Potential for biogeochemical cycling of sulfur, iron and carbon within massive sulfide deposits below the seafloor

Abstract

Seafloor massive sulfides are a potential energy source for the support of chemosynthetic ecosystems in dark, deep-sea environments; however, little is known about microbial communities in these ecosystems, especially below the seafloor. In the present study, we performed culture-independent molecular analyses of sub-seafloor sulfide samples collected in the Southern Mariana Trough by drilling. The depth for the samples ranged from 0.52 m to 2.67 m below the seafloor. A combination of 16S rRNA and functional gene analyses suggested the presence of chemoautotrophs, sulfur-oxidizers, sulfate-reducers, iron-oxidizers and iron-reducers. In addition, mineralogical and thermodynamic analyses are consistent with chemosynthetic microbial communities sustained by sulfide minerals below the seafloor. Although distinct bacterial community compositions were found among the sub-seafloor sulfide samples and hydrothermally inactive sulfide chimneys on the seafloor collected from various areas, we also found common bacterial members at species level including the sulfur-oxidizers and sulfate-reducers, suggesting that the common members are widely distributed within massive sulfide deposits on and below the seafloor and play a key role in the ecosystem function.

Coexistence of Fe(II)- and Mn(II)-oxidizing bacteria govern the formation of deep sea umber deposits

“…Clones TVG5-B4 and TVG5-B9 are 99% similar to clones recovered from Loihi hydrothermal vent and Southern Mariana Trough deposits (Moyer et al, 1995;Kato et al, 2015). Clone TVG5-B76 is 96% similar to the clone from submarine hydrothermal systems (Forget et al, 2010).…”

Genomic Description of ‘Candidatus Abyssubacteria,’ a Novel Subsurface Lineage Within the Candidate Phylum Hydrogenedentes

“…Abyssubacteria’, are globally distributed ( Figure 4 ) in marine and terrestrial, shallow and deep, subsurface environments ( Supplementary Data File 4 ). Interestingly, BLAST results >90% identical to SURF_17 (the generally accepted cutoff for family level lineage) are all from deep subsurface environments, including freshwater aquifers (Flynn et al, 2013), gas hydrates, deep-sea hydrothermal sediments and deep-sea sediments from the Mariana Trough (Kato et al, 2015). Indeed, the only 16S rRNA gene sequence >98% identical to that for SURF_17, the accepted cutoff for same species lineage (Yarza et al, 2014), was collected from the world’s deepest sinkhole in Zacatón, Mexico (Sahl et al, 2010).…”

What Do We Really Know about the Role of Microorganisms in Iron Sulfide Mineral Formation?

“…In sediments contaminated by mine tailing drainage, microbial cell surfaces were associated with FeS and NiS (Ferris et al, 1987). In hydrothermal vents, which result in the formation of submarine ores, both metabolically active SRP and dissimilatory sulfite reductase (dsr) genes have been found in the outer walls of chimneys and in seafloor massive sulfide deposits, where seawater sulfate is entrained (Nakagawa et al, 2004;Kormas et al, 2006;Frank et al, 2013;Kato et al, 2015). Nonetheless, the role of microorganisms in sulfide mineral formation at vents is considered quantitatively unimportant, due to the abundant abiotic sulfide provided by the vents.…”