surface polysaccharides has improved. Ultimately more information regarding the function of extracellular polysaccharides in natural environments may result.
Why can't a cell grow infinitely fast?
Authors: Koch Arthur L.
Published: May 2010

Living cells are esoteric physicochemical systems that have evolved to survive and reproduce in their natural environment. Under balanced conditions of growth, bacteria are probably systems as simple as any kind of free-living organism. Evolutionary forces, seemingly, should have driven prokaryotes to be very efficient. In part that is so; they make effective use of the machinery most expensive for the cell, i.e., the ribosomes and associated factors. But the evidence is that the efficiency with which they use the ribosomal machinery increases as the environment provides more favorable conditions for balanced growth. This article emphasizes the limitation to growth under optimal conditions. The role of fluctuations in the environment and the cost of accurate protein synthesis are discussed as reasons for the upper limit in obtainable specific growth rate.
What is the "true" internal environment of halophilic and other bacteria?
Authors: Kushner Donn J.
Published: May 2010

This article presents facts about, speculations on, and possible ways of determining the actual intracellular ionic environment of halophilic microorganisms and those that live in other extreme conditions. It suggests that halophilic archaebacteria have a truly salty internal environment (though one in which water and salts might well have limited freedom), whereas halophilic and salt-tolerant eubacteria may have salty external environments but much less salty internal ones.
Anaerobic community structure from a nonequilibrium thermodynamic perspective
Authors: McInerney Michael J. , Beaty P. Shawn
Published: May 2010

Thermodynamic analysis of the degradation of selected compounds showed that aerobic and denitrifying processes are heat driven (large enthalpy change). Owing to the smaller enthalpy changes, other anaerobic processes depend more on the entropy flow of chemical substances exchanged with the environment. This results in partial degradation of the substrate and the excretion of end products which have a high free-energy content. This creates niches for organisms to use these end products as energy sources. Mechanistically, the efflux of end products can be used to conserve energy by coupling the efflux with the translocation of protons or other ions. Analysis of published data strongly suggests that the movement of succinate, acetate, and possibly longer chain fatty acids is carrier mediated. Hypothetical calculations showed that these compounds can accumulate to high internal concentrations relative to extracellular concentrations, which suggests that the efflux of these compounds can generate a proton-motive force. This results in the development of mutualistic relationships, where the first species gains additional energy by the continued electrogenic excretion of the end product which enhances the flow of the compound to the second species. Nonequilibrium thermodynamic analysis shows that increasing the flow of materials will favor reactions such as fatty acid degradation which have small changes in free energy.
Adaptive alterations in the outer membrane of gram-negative bacteria during human infection
Authors: Gilleland Jr. H. E.
Published: May 2010

The outer membrane of gram-negative bacteria is a dynamic structure that is capable of altering its ultrastructure and chemistry in order to adapt to changes in its environment. In human infections, outer-membrane alterations are known to play a role in mediating serum resistance, iron uptake, adaptation by Pseudomonas aeruginosa to colonization of the lungs of cystic fibrosis patients, and adaptive resistance to the polymyxin and aminoglycoside antibiotics. This adaptive antibiotic resistance is due to alterations in the cation binding sites within the outer membrane so that these cationic antibiotics can no longer penetrate through the membrane effectively. Adaptive resistance is not stable but is maintained only in the continued presence of the antibiotic. Hence, the role that this type of resistance to cationic antibiotics plays in clinical treatment of human infections remains inadequately assessed.
Adhesion and growth of bacteria at surfaces in oligotrophic habitats
Authors: Marshall Kevin C.
Published: May 2010

In an extension of our previous studies demonstrating the ability of reversibly and irreversibly adhering bacteria to metabolize surface-bound organic substrates, we have directly demonstrated cellular growth and reproduction by previously starved bacteria in association with surface-bound substrates. The mode of cell attachment and division varies with the organisms involved, ranging from a continuous release of daughter cells from a perpendicularly attached mother cell of Vibrio DW1, to normal binary fission and a slow surface migration of face to face attached daughter cells of Pseudomonas JD8, with extensive detachment of cells late in the growth cycle, to normal binary fission in the aqueous phase following surface association of reversibly attached cells of Vibrio MH3. These studies indicate a range of strategies of bacterial growth and development at surfaces.
Aspects of plasmid F maintenance in Escherichia coli
Authors: Kline Bruce C.
Published: May 2010

A major class of replicons in procaryotes is typified by low copy number, nonrandom intracellular distribution, and stable inheritance. Included in this class are chromosomes of gram-positive and gram-negative bacteria as well as a number of plasmids from these organisms. Replicons in this major class have remarkable structural and functional similarities in the genes that effect and control replication. In the present work a review of plasmid F is presented as a paradigm for many aspects of this group's maintenance features.
Use of DNA reassociation in bacterial classification
Authors: Grimont Patrick A. D.
Published: May 2010

The reassociation properties of DNA provide invaluable taxonomic tools. Different methods may give different reassociation values. However, the thermal stability of reassociated DNA strands (a measurement that seems independent of method) is useful in delineating genomic species. Although many phenotypically defined species have been confirmed by DNA reassociation, some medically important genomic species previously had been split into several nomenspecies on the basis of a few characteristics whereas some environmental genomic species had been lumped into unidentifiable aggregates. It might take some time before the nomenclature can be adapted to new taxonomic findings.
Bacterial evolution
Authors: Doolittle W. Ford
Published: May 2010

The deliberate application of the methodology of contemporary molecular genetics to problems in bacterial systematics has lead to a broad new understanding of the evolutionary history of both prokaryotes and eukaryotes. In this review, I discuss some of the major conclusions of this endeavour and try to predict future directions.
Phylogenetic relationships vs. phenotypic diversity: how to achieve a phylogenetic classification system of the eubacteria
Authors: Stackebrandt Erko
Published: May 2010

To establish a hierarchic classification system, ranks cannot be defined by the exclusive and inflexible application of phylogenetic parameters. Because both stability and practicality are prerequisites for a successful system, decisions about the delineation of genera must be made by combining phylogenetic coherency with unifying phenotypic properties of taxonomic value consistent with the needs of a hierarchic system. The phylogenetic depth (age) of a genus has no influence on the decision as long as the members of the genus can be reliably identified as such. The description of those higher taxa that are not easily definable today because of the lack of common phenotypic properties must be postponed until new insights are available. In the end this approach will be both phylogenetic and practical, thus avoiding the use of two classification systems.
A procedure for the study by scanning electron microscopy of flocculating cells of the fission yeast Schizosaccharomyces pombe
Authors: Sowden L. C. , Walker Teena
Published: May 2010

We have investigated a variety of preparative and dehydrating technics in order to examine, by scanning electron microscopy, the cell surface morphology of the fission yeast Schizosaccharomyces pombe, during asexual and sexual flocculation. We found that the loss of the flocculum material surrounding the cell wall was a problem common to many technics. Observations ranged from cells that were covered in varying amounts of hairs, hairlike threads, or a mucilaginous coat to cells so devoid of surface material as to show only well-defined scar regions. The loss of flocculum material is particularly severe with different dehydrating procedures. The method found to provide the best preservation of the cell coat and to produce the most consistent results was double fixation by glutaraldehyde – osmium tetroxide followed by splash–freeze lyophilization. Flocs unfixed, fixed with glutaraldehyde, or stained with uranyl sulfate, and dehydrated followed by critical-point drying or solvent substitution were found to be less satisfactory in the preservation of the cell coat for visualization by scanning electron microscopy.
Further studies of swarmer cell differentiation of Proteus mirabilis PM23: a requirement for iron and zinc
Authors: Jin Tianru , Murray R. G. E.
Published: May 2010

Proteus mirabilis PM23, unlike other motile strains of the species, differentiates in rich fluid media to form nonseptate filaments resembling the swarmer cells formed on solid media. The swarming activity of PM23 is greater than that of the other strains on solid media and it grows faster than another strain, IM47, in differentiation-supporting broth. This faster growth is not exhibited in broth that does not support differentiation. The differentiation of PM23 in brain–heart infusion broth occurs over a wide range of pH and temperature. Inhibitors of swarming on agar plates (p-nitrophenylglycerol and boric acid) and three chelating agents (EDTA, sodium cyanide, and sodium diethyldithiocarbamate) stop differentiation both on plates and in brain–heart infusion broth; however, EGTA is not effective even at 10 mM (10 times the minimum inhibitory concentration of EDTA). The inhibitory mechanisms of p-nitrophenylglycerol and boric acid are different from that of the chelating agents. The timing of EDTA inhibition suggests generation of a "signal" to differentiate after about 2 h growth. Prevention of differentiation by addition of Fe2+ and Zn2+ up to near the time that differentiation should appear suggests that these cations have a crucial involvement in the process of initiation. However, they are not effective as additives in allowing differentiation to occur in defined media or even nutrient broth; the further addition of nucleotides or cAMP was equally ineffective.
A 13C comparative nuclear magnetic resonance study of organic solute production and excretion by the yeasts Hansenula anomala and Saccharomyces cerevisiae in saline media
Authors: Bellinger Yves , Larher François
Published: May 2010

Glycerol, arabitol and trehalose were the principle solutes detected in cellular extracts of Hansenula anomala, using natural-abundance 13C nuclear magnetic resonance spectroscopy. Only the two polyols accumulated in response to increased salinity, glycerol increase being far greater. Arabitol content also increased with culture age, independently of the presence or absence of salt and in line with the evolution of trehalose content. Glycerol retention potential was 15 times greater for Hansenula than for Saccharomyces cerevisiae. The former displayed the specific property of increasing this capacity in high salt concentrations. Under such conditions its growth was associated with a limited increase in glucose consumption per unit biomass, relative to S. cerevisiae, the salt-sensitive reference yeast. In addition, a polysaccharide, the chemical nature of which was not further characterized, was detected exclusively in the external medium of Hansenula growing in the presence of salt.
Immobilization of Acetobacter aceti by adhesion
Authors: Hermesse M. P. , Dereppe C. , Bartholome Y. , Rouxhet P. G.
Published: May 2010

The attachment of three strains of Acetobacter aceti (ATCC 23747, ATCC 23748, NCIB 8246), with or without capsule, cultured under different conditions has been investigated in solutions of controlled pH. Various materials (silicates, organic polymers) have been used as supports, and the results have been related to the surface properties of the cells and supports. Cells that do not have a capsule do not adhere to the tested materials, whatever their hydrophobicity, unless the latter are previously treated by ferric ions to make their surface less negative. Cells that possess a capsule adhere to non-treated supports. In all cases the highest density of the adhering cellular film is obtained when the electrostatic repulsions between a cell and the support and between cells are reduced (surface charge of the support less negative, lower pH). The capsule influences adhesion by affecting the interplay between electrostatic interactions and hydrophobic bonding; moreover, capsule polymers may favor adhesion by acting as binding agent. The occurrence of cell flocculation gives rise to greater heterogeneity and lower cell density in the film of adhering cells.
Factors influencing potent antagonistic effects of Escherichia coli and Bacteroides ovatus on Staphylococcus aureus in anaerobic continuous flow cultures
Authors: Ushijima Tsutomu , Ozaki Yoshikatsu
Published: May 2010

We examined factors related to the potent antagonistic effect of Escherichia coli and Bacteroides ovatus on Staphylococcus aureus in anaerobic continuous flow cultures. In the presence of sugars fermentable by E. coli alone or both E. coli and S. aureus, motile E. coli strains exerted a potent antagonistic effect and S. aureus was expelled from the culture vessel within a few days. Conversely, in the presence of a sugar fermentable by S. aureus alone, the antagonistic effect of E. coli was diminished and S. aureus persisted at ca. 5 × 105 cfu/mL. B. ovatus alone exerted only a weak antagonistic effect on S. aureus in any culture conditions; however, when B. ovatus was cocultivated with E. coli and S. aureus, even in the presence of a sugar fermentable by S. aureus but not by E. coli, the potent antagonistic effect was restored. Escherichia coli showed the same level of antagonistic effect either in the presence of acetic acid (ca. 32 mM), propionic acid (4 mM), butyric acid (17 mM) and hydrogen sulfide(5 × 10−1 mM) or when these metabolic products, except for a small amount of acetic acid (1.2 mM), were not present. In these culture conditions, S. aureus populations were lost at rates much higher than theoretical wash out rates of resting cells. These results indicate the presence of some bactericidal factors other than the volatile fatty acids and hydrogen sulfide. The bactericidal factors were not found in cultures of E. coli heated in boiling water for 10 min and in cell-free culture filtrates. Thus, the bactericidal factors seem to be associated with live E. coli cells. The nature of the bactericidal factors is not clear at present.
Role of protozoa in microbial acclimation for mineralization of organic chemicals in sewage
Authors: Wiggins Bruce A. , Alexander Martin
Published: May 2010

The role of protozoa in affecting the length of the acclimation period for the mineralization of organic compounds in sewage was investigated. The acclimation periods for the mineralization of 2 ng of p-nitrophenol, 100 ng of 2,4-dichlorophenoxyacetic acid, and 100 ng of 2,4-dichlorophenol per milliliter were markedly shortened or eliminated when the indigenous protozoa were inhibited with cycloheximide and nystatin. The extent of mineralization of the test compounds decreased when the protozoa were suppressed. Inhibition of the protozoa increased the total number of bacteria and the density of organisms able to mineralize 2 ng of p-nitrophenol/mL of sewage. Addition of Tetrahymena thermophila to sewage in which the indigenous protozoa were not active lengthened the acclimation period for the mineralization of p-nitrophenol. The addition of T. thermophila to a culture containing a low density of p-nitrophenol-degrading Pseudomonas sp. did not affect the acclimation period prior to mineralization of the substrate, but the ciliate increased the acclimation period in the presence of high densities of Enterobacter aerogenes added as an alternative prey species. We suggest that protozoan grazing may be responsible for the acclimation period prior to the mineralization of certain organic compounds in sewage.
Partial repression of siderophore-mediated iron transport in Azotobacter vinelandii grown with mineral iron
Authors: Page William J. , Grant Gregory A.
Published: May 2010

Azotobacter vinelandii grown in iron-limited medium containing increased amounts of the minerals olivine or glauconite produced decreased amounts of siderophores and iron-repressible outer membrane proteins. These minerals caused a relatively rapid repression of the pyoverdin-type siderophore, azotobactin, and a slower repression of the catechol siderophores, azotochelin and aminochelin. A 77 000 molecular weight outer membrane protein also was repressed with increased mineral content of the medium, but coordinate repression with any one siderophore was not evident. Cells grown with increased mineral concentrations progressively lost siderophore-mediated iron-transport activity. This loss in activity had the greatest effect on azotobactin-mediated 55Fe uptake, but catechol siderophore mediated 55Fe uptake also was depressed. These results suggested that an additional component was required for maximal iron-transport activity promoted by all the siderophores of A. vinelandii.
Effect of valine and the herbicide sulfometuron methyl on acetolactate synthase activity in nuclear and plasmid-borne sulphometuron methyl resistant Saccharomyces cerevisiae strains
Authors: Maiti S. N. , Zink M. W. , Rank G. H.
Published: May 2010

Acetolactate synthase (ALS) specific activity was evaluated in isogenic lines of Saccharomyces cerevisiae carrying the wild-type ILV2 gene or mutations in this gene for resistance to the herbicide sulfometuron methyl (SM). Statistical comparisons were made between two nuclear alleles and among five alleles borne on a YE chimaeric plasmid transformed into a strain carrying a 1.5-kilobase deletion in the nuclear ILV2 gene. Decreased ALS activity of plasmid-borne SM-resistant mutations was shown not to be caused by copy number effects. ALS-specific activity in strains carrying the wild-type ILV2 allele exhibited strong feedback inhibition by valine and was sensitive to SM. All nuclear and plasmid-borne SM-resistance alleles resulted in ALS-specific activity highly resistant to SM and resistant to valine feedback inhibition.
A chromosomal mutation mediating increased expression of pyrE in Salmonella typhimurium is located within the proposed attenuator
Authors: Neuhard J. , Kelln R. A.
Published: May 2010

A chromosomal mutation resulting in 15- to 20-fold increased expression of the Salmonella typhimurium pyrE gene has been cloned and sequenced. The mutation was found to be a single base-pair transition of GC to AT, and occurred within a region of dyad symmetry (attenuator) located just upstream of the pyrE structural gene.