Draft Genome Sequence of the Moderately Thermophilic Bacterium Schleiferia thermophila Strain Yellowstone (Bacteroidetes)

Leptospira interrogans encodes a canonical BamA and three novel noNterm Omp85 outer membrane protein paralogs

The Omp85 family of outer membrane proteins are ubiquitously distributed among diderm bacteria and play essential roles in outer membrane (OM) biogenesis. The majority of Omp85 orthologs are bipartite and consist of a conserved OM-embedded 16-stranded beta-barrel and variable periplasmic functional domains. Here, we demonstrate that Leptospira interrogans encodes four distinct Omp85 proteins. The presumptive leptospiral BamA, LIC11623, contains a noncanonical POTRA4 periplasmic domain that is conserved across Leptospiraceae. The remaining three leptospiral Omp85 proteins, LIC12252, LIC12254 and LIC12258, contain conserved beta-barrels but lack periplasmic domains. Two of the three 'noNterm' Omp85-like proteins were upregulated by leptospires in urine from infected mice compared to in vitro and/or following cultivation within rat peritoneal cavities. Mice infected with a L. interrogans lic11254 transposon mutant shed tenfold fewer leptospires in their urine compared to mice infected with the wild-type parent. Analyses of pathogenic and saprophytic Leptospira spp. identified five groups of noNterm Omp85 paralogs, including one pathogen- and two saprophyte-specific groups. Expanding our analysis beyond Leptospira spp., we identified additional noNterm Omp85 orthologs in bacteria isolated from diverse environments, suggesting a potential role for these previously unrecognized noNterm Omp85 proteins in physiological adaptation to harsh conditions.

"Candidatus Thermonerobacter thiotrophicus," A Non-phototrophic Member of the Bacteroidetes/Chlorobi With Dissimilatory Sulfur Metabolism in Hot Spring Mat Communities

In this study we present evidence for a novel, thermophilic bacterium with dissimilatory sulfur metabolism, tentatively named “Candidatus Thermonerobacter thiotrophicus,” which is affiliated with the Bacteroides/Ignavibacteria/Chlorobi and which we predict to be a sulfate reducer. Dissimilatory sulfate reduction (DSR) is an important and ancient metabolic process for energy conservation with global importance for geochemical sulfur and carbon cycling. Characterized sulfate-reducing microorganisms (SRM) are found in a limited number of bacterial and archaeal phyla. However, based on highly diverse environmental dsrAB sequences, a variety of uncultivated and unidentified SRM must exist. The recent development of high-throughput sequencing methods allows the phylogenetic identification of some of these uncultured SRM. In this study, we identified a novel putative SRM inhabiting hot spring microbial mats that is a member of the OPB56 clade (“Ca. Kapabacteria”) within the Bacteroidetes/Chlorobi superphylum. Partial genomes for this new organism were retrieved from metagenomes from three different hot springs in Yellowstone National Park, United States, and Japan. Supporting the prediction of a sulfate-reducing metabolism for this organism during period of anoxia, diel metatranscriptomic analyses indicate highest relative transcript levels in situ for all DSR-related genes at night. The presence of terminal oxidases, which are transcribed during the day, further suggests that these organisms might also perform aerobic respiration. The relative phylogenetic proximity to the sulfur-oxidizing, chlorophototrophic Chlorobi further raises new questions about the evolution of dissimilatory sulfur metabolism.

Effect of light wavelength on hot spring microbial mat biodiversity

Hot spring associated phototrophic microbial mats are purely microbial communities, in which phototrophic bacteria function as primary producers and thus shape the community. The microbial mats at Nakabusa hot springs in Japan harbor diverse photosynthetic bacteria, mainly Thermosynechococcus, Chloroflexus, and Roseiflexus, which use light of different wavelength for energy conversion. The aim of this study was to investigate the effect of the phototrophs on biodiversity and community composition in hot spring microbial mats. For this, we specifically activated the different phototrophs by irradiating the mats with different wavelengths in situ. We used 625, 730, and 890 nm wavelength LEDs alone or in combination and confirmed the hypothesized increase in relative abundance of different phototrophs by 16S rRNA gene sequencing. In addition to the increase of the targeted phototrophs, we studied the effect of the different treatments on chemotrophic members. The specific activation of Thermosynechococcus led to increased abundance of several other bacteria, whereas wavelengths specific to Chloroflexus and Roseiflexus induced a decrease in >50% of the community members as compared to the dark conditions. This suggests that the growth of Thermosynechococcus at the surface layer benefits many community members, whereas less benefit is obtained from an increase in filamentous anoxygenic phototrophs Chloroflexus and Roseiflexus. The increases in relative abundance of chemotrophs under different light conditions suggest a relationship between the two groups. Aerobic chemoheterotrophs such as Thermus sp. and Meiothermus sp. are thought to benefit from aerobic conditions and organic carbon in the form of photosynthates by Thermosynechococcus, while the oxidation of sulfide and production of elemental sulfur by filamentous anoxygenic phototrophs benefit the sulfur-disproportionating Caldimicrobium thiodismutans. In this study, we used an experimental approach under controlled environmental conditions for the analysis of natural microbial communities, which proved to be a powerful tool to study interspecies relationships in the microbiome.

The Dark Side of the Mushroom Spring Microbial Mat: Life in the Shadow of Chlorophototrophs. I. Microbial Diversity Based on 16S rRNA Gene Amplicons and Metagenomic Sequencing

Microbial-mat communities in the effluent channels of Octopus and Mushroom Springs within the Lower Geyser Basin at Yellowstone National Park have been studied for nearly 50 years. The emphasis has mostly focused on the chlorophototrophic bacterial organisms of the phyla Cyanobacteria and Chloroflexi. In contrast, the diversity and metabolic functions of the heterotrophic community in the microoxic/anoxic region of the mat are not well understood. In this study we analyzed the orange-colored undermat of the microbial community of Mushroom Spring using metagenomic and rRNA-amplicon (iTag) analyses. Our analyses disclosed a highly diverse community exhibiting a high degree of unevenness, strongly dominated by a single taxon, the filamentous anoxygenic phototroph, Roseiflexus spp. The second most abundant organisms belonged to the Thermotogae, which have been hypothesized to be a major source of H2 from fermentation that could enable photomixotrophic metabolism by Chloroflexus and Roseiflexus spp. Other abundant organisms include two members of the Armatimonadetes (OP10); Thermocrinis sp.; and phototrophic and heterotrophic members of the Chloroflexi. Further, an Atribacteria (OP9/JS1) member; a sulfate-reducing Thermodesulfovibrio sp.; a Planctomycetes member; a member of the EM3 group tentatively affiliated with the Thermotogae, as well as a putative member of the Arminicenantes (OP8) represented ≥1% of the reads. Archaea were not abundant in the iTag analysis, and no metagenomic bin representing an archaeon was identified. A high microdiversity of 16S rRNA gene sequences was identified for the dominant taxon, Roseiflexus spp. Previous studies demonstrated that highly similar Synechococcus variants in the upper layer of the mats represent ecological species populations with specific ecological adaptations. This study suggests that similar putative ecotypes specifically adapted to different niches occur within the undermat community, particularly for Roseiflexus spp.

Refining the phylum Chlorobi by resolving the phylogeny and metabolic potential of the representative of a deeply branching, uncultivated lineage

Recent studies have expanded the phylum Chlorobi, demonstrating that the green sulfur bacteria (GSB), the original cultured representatives of the phylum, are a part of a broader lineage whose members have more diverse metabolic capabilities that overlap with members of the phylum Bacteroidetes. The 16S rRNA gene of an uncultivated clone, OPB56, distantly related to the phyla Chlorobi and Bacteroidetes, was recovered from Obsidian Pool in Yellowstone National Park; however, the detailed phylogeny and function of OPB56 and related clones have remained unknown. Culturing of thermophilic bacterial consortia from compost by adaptation to grow on ionic-liquid pretreated switchgrass provided a consortium in which one of the most abundant members, NICIL-2, clustered with OPB56-related clones. Phylogenetic analysis using the full-length 16S rRNA gene from NICIL-2 demonstrated that it was part of a monophyletic clade, referred to as OPB56, distinct from the Bacteroidetes and Chlorobi. A near complete draft genome (>95% complete) was recovered from metagenomic data from the culture adapted to grow on ionic-liquid pretreated switchgrass using an automated binning algorithm, and this genome was used for marker gene-based phylogenetic analysis and metabolic reconstruction. Six additional genomes related to NICIL-2 were reconstructed from metagenomic data sets obtained from thermal springs at Yellowstone National Park and Nevada Great Boiling Spring. In contrast to the 16S rRNA gene phylogenetic analysis, protein phylogenetic analysis was most consistent with the clustering of the Chlorobea, Ignavibacteria and OPB56 into a single phylum level clade. Metabolic reconstruction of NICIL-2 demonstrated a close linkage with the class Ignavibacteria and the family Rhodothermaceae, a deeply branching Bacteroidetes lineage. The combined phylogenetic and functional analysis of the NICIL-2 genome has refined the membership in the phylum Chlorobi and emphasized the close evolutionary and metabolic relationship between the phyla Chlorobi and the Bacteroidetes.