Quantification of Desulfovibrio vulgaris dissimilatory sulfite reductase gene expression during electron donor- and electron acceptor-limited growth.

Harvard FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA.
Applied and Environmental Microbiology (Impact Factor: 3.95). 09/2008; 74(18):5850-3. DOI: 10.1128/AEM.00399-08
Source: PubMed

ABSTRACT Previous studies have suggested that levels of transcripts for dsrA, a gene encoding a subunit of the dissimilatory sulfite reductase, are not directly related to the rates of sulfate reduction in sediments under all conditions. This phenomenon was further investigated with chemostat-grown Desulfovibrio vulgaris. Under sulfate-limiting conditions, dsrA transcript levels increased as the bulk rates of sulfate reduction in the chemostat increased, but transcript levels were similar at all sulfate reduction rates under electron donor-limiting conditions. When both electron donor- and electron acceptor-limiting conditions were considered, there was a direct correspondence between dsrA transcript levels and the rates of sulfate reduction per cell. These results suggest that dsrA transcript levels may provide important information on the metabolic state of sulfate reducers.

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Available from: Laura Villanueva, Mar 10, 2014
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    ABSTRACT: We tested whether the gene expression of dissimilatory sulfite reductase (dsr mRNA), a critical enzyme in the sulfate reduction pathway, can serve as an indicator of the rate of sulfate reduction in natural systems. We grew Desulfovibrio vulgaris in fed-batch reactors under electron-donor limiting conditions. To simulate conditions characteristic of oligotrophic environments such as anoxic aquifers, we constrained the rates of sulfate reduction from 0.1 μM h–1 to 20 μM h–1 (0.89 – 85.9 fmol cell–1d–1) by controlling the rate of formate addition into the system. We used quantitative-PCR to measure the number of dsr mRNA transcripts per cell from biomass sampled over the course of these experiments. We observed a well-defined relationship between the rate of sulfate reduction and the number of dsr mRNA transcripts per cell. Cells from reactors maintained with the highest rate of sulfate reduction contain 315 times more dsr mRNA per cell than those in reactors with the lowest reduction rate. These results suggest we might be able to infer rates of sulfate reduction in the field by measuring the amount of dsr mRNA per cell in biomass samples. Such estimates are difficult to make directly because the rate at bacteria consume reactants and generate products cannot be observed readily in many environments, such as aquifers open to groundwater flow.
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    ABSTRACT: In the human gastrointestinal system, dietary components, including fiber, that reach the colon are fermented principally to short-chain fatty acids, hydrogen and carbon dioxide. Microbial disposal of the hydrogen generated during anaerobic fermentation in the human colon is critical to the functioning of this ecosystem. Methanogenesis by methanogenic Archaea and sulfate reduction by sulfate reducing bacteria (SRB) are the major hydrogenotrophic pathways in the human colon. Hydrogen metabolism by these microbes has an important impact on the colonic health. Methanogenic status of mammals is suggested to be under evolutionary rather than dietary control. However, information is lacking regarding the dynamics of hydrogenotrophic microbial communities among different primate species. Here I analyzed the composition of methanogens and SRB in various species of primates using PCR-DGGE fingerprinting targeting Archaea and Desulfovibrionales 16S rDNA, clone library construction of Archaea 16S rDNA and mcrA gene, and quantitative real-time PCR targeting mcrA and dsrA genes. Functionality of methanogens was determined by detection of methane from in vitro incubation of fresh feces. The results showed that the host species-specific hydrogenotrophic microbiota can be observed in some, but not all, of the captive primate species. A human colonic methanogen, Methanobrevibacter smithii, was detected in all captive hominoid species, indicating high similarity of methanogenic microbiota among these primates and humans. Comparison of wild and captive primates indicated that captive condition can be a major determinant of hydrogenotrophic microbial composition that overrides the genetic or early environmental effects, indicating the importance of proper captive management on the maintenance of colonic health.