VIRAL IMPACTS ON MICROBIAL CARBON CYCLING AT DEEP-SEA HYDROTHERMAL VENTS

Abstract
Primary production and microbial carbon cycling controls biogeochemical cycles that influence
the habitability of our planet. Within microbial communities, abundant viruses infect cells and
release organic carbon from primary producers into dissolved and particulate carbon pools in the
ocean and fuel the microbial loop. Despite the key role of viruses in microbial carbon cycling,
linking novel viral diversity to their function remains a challenge. This challenge is especially
amplified in the undersampled dark ocean, where primary producers and their viruses are
understudied relative to microbes in the surface ocean. Here, we propose cross-institutional
research with PI Dr. Elaine Luo (University of North Carolina at Charlotte) and co-PI Dr. Gary
Trubl (Lawrence Livermore National Laboratory) to identify the key viral players and
mechanistic processes governing microbial carbon cycling in the dark ocean. The proposal
supports workforce development in postdoctoral and undergraduate training, manuscript
preparation, and presentation and networking opportunities at international conferences. Broader
impacts includes integration into scientific media products such as podcasts to share discoveries
about “viruses in the wild” and inspire public interest in deep-sea exploration and microbial
oceanography.
This project aims to identify the diversity, mechanisms, and rates of virus-induced carbon cycling
in a deep-sea hydrothermal vent system (Axial Seamount). While chemoautotrophic microbes are
known to contribute to these hotspots of primary productivity, the functional role and
biogeochemical impacts of viruses that infect them remain critical gaps in our understanding of
the dark ocean’s carbon cycle. The research aims to answer: 1) Who are the key viruses infecting
chemoautotrophic primary producers? 2) Do these viruses impact carbon cycling primarily
through lysis (bursting the host cell) or lysogeny (integrating into the host’s genome)? and 3) At
what rate does this virus-induced carbon cycling occur? Although descriptive metagenomic
studies have potential to reveal unprecedented diversity of marine microbes, linking novel
microbial diversity to their ecological function and biogeochemical impacts remains a major
challenge in the field of marine microbial ecology. Metagenomics combined with SIP can provide
critical links between metagenomic diversity and ecological function. Here, 13 C stable isotope
probing ( 13 C-SIP) is combined with metagenomics, NanoSIMS, and microscopy to reveal the
diversity, activity, mechanisms, and rate of virus-induced carbon cycling. The proposed work
combines targeted sequencing of both cellular and viral-particle samples, as well as quantitative
SIP-metagenomics, to identify virus-host interactions underpinning key microbial processes
regulating carbon cycling in the deep sea. In conjunction with NanoSIMS and microscopy, this
work aims to quantify the rate of cellular primary production and virus-induced carbon cycling
via cell lysis of primary producers – that latter of which is a key missing component of carbon
cycling in the deep sea – and advance our understanding of large-scale microbial ecosystems that
perform carbon cycling in the dark. The proposed research bridges microbial ecology with
biogeochemistry to reveal mechanistic processes driving marine carbon cycles. In the longer
term, the proposed work has broader applications to other marine ecosystems and biogeochemical
cycles and has potential to transform the way we study novel microbial diversity and processes in
the ocean.