Publications

3806

SummaryLarge amounts of detrital organic matter and osmolytes accumulate in the sediments of hadal trenches (>6000 m depth) due to the funnelling effect. It is still unknown whether there are novel active microbes that depend on specific carbon sources in extreme and isolated environments. In this study, we present a novel active bacterial phylum, Candidatus Tianyabacteria in the FCB superphylum, which was enriched in sediments collected from the Challenger Deep. Genome binning resulted in high‐quality Ca. Tianyabacteria genomes representing two Ca. Tianyabacteria lineages (L1 and L2) in sediments 0–21 cm below the surface (cmbsf); L1 tends to be abundant in the upper layers (0–9 cmbsf), and L2 seems to be more prevalent in the deeper layers (12–21 cmbsf). Gene annotation and transcriptomics results indicate that the two lineages might import and catalyse amino acids and myo‐inositol into central carbon metabolism for a heterotrophic lifestyle. Probably due to differences in environmental oxygen levels, the L2 genomes harbour gene clusters responsible for denitrification and fermentation, while the L1 genomes encode octahaem cytochrome c and multicopper oxidase using unknown substrates. The Ca. Tianyabacteria are thus novel heterotrophic organisms that participate in processes of carbon, nitrogen and organic osmolyte cycling in hadal sediments.

SummaryAn anaerobic enrichment with CO from sediments of hypersaline soda lakes resulted in a methane‐forming binary culture, whereby CO was utilized by a bacterium and not the methanogenic partner. The bacterial isolate ANCO1 forms a deep‐branching phylogenetic lineage at the level of a new family within the class ‘Natranaerobiia’. It is an extreme haloalkaliphilic and moderate thermophilic acetogen utilizing CO, formate, pyruvate and lactate as electron donors and thiosulfate, nitrate (reduced to ammonia) and fumarate as electron acceptors. The genome of ANCO1 encodes a full Wood–Ljungdahl pathway allowing for CO oxidation and acetogenic conversion of pyruvate. A locus encoding Nap nitrate reductase/NrfA ammonifying nitrite reductase is also present. Thiosulfate respiration is encoded by a Phs/Psr‐like operon. The organism obviously relies on Na‐based bioenergetics, since the genome encodes for the Na+‐Rnf complex, Na+‐F1F0 ATPase and Na+‐translocating decarboxylase. Glycine betaine serves as a compatible solute. ANCO1 has an unusual membrane polar lipid composition dominated by diethers, more common among archaea, probably a result of adaptation to multiple extremophilic conditions. Overall, ANCO1 represents a unique example of a triple extremophilic CO‐oxidizing anaerobe and is classified as a novel genus and species Natranaerofaba carboxydovora in a novel family Natranaerofabacea.

Abstract Sil.va.ni.grel'la. N.L. fem. dim. n. Silvanigrella named after Silva nigra the Latin geographic name of the Schwarzwald (Black Forest) mountains located in the south‐west of Germany. Proteobacteria / Oligoflexia / Silvanigrellales / Silvanigrellaceae / Silvanigrella The genus Silvanigrella accommodates heterotrophic freshwater bacteria isolated from the water column of circumneutral or slightly acidic (pH 5–7) lakes and ponds with low ion concentrations (conductivity < 30 μS/cm). So far, only the two species Silvanigrella aquatica and Silvanigrella paludirubra have been described. Cells of the type strains have in common red pigmentation, motility, and pleomorphic morphology. In both species, the cell morphology ranges from rod‐shaped cells to filamentous forms, the cell size is variable in length and width. The type strain of S. aquatica in addition forms, densely coiled spirals. The type strains of both species grow at temperatures above 30°C, but only the type strain of S. paludirubra grows at temperatures below 10°C. Growth occurred up to supplementary NaCl concentrations of 1.0–1.1% (w/v). Both type strains utilized various organic substrates including carbohydrates, amino acids, and short‐chain fatty acids; however, the substrate spectra of the two strains differed. The most abundant fatty acid was iso‐C 15:0 for both type strains, contributing 33% to the total fatty acid content. The major respiratory quinone of S. paludirubra is menaquinone MK‐8, while the quinones of S. aquatica remained unidentified. The type strains of S. aquatica and S. paludirubra were both characterized by medium‐sized genomes (3.5 and 3.9 Mb, respectively) with low G + C content (32.6 and 29.3 mol%, respectively). DNA G + C content (mol%) : 29–33 (genome sequencing). Type species : Silvanigrella aquatica Hahn et al. 2017 VP .