Geothermobacter hydrogeniphilus sp. nov., a mesophilic, iron(III)-reducing bacterium from seafloor/subseafloor environments in the Pacific Ocean, and emended description of the genus Geothermobacter.

A novel mesophilic, anaerobic, mixotrophic bacterium, with designated strains EPR-MT and HR-1, was isolated from a semi-extinct hydrothermal vent at the East Pacific Rise and from an Fe-mat at Lo'ihi Seamount, respectively. The cells were Gram-negative, pleomorphic rods of about 2.0 µm in length and 0.5 µm in width. Strain EPR-MT grew between 25 and 45 °C (optimum, 37.5-40 °C), 10 and 50 g l-1 NaCl (optimum, 15-20 g l-1) and pH 5.5 and 8.6 (optimum, pH 6.4). Strain HR-1 grew between 20 and 45 °C (optimum, 37.5-40 °C), 10 and 50 g l-1 NaCl (optimum, 15-25 g l-1) and pH 5.5 and 8.6 (optimum, pH 6.4). Shortest generation times with H2 as the primary electron donor, CO2 as the carbon source and ferric citrate as terminal electron acceptor were 6.7 and 5.5 h for EPR-MT and HR-1, respectively. Fe(OH)3, MnO2, AsO4 3-, SO4 2-, SeO4 2-, S2O3 2-, S0 and NO3 - were also used as terminal electron acceptors. Acetate, yeast extract, formate, lactate, tryptone and Casamino acids also served as both electron donors and carbon sources. G+C content of the genomic DNA was 59.4 mol% for strain EPR-MT and 59.2 mol% for strain HR-1. Phylogenetic and phylogenomic analyses indicated that both strains were closely related to each other and to Geothermobacter ehrlichii, within the class δ-Proteobacteria (now within the class Desulfuromonadia). Based on phylogenetic and phylogenomic analyses in addition to physiological and biochemical characteristics, both strains were found to represent a novel species within the genus Geothermobacter, for which the name Geothermobacter hydrogeniphilus sp. nov. is proposed. Geothermobacter hydrogeniphilus is represented by type strain EPR-MT (=JCM 32109T=KCTC 15831T=ATCC TSD-173T) and strain HR-1 (=JCM 32110=KCTC 15832).

Microbial communities from Arctic marine sediments respond slowly to methane addition during ex situ enrichments.

Anaerobic methanotrophic archaea (ANME) consume methane in marine sediments, limiting its release to the water column, but their responses to changes in methane and sulfate supplies remain poorly constrained. To address how methane exposure may affect microbial communities and methane- and sulfur-cycling gene abundances in Arctic marine sediments, we collected sediments from offshore Svalbard that represent geochemical horizons where anaerobic methanotrophy is expected to be active, previously active, and long-inactive based on reaction-transport biogeochemical modelling of porewater sulfate profiles. Sediment slurries were incubated at in situ temperature and pressure with different added methane concentrations. Sediments from an active area of seepage began to reduce sulfate in a methane-dependent manner within months, preceding increased relative abundances of anaerobic methanotrophs ANME-1 within communities. In previously active and long-inactive sediments, sulfur-cycling Deltaproteobacteria became more dominant after 30 days, though these communities showed no evidence of methanotrophy after nearly 8 months of enrichment. Overall, enrichment conditions, but not methane, broadly altered microbial community structure across different enrichment times and sediment types. These results suggest that active ANME populations may require years to develop, and consequently microbial community composition may affect methanotrophic responses to potential large-scale seafloor methane releases in ways that provide insight for future modelling studies.

Metabolic versatility in a modern lineage of cyanobacteria from terrestrial hot springs.

The extent of oxygenated environments on the early Earth was much lower than today, and cyanobacteria were critical players in Earth's shift from widespread anoxia to oxygenated surface environments. Extant cyanobacteria that aggregate into cones, tufts and ridges are used to understand the long record of photosynthesis and microbe-mineral interactions during times when oxygen was much lower, i.e., the Archean and the Proterozoic. To better understand the metabolic versatility and physiological properties of these organisms, we examined publicly available genomes of cyanobacteria from modern terrestrial hydrothermal systems and a newly sequenced genome of a cyanobacterium isolated from conical and ridged microbialites that grow in occasionally sulfidic hydrothermal springs in Yellowstone National Park, USA. Phylogenomic analyses reveal that cyanobacteria from globally distributed terrestrial and shallow marine hydrothermal systems form a monophyletic clade within the Cyanobacteria phylum. Comparative genomics of this clade reveals the genetic capacity for oxygenic photosynthesis that uses photosystems I and II, and anoxygenic photosynthesis that uses a putative sulfide quinone reductase to oxidize sulfide and bypass photosystem II. Surprisingly large proportions of the newly sequenced genome from Yellowstone National Park are also dedicated to secondary metabolite production (15.1-15.6%), of which ∼6% can be attributed to antibiotic production and resistance genes. All this may be advantageous to benthic, mat-forming photosynthesizers that have to compete for light and nutrients in sporadically or permanently sulfidic environments, and may have also improved the tolerance of ancient counterparts of these cyanobacteria to sulfidic conditions in benthic communities that colonized the coastal margins in the Archean and the Proterozoic.

Genome Sequence of Geothermobacter sp. Strain EPR-M, a Deep-Sea Hydrothermal Vent Iron Reducer.

Geothermobacter sp. strain EPR-M was isolated from a hydrothermal vent on the East Pacific Rise and has been shown to participate in the reduction of Fe(III) oxides. Here, we report its 3.73-Mb draft genome sequence.