Microbial and Viral Roles in Hydrothermal Vent Fe Mat Elemental Cycling and Ecology at the Loihi Seamount

Iron microbial mats at hydrothermal vents mediate fluxes of Fe and other elements to the oceans. These mats are formed by Zetaproteobacteria, which are the only apparent Fe-oxidizers in the mats. They fix carbon and form Fe biominerals that form the mat architecture. The mats also host a diverse group of other organisms, including viruses, but we do not yet know how these organisms interact with Zetaproteobacteria and contribute to biogeochemical cycling. To address this, we sequenced paired metagenomes and metatranscriptomes from three samples of Fe mats at the Lo'ihi Seamount, Hawaii. These included a discrete sample of surface mat, as well as large samples that include deeper regions of the mat. Our results suggest that mat depth influences the diversity of the microbial community. Our shallow mat sample was almost entirely Zetaproteobacteria while the deeper mat samples had greater diversity, and were composed of taxa such as Zetaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, Bacteroidetes, Chloroflexi, Planctomycetes and Marinimicrobia. The Deltaproteobacteria were the second most abundant group in our deep mat sample and appeared to be very active in the nitrogen and iron cycles within the mats. Overall, the mat microbes showed significant expression of genes involved in the oxygen, nitrogen, carbon, iron and sulfur cycles. This suggests that the flanking community is contributing to the chemical cycles within the Fe mats and are possibly contributing to the success of the Zetaproteobacteria. One previously unevaluated aspect of Fe mat biogeochemistry was the potential for viral influence on the microbial groups. Our viral analysis demonstrated that almost all microbial groups within Fe mats appear to have a history of infection suggesting that viruses are an integral part of the ecosystem. We will focus on the link between the microbial groups present within the Fe mats and their inferred influence on biogeochemical cycles, highlighting the effects viruses have on the Fe mat ecosystem.