Atribacteria from the Subseafloor Sedimentary Biosphere Disperse to the Hydrosphere through Submarine Mud Volcanoes

Abstract

Submarine mud volcanoes (SMVs) are formed by muddy sediments and breccias extruded to the seafloor from a source in the deep subseafloor and are characterized by the discharge of methane and other hydrocarbon gasses and deep-sourced fluids into the overlying seawater. Although SMVs act as a natural pipeline connecting the Earth’s surface and subsurface biospheres, the dispersal of deep-biosphere microorganisms and their ecological roles remain largely unknown. In this study, we investigated the microbial communities in sediment and overlying seawater at two SMVs located on the Ryukyu Trench off Tanegashima Island, southern Japan. The microbial communities in mud volcano sediments were generally distinct from those in the overlying seawaters and in the well-stratified Pacific margin sediments collected at the Peru Margin, the Juan de Fuca Ridge flank off Oregon, and offshore of Shimokita Peninsula, northeastern Japan. Nevertheless, in-depth analysis of different taxonomic groups at the sub-species level revealed that the taxon affiliated with Atribacteria, heterotrophic anaerobic bacteria that typically occur in organic-rich anoxic subseafloor sediments, were commonly found not only in SMV sediments but also in the overlying seawater. We designed a new oligonucleotide probe for detecting Atribacteria using the catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). CARD-FISH, digital PCR and sequencing analysis of 16S rRNA genes consistently showed that Atribacteria are abundant in the methane plumes of the two SMVs (0.58 and 1.5 × 104 cells/mL, respectively) but not in surrounding waters, suggesting that microbial cells in subseafloor sediments are dispersed as “deep-biosphere seeds” into the ocean. These findings may have important implications for the microbial transmigration between the deep subseafloor biosphere and the hydrosphere.

Comparative Study of Guaymas Basin Microbiomes: Cold Seeps vs. Hydrothermal Vents Sediments

“…Consistently, nearly similar ribotypes of ANME-2 and MBG-D lineages were detected between hydrothermal and cold seep sites (Figures 6B,C). This supports a potential continuity within these ecosystems and the possible occurrence of contemporary exchanges among neighboring seeps and vents within the Basin potentially through the hydrosphere dispersion of microorganisms, as previously suggested (Hoshino et al, 2017). However, these common lineages and ribotypes were mainly detected at the surface sediment layers of the hydrothermal sediments (0-2 cmbsf, Figure 4).…”

Gas seepage pockmark microbiomes suggest the presence of sedimentary coal seams in the Öxarfjörður graben of NE-Iceland

“…Also among abundant groups observed in the present study, the Atribacteria (group 'OP9') are often found to be predominant in methane-rich anaerobic environments such as marine sediments and subseafloor "mud volcanoes" (43,44). Although they have not been directly linked to AOM in these environments, they have been suggested to mediate AOM in some cold seep environments (10).…”

Evidence for a growth zone for deep subsurface microbial clades in near-surface anoxic sediments

“…This means that although evolutionary changes do not occur during the process of burial and near-zero cell growth over thousands of years (7), the ability to subsist over thousands of years in marine sediment is a trait that could have been selected for within the growth zone in shallow sediments. Microbes might even be ejected from deeper sediments depths by mud volcanoes into overlying seawater, where they can be carried by currents and re-deposited at the seafloor (45). Our results suggest that such organisms may revive and begin growing shortly after deposition.…”