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Bacteria of the genus Exiguobacterium are low G + C, Gram-positive facultative anaerobes that have been repeatedly isolated from ancient Siberian permafrost. In addition, Exiguobacterium spp. have been isolated from markedly diverse sources, including Greenland glacial ice, hot springs at Yellowstone National Park, the rhizosphere of plants, and the environment of food processing plants. Strains of this hereto little known bacterium that have been retrieved from such different (and often extreme) environments are worthy of attention as they are likely to be specifically adapted to such environments and to carry variations in the genome which may correspond to psychrophilic and thermophilic adaptations. However, comparative genomic investigations of Exiguobacterium spp. from different sources have been limited. In this study, we employed different molecular approaches for the comparative analysis of 24 isolates from markedly diverse environments including ancient Siberian permafrost and hot springs at Yellowstone National Park. Pulsed-field gel electrophoresis (PFGE) with I- CeuI (an intron-encoded endonuclease), AscI and NotI were optimized for the determination of genomic fingerprints of nuclease-producing isolates. The application of a DNA macroarray for 82 putative stress-response genes yielded strain-specific hybridization profiles. Cluster analyses of 16S rRNA gene sequence data, PFGE I- CeuI restriction patterns and hybridization profiles suggested that Exiguobacterium strains formed two distinct divisions that generally agreed with temperature ranges for growth. With few exceptions (e.g., Greenland ice isolate GIC31), psychrotrophic and thermophilic isolates belonged to different divisions. [ABSTRACT FROM AUTHOR]

Previous studies in an acid-sulfate-chloride spring in Yellowstone National Park found that microbial arsenite [As(III)] oxidation is absent in regions of the spring outflow channel where H2S exceeds ~5 μM and served as a backdrop for continued efforts in the present study. Ex situ assays with microbial mat samples demonstrated immediate As(III) oxidation activity when H2S was absent or at low concentrations, suggesting the presence of As(III) oxidase enzymes that could be reactivated if H2S is removed. Cultivation experiments initiated with mat samples taken from along the H2S gradient in the outflow channel resulted in the isolation of an As (III)-oxidizing chemolithotroph from the low-H2S region of the gradient. The isolate was phylogenetically related to Acidicaldus and was characterized in vitro for spring-relevant properties, which were then compared to its distribution pattern in the spring as determined by denaturing gradient gel electrophoresis and quantitative PCR. While neither temperature nor oxygen requirements appeared to be related to the occurrence of this organism within the outflow channel, H2S concentration appeared to be an important constraint. This was verified by in vitro pure-culture modeling and kinetic experiments, which suggested that H2S inhibition of As(III) oxidation is uncompetitive in nature. In summary, the studies reported herein illustrate that H2S is a potent inhibitor of As(III) oxidation and will influence the niche opportunities and population distribution of As(III) chemolithotrophs. [ABSTRACT FROM AUTHOR]

Glycerol dialkyl glycerol tetraethers (GDGTs) are core membrane lipids originally thought to be produced mainly by (hyper)thermophilic archaea. Environmental screening of low-temperature environments showed, however, the abundant presence of structurally diverse GDGTs from both bacterial and archaeal sources. In this study, we examined the occurrences and distribution of GDGTs in hot spring environments in Yellowstone National Park with high temperatures (47 to 83°C) and mostly neutral to alkaline pHs. GDGTs with 0 to 4 cyclopentane moieties were dominant in all samples and are likely derived from both (hyper)thermophilic Crenarchaeota and Euryarchaeota. GDGTs with 4 to 8 cyclopentane moieties, likely derived from the crenarchaeotal order Sulfolobales and the euryarchaeotal order Thermoplasmatales, are usually present in much lower abundance, consistent with the relatively high pH values of the hot springs. The relative abundances of cyclopentane-containing GDGTs did not correlate with in situ temperature and pH, suggesting that other environmental and possibly genetic factors play a role as well. Crenarchaeol, a biomarker thought to be specific for nonthermophilic group I Crenarchaeota, was also found in most hot springs, though in relatively low concentrations, i.e., <5% of total GDGTs. Its abundance did not correlate with temperature, as has been reported previously. Instead, the cooccurrence of relatively abundant nonisoprenoid GDGTs thought to be derived from soil bacteria suggests a predominantly allochthonous source for crenarchaeol in these hot spring environments. Finally, the distribution of bacterial branched GDGTs suggests that they may be derived from the geothermally heated soils surrounding the hot springs. [ABSTRACT FROM AUTHOR]

Examines the rapid arsenite oxidation by Thermus aquaticus and Thermus thermophilus in Yellowstone National Park. Significance of microbes in arsenite cycling; Occurrence of arsenite oxidation as geothermal waters flow through the drainage channel; Oxidation of arsenite by antibiotic-treated cultures.