The contamination of soil and wastewaters with Cr(VI) is a major problem. It has been suggested that microbial methods for Cr(VI) reduction are better than chemical methods, as they do not add other ions or toxic chemicals to the environment. In this study an aerobic reduction of Cr(VI) to Cr(III) by employing mixed Pseudomonas cultures isolated from a marshy land has been reported. The role of chromium concentration, temperature, pH and additives on the microbial reduction of Cr(VI) has been investigated. NADH was found to enhance the rate of reduction of Cr(VI). Complete reduction of chromium(VI) has been possible even at chromium(VI) concentrations of 300 ppm. Ions like SO42− and poly-phenols inhibited the metabolic activity relating to Cr(VI) reduction. Under optimal conditions 100 mg/L of Cr(VI) was completely reduced within 180 min.
YtvA of Bacillus subtilis consists of light, oxygen or voltage (LOV) domain and sulfate transporter and anti-sigma antagonist (STAS) domain, and was reported to act as a photoreceptor, sensing light signals through the LOV domain, like a plant blue light receptor, phototropin. At the same time, YtvA was reported to act as a positive regulator for stress responsive-gene expression regulated by σB factor. Here we indicate that, like phototropins, the conserved Cys residue among the LOV domains is required for light-sensing in YtvA in vitro, possibly by the photoadduct formation, and YtvA forms a homodimer via its LOV domain, independently to light signal. We also indicate that, when ytvA expression is in normal level, light itself does not trigger σB activation, but a photo-enhancement of σB activity, activated by salt stress, occurs only in the presence of ytvA. The conserved Cys residue in the LOV domain and the STAS domain seem to be responsible for light-sensing and signal-transmission to the σB regulatory network, respectively.
Three genes, sigF, sigG and sigH, encoding group 3 sigma factors have been cloned and characterized in the marine cyanobacterium Synechococcus sp. strain PCC 7002. The sigF gene product was similar to sigma factors involved in general stress response and sporulation in other organisms, and the sigG and sigH gene products were similar to extracytoplasmic function (ECF) sigma factors. The sigG and sigH genes were associated with the putative regulatory genes and the sizes of transcripts for sigG and sigH genes were large enough to be cotranscribed with the associated downstream genes. The sigG downstream gene was designated sapG (sigG-associated protein), and yeast two-hybrid analysis demonstrated that SigG and SapG interact when produced in yeast cells. Null mutants of these three group 3 sigma factor genes were created by interposon mutagenesis. The growth of the sigF mutant strain was much slower than the wild-type strain at 15°C, although the growth rates at 22°C and 38°C were identical to those of the wild-type strain. The sigG mutant could not grow continuously at 22°C, and no growth occurred at 15°C. Since SigG and SapG interact in yeast cells and the sigG and sapG mutants showed a similar growth phenotype, SapG is likely to be a regulatory protein for SigG involved in the same pathway in transcriptional regulation in this cyanobacterium.
Biopolymer (polyhydroxyalkanoate, PHA) was extracted and purified from CMG607w bacterial strain isolated from sediment of Layari River outfall to the Arabian Sea. Synthesis of PHA was substrate depended in CMG607w. In the presence of sodium gluconate mcl-PHA was synthesized at the rate of 42% cell dry mass. Under highly enriched conditions, co-production of polysaccharide and blends of poly(3-hydroxybutyrate) (PHB)/PHA was observed. PCR base strategy was used to amplify PHA polymerase genes from chromosomal DNA. Conserved sequences were observed in polymeraseC1 and C2. A portion of polymerase C1 and C2 genes of the pha operon was cloned and sequenced. In CMG607w PHA biosynthsis the operon has phaC1 and C2 (polymerase 1 and polymerase 2) genes. pha polymerase C1/C2 genes of CMG607w have 98% homology to Pseudomonas aeruginosa PAO1 (AE004919). Gene sequences were submitted to GenBank under accession numbers EF028075, AY596788 and AY596790.
This study was carried out to screen lactic acid bacteria that produce active dietary enzymes, such as amylase, lipase, phytase, and protease, using a two-step process in pigs. We isolated a total of 210 and 132 strains of bacteria, grown under aerobic and anaerobic conditions, respectively, in Man Rogosa Sharpe agar containing 0.13% bile after treatment of intestinal samples at pH 3 for 30 min. From fecal samples, a total of 134 aerobic and 111 anaerobic strains were isolated in the same manner. In the second screening test, we selected four strains that produced four dietary enzymes from isolates obtained in the first screening test. Each strain was characterized as lactobacilli based on the following criteria: rod shape, negative for catalase, Gram positive, and lack of acute oral toxicity in mice. Of these four strains, we finally selected Lactobacillus spp. PSC101, which was resistant to pH 3 for 8 h and grew in the presence of 1% bile. In summary, Lactobacillus sp. PSC101 may be a strong probiotic candidate in swine due to its resistance to both acid and bile, its production of dietary enzymes that promote animal growth, and its non-toxic nature in mice.
Two different isolation methods, the dilution colony-counting method (colony-isolation) and enrichment culture, were used to isolate sulfate-reducing bacteria (SRBs) from estuarine sediment in Japan. Lactate was used as an electron donor for colony-isolation, and lactate or propionate was used for enrichment culture. All isolates were classified into six different phylogenetic groups according to the 16S rRNA gene-based analysis. The closest relatives of the colony-isolates (12 strains) were species in the genera of Desulfobacterium, Desulfofrigus, Desulfovibrio and Desulfomicrobium. The closest known relative of the lactate-enrichment isolates was Desulfovibrio acrylicus and that of the propionate-enrichment isolates was Desulfobulbus mediterraneus. All isolates were incompletely-oxidizing SRBs. Overall patterns of utilization of electron donors and acceptors, as well as fermentative substrates, differed depending on the affiliation of the strain. Furthermore, even if several strains used the same substrate, the growth rates were often significantly different depending on the strain. It was strongly suggested that various species of SRBs could coexist in the sediment by competing for common substrates as well as taking priority in favorable or specific substrates for each species and the community of SRBs should be able to oxidize almost all major intermediates of anaerobic decomposition of organic matter such as lower fatty acids, alcohols and H2 as well as amino acids. Thus, it was indicated by the phylogenetic and physiological analyses of the isolates that the SRB community composed of diverse lineages of bacteria living in anoxic estuarine sediment should be able to play an extensive role in the carbon cycle as well as the sulfur cycle of the earth.
Forty-four Thai isolates phenotypically assigned to the genus Gluconobacter were examined for 16S-23S rDNA ITS restriction analysis by MboII and SduI (=Bsp1286I) digestions. The Thai isolates tested were divided into seven groups: Group I for fourteen isolates, Group IX for one isolate, Group X for two isolates, Group V-2 for four isolates, Group XI for three isolates, Group IV for one isolate, and Group III for nineteen isolates. There were no isolates of either Group II or Group V-1 that were identified as G. cerinus. The isolates of Group III, Group IV, and Group XI were subjected to an additional 16S-23S rDNA ITS restriction analysis by AvaII, TaqI, BsoBI, and BstNI digestions. The isolates of Group III were divided into three groups and two subgroups: Group III-2 for five isolates, Group III-6 for two isolates, and Group III-4, which was divided into two subgroups, Subgroup III-4a for four isolates and Subgroup III-4b for eight isolates. The fourteen isolates of Group I were identified as G. oxydans, and the two isolates of Group X were temporarily identified as G. oxydans. The five isolates of Group III-2 and the one isolate of Group IV were identified as G. frateurii. The remaining twenty-two isolates of Group V-2, Group III-4, Group III-6, Group IX, and Group XI were not identified but are candidates for several new species.
An Escherichia colipgsA null mutant deficient in acidic phospholipids shows a thermosensitive cell lysis phenotype because of activation of the Rcs phosphorelay signal transduction system. We conducted a DNA microarray analysis with special attention to the genes affected by growth temperature in the mutant deficient in acidic phospholipids. Among the genes identified as highly expressed at high temperature in the pgsA null mutant, the osmB gene was shown to be dependent on the Rcs system for the high expression by dot blot hybridization. Induction of the cloned osmB in the pgsA null mutant caused the thermosensitive defect even in the absence of the Rcs system. Although the deletion of osmB did not suppress the thermosensitivity in the presence of the Rcs system, indicating a multifactorial nature of the deleterious effect of the Rcs activation, we suggest that the osmB hyperexpression is one of the causes of the Rcs-dependent lysis phenotype of the pgsA null mutant.