Project description:Desulfotomaculum nigrificans and D. carboxydivorans are moderately thermophilic members of the polyphyletic spore-forming genus Desulfotomaculum in the family Peptococcaceae. They are phylogenetically very closely related and belong to 'subgroup a' of the Desulfotomaculum cluster 1. D. nigrificans and D. carboxydivorans have a similar growth substrate spectrum; they can grow with glucose and fructose as electron donors in the presence of sulfate. Additionally, both species are able to ferment fructose, although fermentation of glucose is only reported for D. carboxydivorans. D. nigrificans is able to grow with 20% carbon monoxide (CO) coupled to sulfate reduction, while D. carboxydivorans can grow at 100% CO with and without sulfate. Hydrogen is produced during growth with CO by D. carboxydivorans. Here we present a summary of the features of D. nigrificans and D. carboxydivorans together with the description of the complete genome sequencing and annotation of both strains. Moreover, we compared the genomes of both strains to reveal their differences. This comparison led us to propose a reclassification of D. carboxydivorans as a later heterotypic synonym of D. nigrificans.
Project description:Desulfotomaculum reducens is the first Gram-positive sulfate- and metal- reducing bacterium for which the transcriptomic response to uranium exposure has been evaluated. The genes upregulated during fermentative growth in the presence of U(VI) as compared to its absence included those encoding for proteins involved in respiration such as NADH quinone oxidoreductase and heterodisulfide reductase. This finding suggested that electrons were shuttled to the electron transport chain during fermentation which points to the reduction of U(VI) as a metabolic process. While U(IV) is typically insoluble and readily removable by filtration, U(IV) produced during active growth was not retained by a 0.2 µm pore size filter and filtration was not sufficient to differentiate between U(VI) and U(IV). In addition, genes involved in iron homeostasis were upregulated in the presence of uranium, which was consistent with the upregulation of genes involved in c-type cytochrome biogenesis. Despite the upregulation of cytochrome biosynthesis genes, the sole c-type cytochrome encoded in the genome was not differentially expressed. Finally, genes encoding metal efflux pumps were also upregulated indicating the toxic nature of uranium. Analysis of the time-dependent gene expression showed that sporulation was the dominant process at the early stationary phase and that the presence of U at that stage did not impact expression.
Project description:Comparative Proteomic Analysis of Desulfotomaculum reducens MI-1: Insights into the Metabolic Versatility of a Gram-positive Sulfate and Metal-reducing Bacterium
Project description:The aim of this study was to unravel the methanol metabolism of Desulfotomaculum kuznetsovii. Anaerobic methylotrophs, such as methanogens and acetogens, use a pathway initiated by a cobalamine-containing methanol methyltransferase, whereas aerobic methylotrophs generally oxidize methanol to formaldehyde through a pathway initiated by a methanol dehydrogenase. Sulfate-respiring cells grown with methanol in the presence and absence of cobalt and vitamin B12 were analyzed and compared with cells grown with lactate or ethanol. Proteome analysis showed the presence of two methanol degrading pathways in D. kuznetsovii: a cobalt-dependent methanol methyltransferase and a cobalt-independent alcohol dehydrogenase. This is the first time that two methanol pathways have been shown to be present in a single microorganism, and we hypothesize this can give D. kuznetsovii a competitive advantage.
