Phylogeny of marine and freshwater Shewanella: reclassification of Shewanella putrefaciens NCIMB 400 as Shewanella frigidimarina.
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Dissimilatory Fe(III) reduction by Shewanella putrefaciens and related species has generated considerable interest in biochemical characterization of the pathways for anaerobic electron transfer in this organism. Two strains, MR-1 and NCIMB 400, have been extensively used, and several respiratory enzymes have been isolated from each. It has become apparent that significant sequence differences exist between homologous proteins from these strains. The 16S rRNA from NCIMB 400 was sequenced and compared to the sequences from MR-1 and other Shewanella strains. The results indicate that NCIMB 400 is significantly more closely related to the newly identified Shewanella frigidimarina than to the S. putrefaciens type strain. It is therefore proposed that NCIMB 400 should be reclassified as S. frigidimarina. (+info)
A cold-active glucanase from the ruminal bacterium Fibrobacter succinogenes S85.
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We previously characterized two endoglucanases, CelG and EGD, from the mesophilic ruminal anaerobe Fibrobacter succinogenes S85. Further comparative experiments have shown that CelG is a cold-active enzyme whose catalytic properties are superior to those of several other intensively studied cold-active enzymes. It has a lower temperature optimum, of 25 degrees C, and retains about 70% of its maximum activity at 0 degrees C, while EGD has a temperature optimum of 35 degrees C and retains only about 18% of its maximal activity at 0 degrees C. When assayed at 4 degrees C, CelG exhibits a 33-fold-higher kcat value and a 73-fold-higher physiological efficiency (kcat/Km) than EGD. CelG has a low thermal stability, as indicated by the effect of temperature on its activity and secondary structure. The presence of small amino acids around the putative catalytic residues may add to the flexibility of the enzyme, thereby increasing its activity at cold temperatures. Its activity is modulated by sodium chloride, with an increase of over 1.8-fold at an ionic strength of 0.03. Possible explanations for the presence of a cold-active enzyme in a mesophile are that cold-active enzymes are more broadly distributed than previously expected, that lateral transfer of the gene from a psychrophile occurred, or that F. succinogenes originated from the marine environment. (+info)
Energy transduction in the sodium F-ATPase of Propionigenium modestum.
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The F-ATPase of the bacterium Propionigenium modestum is driven by an electrochemical sodium gradient between the cell interior and its environment. Here we present a mechanochemical model for the transduction of transmembrane sodium-motive force into rotary torque. The same mechanism is likely to operate in other F-ATPases, including the proton-driven F-ATPases of Escherichia coli. (+info)
Interactions between carbon and nitrogen metabolism in Fibrobacter succinogenes S85: a 1H and 13C nuclear magnetic resonance and enzymatic study.
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The effect of the presence of ammonia on [1-13C]glucose metabolism in the rumen fibrolytic bacterium Fibrobacter succinogenes S85 was studied by 13C and 1H nuclear magnetic resonance (NMR). Ammonia halved the level of glycogen storage and increased the rate of glucose conversion into acetate and succinate 2.2-fold and 1.4-fold, respectively, reducing the succinate-to-acetate ratio. The 13C enrichment of succinate and acetate was precisely quantified by 13C-filtered spin-echo difference 1H-NMR spectroscopy. The presence of ammonia did not modify the 13C enrichment of succinate C-2 (without ammonia, 20.8%, and with ammonia, 21.6%), indicating that the isotopic dilution of metabolites due to utilization of endogenous glycogen was not affected. In contrast, the presence of ammonia markedly decreased the 13C enrichment of acetate C-2 (from 40 to 31%), reflecting enhanced reversal of the succinate synthesis pathway. The reversal of glycolysis was unaffected by the presence of ammonia as shown by 13C-NMR analysis. Study of cell extracts showed that the main pathways of ammonia assimilation in F. succinogenes were glutamate dehydrogenase and alanine dehydrogenase. Glutamine synthetase activity was not detected. Glutamate dehydrogenase was active with both NAD and NADP as cofactors and was not repressed under ammonia limitation in the culture. Glutamate-pyruvate and glutamate-oxaloacetate transaminase activities were evidenced by spectrophotometry and 1H NMR. When cells were incubated in vivo with [1-13C]glucose, only 13C-labeled aspartate, glutamate, alanine, and valine were detected. Their labelings were consistent with the proposed amino acid synthesis pathway and with the reversal of the succinate synthesis pathway. (+info)
Phylogenetic analysis of Formivibrio citricus, Propionivibrio dicarboxylicus, Anaerobiospirillum thomasii, Succinimonas amylolytica and Succinivibrio dextrinosolvens and proposal of Succinivibrionaceae fam. nov.
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The phylogenetic position of Gram-negative, strictly anaerobic, non-spore-forming bacteria, representing four different genera, was determined by analysis of their 16S rDNA sequences. Formivibrio citricus and Propionivibrio dicarboxylicus are members of the beta-subclass of the class Proteobacteria. While Formivibrio citricus stands phylogenetically isolated, Propionivibrio dicarboxylicus is moderately related to members of the genus Rhodocyclus. Succinimonas amylolytica and Succinivibrio dextrinosolvens are members of the gamma-subclass of the class Proteobacteria in which they, together with members of the genus Anaerobiospirillum and Ruminobacter amylophilus, form a separate line of descent. This phylogenetic group is described as Succinivibrionaceae fam. nov. (+info)
Microbial communities associated with anaerobic benzene degradation in a petroleum-contaminated aquifer.
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Microbial community composition associated with benzene oxidation under in situ Fe(III)-reducing conditions in a petroleum-contaminated aquifer located in Bemidji, Minn., was investigated. Community structure associated with benzene degradation was compared to sediment communities that did not anaerobically oxidize benzene which were obtained from two adjacent Fe(III)-reducing sites and from methanogenic and uncontaminated zones. Denaturing gradient gel electrophoresis of 16S rDNA sequences amplified with bacterial or Geobacteraceae-specific primers indicated significant differences in the composition of the microbial communities at the different sites. Most notable was a selective enrichment of microorganisms in the Geobacter cluster seen in the benzene-degrading sediments. This finding was in accordance with phospholipid fatty acid analysis and most-probable-number-PCR enumeration, which indicated that members of the family Geobacteraceae were more numerous in these sediments. A benzene-oxidizing Fe(III)-reducing enrichment culture was established from benzene-degrading sediments and contained an organism closely related to the uncultivated Geobacter spp. This genus contains the only known organisms that can oxidize aromatic compounds with the reduction of Fe(III). Sequences closely related to the Fe(III) reducer Geothrix fermentans and the aerobe Variovorax paradoxus were also amplified from the benzene-degrading enrichment and were present in the benzene-degrading sediments. However, neither G. fermentans nor V. paradoxus is known to oxidize aromatic compounds with the reduction of Fe(III), and there was no apparent enrichment of these organisms in the benzene-degrading sediments. These results suggest that Geobacter spp. play an important role in the anaerobic oxidation of benzene in the Bemidji aquifer and that molecular community analysis may be a powerful tool for predicting a site's capacity for anaerobic benzene degradation. (+info)
Beta-lactamase production by oral anaerobic gram-negative species in infants in relation to previous antimicrobial therapy.
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The frequency of beta-lactamase production in gram-negative bacteria has increased considerably during recent years. In this study, beta-lactamase production by oral anaerobic gram-negative rods isolated from saliva was longitudinally examined for 44 Caucasian infants at the ages of 2, 6, and 12 months in relation to their documented exposure to antibiotics. Isolates showing decreased susceptibility to penicillin G (1 microg/ml) were examined for beta-lactamase production by using a chromogenic cephalosporin disk test. beta-Lactamase-positive, gram-negative anaerobic species were found in 11, 55, and 89% of each age group, respectively. beta-Lactamase production was most frequent among organisms of the Prevotella melaninogenica group. At 12 months, 73% of the infants harbored beta-lactamase-producing members of the P. melaninogenica group, 55% had nonpigmented Prevotella species, 25% had Porphyromonas catoniae, 23% had Fusobacterium nucleatum, and 5% had Capnocytophaga species. Several beta-lactamase-producing species could be simultaneously found in the infants' mouths. The presence of beta-lactamase-producing species was significantly associated with the infants' exposure to antibiotics through antimicrobial treatments given to the infants and/or their mothers. (+info)
The effects of three nonoxynol-9 preparations on vaginal flora and epithelium.
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To evaluate the effects of nonoxynol-9 (N-9) on the vaginal flora and epithelium, 48 women (16 in each group) were evaluated by use of quantitative vaginal cultures and colposcopy. at baseline and at 0.5, 4, 24, 48, and 72 h after insertion of one of three N-9 preparations (4% gel [Conceptrol], 3.5% gel [Advantage-24], or a 28% vaginal contraceptive film). The proportion positive for H2O2+ or H2O2- lactobacilli did not change significantly with any of the preparations, but lactobacilli concentrations decreased transiently. Both the proportion of women with Gardnerella vaginalis and the concentration of G. vaginalis decreased transiently. The proportion of women with Escherichia coli increased with the 4% gel, and the concentration increased with all preparations. The number with anaerobic gram-negative rods increased, although the concentrations decreased. Symptoms and colposcopic abnormalities were rare. Changes in levels of vaginal bacteria were transient after single applications of N-9, but adverse effects may be enhanced with frequent, chronic use. (+info)