Comparison of Subsurface and Surface Expression Serpentinized Fluid Microbial Communities from the Samail Ophiolite of Oman

Subsurface serpentinized fluids in the Oman Samail Ophiolite may be analogous to fluid of systems elsewhere, such as Enceladus and Europa. However, fluidic systems are dynamic and the surface likely influences the subsurface through processes such as mixing (Leong et al. 2021). A comparative study between 16S rRNA gene sequences from surface expression serpentinized fluid sediments characterized in Howells et al. (In Revision) and subsurface serpentinized fluids characterized in Rempfert et al. (2017) was conducted to identify potential biological surface influence on subsurface communities. Additionally, the observed differences between the subsurface and surface communities help identify biology that may be representative of life elsewhere. Beta diversity is significantly different between hyperalkaline surface sediment communities and hyperalkaline well communities (Bray-Curtis dissimilarity, permanova p-value = 0.001), which suggests different taxa occupy surface and well sites. Taxa of the genus, Hydrogenophaga, occur (> 1 % relative abundance) more frequently in surface fluids than in subsurface fluids (28 of 29 surface sites and 3 of 14 subsurface sites). Taxa of the genus Methanobacterium (hydrogenotrophic methanogen (Fones et al., 2021)) occur in only 3 of the 14 subsurface fluids as compared to 11 of the 29 surface sites. Taxa of the phylum, OP1, are broadly distributed in the subsurface (all except 1 fluid). At the surface, OP1 occurs at only 2 of the 29 sites. Overall, the prevalence of Hydrogenophaga (putative aerobic hydrogen oxidizers) at surface sites suggests Hydrogenophaga is an indicator of surface influence. While methanogenesis is a likely metabolism of life elsewhere, the prevalence of OP1 in the subsurface suggests the biological properties of OP1 may also be relevant to life elsewhere. OP1 sequences detected in Oman have 90 to 96% sequence identity with Candidatus Acetothermus autotrophicum, an OP1 lineage predicted to have acetogenic capabilities (Youssef et al., 2019). Fones et al. (2021) ISME, 15(4), 1121-1135 Howells et al. (In Revision) JGR Biogeosciences Leong et al. (2021) JGR Solid Earth, 126(4), e2020JB020756 Youssef et al. (2019) Environmental Microbiology Reports, 11(4), 538-547 Rempfert et al. (2017) Frontiers in Microbiology, 8(56)