bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sulfate-Reducing Bacteria Methylate Mercury at Variable Rates in Pure Culture and in Marine Sediments
Authors: King Jeffrey K. , Kostka Joel E. , Frischer Marc E. , Saunders F. Michael 
Published: July 2002

ABSTRACT

Differences in methylmercury (CH
3
Hg) production normalized to the sulfate reduction rate (SRR) in various species of sulfate-reducing bacteria (SRB) were quantified in pure cultures and in marine sediment slurries in order to determine if SRB strains which differ phylogenetically methylate mercury (Hg) at similar rates. Cultures representing five genera of the SRB (
Desulfovibrio desulfuricans
,
Desulfobulbus propionicus
,
Desulfococcus multivorans
,
Desulfobacter
sp. strain BG-8, and
Desulfobacterium
sp. strain BG-33) were grown in a strictly anoxic, minimal medium that received a dose of inorganic Hg 120 h after inoculation. The mercury methylation rates (MMR) normalized per cell were up to 3 orders of magnitude higher in pure cultures of members of SRB groups capable of acetate utilization (e.g., the family
Desulfobacteriaceae
) than in pure cultures of members of groups that are not able to use acetate (e.g., the family
Desulfovibrionaceae
). Little or no Hg methylation was observed in cultures of
Desulfobacterium
or
Desulfovibrio
strains in the absence of sulfate, indicating that Hg methylation was coupled to respiration in these strains. Mercury methylation, sulfate reduction, and the identities of sulfate-reducing bacteria in marine sediment slurries were also studied. Sulfate-reducing consortia were identified by using group-specific oligonucleotide probes that targeted the 16S rRNA molecule. Acetate-amended slurries, which were dominated by members of the
Desulfobacterium
and
Desulfobacter
groups, exhibited a pronounced ability to methylate Hg when the MMR were normalized to the SRR, while lactate-amended and control slurries had normalized MMR that were not statistically different. Collectively, the results of pure-culture and amended-sediment experiments suggest that members of the family
Desulfobacteriaceae
have a greater potential to methylate Hg than members of the family
Desulfovibrionaceae
have when the MMR are normalized to the SRR. Hg methylation potential may be related to genetic composition and/or carbon metabolism in the SRB. Furthermore, we found that in marine sediments that are rich in organic matter and dissolved sulfide rapid CH
3
Hg accumulation is coupled to rapid sulfate reduction. The observations described above have broad implications for understanding the control of CH
3
Hg formation and for developing remediation strategies for Hg-contaminated sediments.
Cellulose Catabolism by
Clostridium cellulolyticum
Growing in Batch Culture on Defined Medium
Authors: Desvaux Mickaël , Guedon Emmanuel , Petitdemange Henri 
Published: July 2002

ABSTRACT

A reinvestigation of cellulose degradation by
Clostridium cellulolyticum
in a bioreactor with pH control of the batch culture and using a defined medium was performed. Depending on cellulose concentration, the carbon flow distribution was affected, showing the high flexibility of the metabolism. With less than 6.7 g of cellulose liter
−1
, acetate, ethanol, H
2
, and CO
2
were the main end products of the fermentation and cellulose degradation reached more than 85% in 5 days. The electron flow from the glycolysis was balanced by the production of H
2
and ethanol, the latter increasing with increasing initial cellulose concentration. From 6.7 to 29.1 g of cellulose liter
−1
, the percentage of cellulose degradation declined; most of the cellulase activity remained on the cellulose fibers, the maximum cell density leveled off, and the carbon flow was reoriented from ethanol to acetate. In addition to that of previously indicated end products, lactate production rose, and, surprisingly enough, pyruvate overflow occurred. Concomitantly the molar growth yield and the energetic yield of the biomass decreased. Growth arrest may be linked to sufficiently high carbon flow, leading to the accumulation of an intracellular inhibitory compound(s), as observed on cellobiose (E. Guedon, M. Desvaux, S. Payot, and H. Petitdemange, Microbiology 145:1831–1838, 1999). These results indicated that bacterial metabolism exhibited on cellobiose was distorted compared to that exhibited on a substrate more closely related to the natural ecosystem of
C. cellulolyticum
. To overcome growth arrest and to improve degradation at high cellulose concentrations (29.1 g liter
−1
), a reinoculation mode was evaluated. This procedure resulted in an increase in the maximum dry weight of cells (2,175 mg liter
−1
), cellulose solubilization (95%), and end product concentrations compared to a classical batch fermentation with a final dry weight of cells of 580 mg liter
−1
and 45% cellulose degradation within 18 days.
Influence of Sulfide and Temperature on Species Composition and Community Structure of Hot Spring Microbial Mats
Authors: Skirnisdottir Sigurlaug , Hreggvidsson Gudmundur O. , Hjörleifsdottir Sigridur , Marteinsson Viggo T. , Petursdottir Solveig K. , Holst Olle , Kristjansson Jakob K. 
Published: July 2002

ABSTRACT

In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80°C that are white or yellow from precipitated sulfur (sulfur mats). In low-sulfide hot springs in the same area, grey or pink streamers are formed at 80 to 90°C, and a
Chloroflexus
mat is formed at 65 to 70°C. We have studied the microbial diversity of one sulfur mat (high-sulfide) hot spring and one
Chloroflexus
mat (low-sulfide) hot spring by cloning and sequencing of small-subunit rRNA genes obtained by PCR amplification from mat DNA. Using 98% sequence identity as a cutoff value, a total of 14 bacterial operational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the sulfur mat; 18 bacterial OTUs were detected in the
Chloroflexus
mat. Although representatives of novel divisions were found, the majority of the sequences were >95% related to currently known sequences. The molecular diversity analysis showed that
Chloroflexus
was the dominant mat organism in the low-sulfide spring (1 mg liter
−1
) below 70°C, whereas
Aquificales
were dominant in the high-sulfide spring (12 mg liter
−1
) at the same temperature. Comparison of the present data to published data indicated that there is a relationship between mat type and composition of
Aquificales
on the one hand and temperature and sulfide concentration on the other hand.
Bioaugmentation of Activated Sludge by an Indigenous 3-Chloroaniline-Degrading
Comamonas testosteroni
Strain, I2
gfp
Authors: Boon Nico , Goris Johan , De Vos Paul , Verstraete Willy , Top Eva M. 
Published: July 2002

ABSTRACT

A strain identified as
Comamonas testosteroni
I2 was isolated from activated sludge and found to be able to mineralize 3-chloroaniline (3-CA). During the mineralization, a yellow intermediate accumulated temporarily, due to the distal
meta
-cleavage of chlorocatechol. This strain was tested for its ability to clean wastewater containing 3-CA upon inoculation into activated sludge. To monitor its survival, the strain was chromosomally marked with the
gfp
gene and designated I2
gfp
. After inoculation into a lab-scale semicontinuous activated-sludge (SCAS) system, the inoculated strain maintained itself in the sludge for at least 45 days and was present in the sludge flocs. After an initial adaptation period of 6 days, complete degradation of 3-CA was obtained during 2 weeks, while no degradation at all occurred in the noninoculated control reactor. Upon further operation of the SCAS system, only 50% 3-CA removal was observed. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes revealed a dynamic change in the microbial community structure of the activated sludge. The DGGE patterns of the noninoculated and the inoculated reactors evolved after 7 days to different clusters, which suggests an effect of strain inoculation on the microbial community structure. The results indicate that bioaugmentation, even with a strain originating from that ecosystem and able to effectively grow on a selective substrate, is not permanent and will probably require regular resupplementation.
Engineering of the Pyruvate Dehydrogenase Bypass inSaccharomyces cerevisiae: Role of the Cytosolic Mg2+and Mitochondrial K+Acetaldehyde Dehydrogenases Ald6p and Ald4p in Acetate Formation during Alcoholic Fermentation
Authors: Remize Fabienne , Andrieu Emilie , Dequin Sylvie 
Published: July 2002

ABSTRACTAcetic acid plays a crucial role in the organoleptic balance of many fermented products. We have investigated the factors controlling the production of acetate bySaccharomyces cerevisiaeduring alcoholic fermentation by metabolic engineering of the enzymatic steps involved in its formation and its utilization. The impact of reduced pyruvate decarboxylase (PDC), limited acetaldehyde dehydrogenase (ACDH), or increased acetoacetyl coenzyme A synthetase (ACS) levels in a strain derived from a wine yeast strain was studied during alcoholic fermentation. In the strain with thePDC1gene deleted exhibiting 25% of the PDC activity of the wild type, no significant differences were observed in the acetate yield or in the amounts of secondary metabolites formed. A strain overexpressingACS2and displaying a four- to sevenfold increase in ACS activity did not produce reduced acetate levels. In contrast, strains with one or two disrupted copies ofALD6, encoding the cytosolic Mg2+-activated NADP-dependent ACDH and exhibiting 60 and 30% of wild-type ACDH activity, showed a substantial decrease in acetate yield (the acetate production was 75 and 40% of wild-type production, respectively). This decrease was associated with a rerouting of carbon flux towards the formation of glycerol, succinate, and butanediol. The deletion ofALD4, encoding the mitochondrial K+-activated NAD(P)-linked ACDH, had no effect on the amount of acetate formed. In contrast, a strain lacking both Ald6p and Ald4p exhibited a long delay in growth and acetate production, suggesting that Ald4p can partially replace the Ald6p isoform. Moreover, theald6 ald4double mutant was still able to ferment large amounts of sugar and to produce acetate, suggesting the contribution of another member(s) of theALDfamily.
Light and the Transcriptional Response of the Microcystin Biosynthesis Gene Cluster
Authors: Kaebernick Melanie , Neilan Brett A. , Börner Thomas , Dittmann Elke 
Published: July 2002

ABSTRACTMicrocystin, a hepatotoxin known to be the cause of animal and human deaths, is produced by the bloom-forming cyanobacteriumMicrocystis aeruginosain freshwater bodies worldwide. The toxin is produced nonribosomally via a multifunctional enzyme complex, consisting of both peptide synthetase and polyketide synthase modules coded for by themcygene cluster. The recent identification of themcygenes in the production of microcystin synthetase for the first time provides an avenue to study the regulation of microcystin production at a genetic level. In this study,M. aeruginosaPCC7806 was grown either under continuous light of various intensities or under low light with subsequent short-term exposure to different light intensities and qualities and various stress factors. RNase protection assays were employed to observe the level ofmcyBandmcyDtranscription under each condition. BothmcyBandmcyDtranscript levels were increased under high light intensities and red light. Blue light and certain artificial stress factors (methylviologen and NaCl) led to reduced transcript amounts. There appeared to be two light thresholds, between dark and low light (16 μmol of photons m−2s−1), and medium (31 μmol of photons m−2s−1) and high light (68 μmol of photons m−2s−1), at which a significant increase in transcription occurred. Our findings show that the effect of light on microcystin synthetase production is due to light quality and is initiated at certain threshold intensities, which are not necessarily reflected by observed intracellular toxin bioactivity.
Effect of Field Inoculation with
Sinorhizobium meliloti
L33 on the Composition of Bacterial Communities in Rhizospheres of a Target Plant (
Medicago sativa
) and a Non-Target Plant (
Chenopodium album
)—Linking of 16S rRNA Gene-Based Single-Strand Conformation Polymorphism Community Profiles to the Diversity of Cultivated Bacteria
Authors: Schwieger Frank , Tebbe Christoph C. 
Published: July 2002

ABSTRACT

Fourteen weeks after field release of luciferase gene-tagged
Sinorhizobium meliloti
L33 in field plots seeded with
Medicago sativa
, we found that the inoculant also occurred in bulk soil from noninoculated control plots. In rhizospheres of
M. sativa
plants,
S. meliloti
L33 could be detected in noninoculated plots 12 weeks after inoculation, indicating that growth in the rhizosphere preceded spread into bulk soil. To determine whether inoculation affected bacterial diversity, 1,119 bacteria were isolated from the rhizospheres of
M. sativa
and
Chenopodium album
, which was the dominant weed in the field plots. Amplified ribosomal DNA restriction analysis (ARDRA) revealed plant-specific fragment size frequencies. Dominant ARDRA groups were identified by 16S rRNA gene nucleotide sequencing. Database comparisons indicated that the rhizospheres contained members of the
Proteobacteria
(α, β, and γ subgroups), members of the
Cytophaga-Flavobacterium
group, and gram-positive bacteria with high G+C DNA contents. The levels of many groups were affected by the plant species and, in the case of
M. sativa
, by inoculation. The most abundant isolates were related to
Variovorax
sp.,
Arthrobacter ramosus
, and
Acinetobacter calcoaceticus
. In the rhizosphere of
M. sativa
, inoculation reduced the numbers of cells of
A. calcoaceticus
and members of the genus
Pseudomonas
and increased the number of rhizobia. Cultivation-independent PCR–single-strand conformation polymorphism (SSCP) profiles of a 16S rRNA gene region confirmed the existence of plant-specific rhizosphere communities and the effect of the inoculant. All dominant ARDRA groups except
Variovorax
species could be detected. On the other hand, the SSCP profiles revealed products which could not be assigned to the dominant cultured isolates, indicating that the bacterial diversity was greater than the diversity suggested by cultivation.
Purification and Characterization of an Extracellular Poly(
l
-Lactic Acid) Depolymerase from a Soil Isolate,
Amycolatopsis
sp. Strain K104-1
Authors: Nakamura Kohei , Tomita Toshio , Abe Naoki , Kamio Yoshiyuki 
Published: July 2002

ABSTRACT

Poly(
l
-lactic acid) (PLA)-degrading
Amycolatopsis
sp. strains K104-1 and K104-2 were isolated by screening 300 soil samples for the ability to form clear zones on the PLA-emulsified mineral agar plates. Both of the strains assimilated >90% of emulsified 0.1% (wt/vol) PLA within 8 days under aerobic conditions. A novel PLA depolymerase with a molecular weight of 24,000 was purified to homogeneity from the culture supernatant of strain K104-1. The purified enzyme degraded high-molecular-weight PLA in emulsion and in solid film, ultimately forming lactic acid. The optimum pH for the enzyme activity was 9.5, and the optimum temperature was 55 to 60°C. The PLA depolymerase also degraded casein and fibrin but did not hydrolyze collagen type I, triolein, tributyrin, poly(β-hydroxybutyrate), or poly(ε-caprolactone). The PLA-degrading and caseinolytic activities of the enzyme were inhibited by diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride but were not significantly affected by soybean trypsin inhibitor,
N
-tosyl-
l
-lysyl chloromethyl ketone,
N
-tosyl-
l
-phenylalanyl chloromethyl ketone, and
Streptomyces
subtilisin inhibitor. Thus,
Amycolatopsis
sp. strain K104-1 excretes the unique PLA-degrading and fibrinolytic serine enzyme, utilizing extracellular polylactide as a sole carbon source.
Surface Interactions between
Escherichia coli
and Hemocytes of the Mediterranean Mussel
Mytilus galloprovincialis
Lam. Leading to Efficient Bacterial Clearance
Authors: Canesi Laura , Pruzzo Carla , Tarsi Renato , Gallo Gabriella 
Published: July 2002

ABSTRACT

The role of type 1 fimbriae in the interactions between
Escherichia coli
and
Mytilus galloprovincialis
Lam. hemocytes was evaluated. The association of fimbriated strain MG155 with hemocyte monolayers at 18°C was 1.5- and 3- to 4-fold greater than the association of unfimbriated mutant AAEC072 in artificial seawater and in hemolymph serum, respectively. Such differences were apparently due to different adhesive properties since MG155 adhered more efficiently than AAEC072 when hemocytes were incubated at 4°C to inhibit the internalization process. Hemolymph serum increased both association and adherence of MG155 two- to threefold but did not affect association and adherence of AAEC072. MG155 was also 1.5- to 1.7-fold more sensitive to killing by hemocytes than AAEC072, as evaluated by the number of culturable bacteria after 60 and 120 min of incubation. The role of type 1 fimbriae in MG155 interactions with hemocytes was confirmed by the inhibitory effect of
d
-mannose. In in vivo experiments MG155 cells were cleared from circulating hemolymph more rapidly than AAEC072 cells were cleared. These results confirm that surface properties are crucial in influencing bacterial persistence and survival within mussel hemolymph.
pH Signaling in
Sclerotinia sclerotiorum
: Identification of a
pacC/RIM1
Homolog
Authors: Rollins Jeffrey A. , Dickman Martin B. 
Published: July 2002

ABSTRACT

Sclerotinia sclerotiorum
acidifies its ambient environment by producing oxalic acid. This production of oxalic acid during plant infection has been implicated as a primary determinant of pathogenicity in this and other phytopathogenic fungi. We found that ambient pH conditions affect multiple processes in
S. sclerotiorum
. Exposure to increasing alkaline ambient pH increased the oxalic acid accumulation independent of carbon source, sclerotial development was favored by acidic ambient pH conditions but inhibited by neutral ambient pH, and transcripts encoding the endopolygalacturonase gene
pg1
accumulated maximally under acidic culture conditions. We cloned a putative transcription factor-encoding gene,
pac1
, that may participate in a molecular signaling pathway for regulating gene expression in response to ambient pH. The three zinc finger domains of the predicted Pac1 protein are similar in sequence and organization to the zinc finger domains of the
A. nidulans
pH-responsive transcription factor PacC. The promoter of
pac1
contains eight PacC consensus binding sites, suggesting that this gene, like its homologs, is autoregulated. Consistent with this suggestion, the accumulation of
pac1
transcripts paralleled increases in ambient pH. Pac1 was determined to be a functional homolog of PacC by complementation of an
A. nidulans pacC
-null strain with
pac1
. Our results suggest that ambient pH is a regulatory cue for processes linked to pathogenicity, development, and virulence and that these processes may be under the molecular regulation of a conserved pH-dependent signaling pathway analogous to that in the nonpathogenic fungus
A. nidulans
.
Various Levels of Cross-Resistance to
Bacillus sphaericus
Strains in
Culex pipiens
(Diptera: Culicidae) Colonies Resistant to
B. sphaericus
Strain 2362
Authors: Nielsen-LeRoux Christina , Rao D. Raghunatha , Murphy Jittawadee Rodcharoen , Carron Alexandre , Mani T. R. , Hamon Sylviane , Mulla Mir S. 
Published: July 2002

ABSTRACT

We studied the cross-resistance to three highly toxic
Bacillus sphaericus
strains, IAB-59 (serotype H6), IAB-881 (serotype H3), and IAB-872 (serotype H48), of four colonies of the
Culex pipiens
complex resistant to
B. sphaericus
2362 and 1593, both of which are serotype H5a5b strains. Two field-selected highly resistant colonies originating from India (KOCHI, 17,000-fold resistance) and France (SPHAE, 23,000-fold resistance) and a highly resistant laboratory-selected colony from California (GeoR, 36,000-fold resistance) showed strong cross-resistance to strains IAB-881 and IAB-872 but significantly weaker cross-resistance to IAB-59 (3- to 43-fold resistance). In contrast, a laboratory-selected California colony with low-level resistance (JRMM-R, 5-fold resistance) displayed similar levels of resistance (5- to 10-fold) to all of the
B. sphaericus
strains tested. Thus, among the mosquitocidal strains of
B. sphaericus
we identified a strain, IAB-59, which was toxic to several
Culex
colonies that were highly resistant to commercial strains 2362 and 1593. Our analysis also indicated that strain IAB-59 may possess other larvicidal factors. These results could have important implications for the development of resistance management strategies for area-wide mosquito control programs based on the use of
B. sphaericus
preparations.
Identification and Characterization of the Three Chitin-Binding Domains within the Multidomain Chitinase Chi92 from
Aeromonas hydrophila
JP101
Authors: Wu Mei Li , Chuang Yin Ching , Chen Jen Pin , Chen Chin Shuh , Chang Ming Chung 
Published: July 2002

ABSTRACT

The gene (
chi92
) encoding the extracellular chitinase of
Aeromonas hydrophila
JP101 has been cloned and expressed in
Escherichia coli
. The mature form of Chi92 is an 842-amino-acid (89.830-kDa) modular enzyme comprised of a family 18 catalytic domain, an unknown-function region (the A region), and three chitin-binding domains (ChBDs; Chi92-N, ChBD
CI
, and ChBD
CII
). The C-terminally repeated ChBDs, ChBD
CI
and ChBD
CII
, were grouped into family V of cellulose-binding domains on the basis of sequence homology. Chitin binding and enzyme activity studies with C-terminally truncated Chi92 derivatives lacking ChBDs demonstrated that the ChBDs are responsible for its adhesion to unprocessed and colloidal chitins. Further adsorption experiments with glutathione
S
-transferase (GST) fusion proteins (GST-CI and GST-CICII) demonstrated that a single ChBD (ChBD
CI
) could promote efficient chitin and cellulose binding. In contrast to the two C-terminal ChBDs, the Chi92-N domain is similar to ChiN of
Serratia marcescens
ChiA, which has been proposed to participate in chitin binding. A truncated derivative of Chi92 that contained only a catalytic domain and Chi92-N still exhibited insoluble-chitin-binding and hydrolytic activities. Thus, it appears that Chi92 contains Chi92-N as the third ChBD in addition to two ChBDs (ChBD
CI
and ChBD
CII
).