Podcast: Victoria Orphan and Elizabeth Trembath-Reichert discuss microbial life in the deep subseafloor.

Authors: Jesse McNichol, Hryhoriy Stryhanyuk, Sean P. Sylva, François Thomas, Niculina Musat, Jeffrey S. Seewald, and Stefan M. Sievert

Below the seafloor at deep-sea hot springs, mixing of geothermal fluids with seawater supports a potentially vast microbial ecosystem. Although the identity of subseafloor microorganisms is largely known, their effect on deep-ocean biogeochemical cycles cannot be predicted without quantitative measurements of their metabolic rates and growth efficiency. Here, we report on incubations of subseafloor fluids under in situ conditions that quantitatively constrain subseafloor primary productivity, biomass standing stock, and turnover time. Single-cell-based activity measurements and 16S rRNA-gene analysis showed that Campylobacteria dominated carbon fixation and that oxygen concentration and temperature drove niche partitioning of closely related phylotypes. Our data reveal a very active subseafloor biosphere that fixes carbon at a rate of up to 321 μg C⋅L⁻¹⋅d⁻¹, turns over rapidly within tens of hours, rivals the productivity of chemosynthetic symbioses above the seafloor, and significantly influences deep-ocean biogeochemical cycling.

Authors: Tiantian Yu, Weichao Wu, Wenyue Liang, Mark Alexander Lever, Kai-Uwe Hinrichs, and Fengping Wang

Members of the archaeal phylum Bathyarchaeota are among the most abundant microorganisms on Earth. Although versatile metabolic capabilities such as acetogenesis, methanogenesis, and fermentation have been suggested for bathyarchaeotal members, no direct confirmation of these metabolic functions has been achieved through growth of Bathyarchaeota in the laboratory. Here we demonstrate, on the basis of gene-copy numbers and probing of archaeal lipids, the growth of Bathyarchaeota subgroup Bathy-8 in enrichments of estuarine sediments with the biopolymer lignin. Other organic substrates (casein, oleic acid, cellulose, and phenol) did not significantly stimulate growth of Bathyarchaeota. Meanwhile, putative bathyarchaeotal tetraether lipids incorporated ¹³C from ¹³C-bicarbonate only when added in concert with lignin. Our results are consistent with organoautotrophic growth of a bathyarchaeotal group with lignin as an energy source and bicarbonate as a carbon source and shed light into the cycling of one of Earth’s most abundant biopolymers in anoxic marine sediment.

Featuring C-DEBI researcher Blair Paul.

Adaptation, a cornerstone of evolutionary change, is rarely straightforward. Acquiring a random mutation that promotes survival can take generations. Prokaryotes such as bacteria and Archaea, along with the viruses they harbor, have compact genomes, leaving them with a limited repertoire of DNA to respond to environmental change.