Viral communities from long-term anaerobic alkane-oxidizing enrichments may promote cell surface adhesion

The anaerobic oxidation of methane and higher C2+ alkanes is a dominant metabolism within hydrocarbon-rich deep-sea sediments and is largely mediated by alkane-oxidizing archaea in metabolic partnership with syntrophic sulfate-reducing bacteria. While these processes feed a diverse ecosystem, the viral component of alkane-rich sediments has historically been overlooked. We analyzed the viral community in long-term sediment-free enrichments of alkane-degrading organisms and found that abiotic factors such as incubation temperature had a greater correlation with community composition than with the phylogenetic patterns among individual viral species. No auxiliary metabolic genes directly involved in hydrocarbon oxidation or sulfate reduction were found, but the presence of AMGs involved in heme synthesis pathways common in methane oxidizers hints at a possible viral impact on alkane degradation. We also found evidence supporting the presence of a viral genus infecting several phyla across both the bacterial and archaeal domains, including one of the sulfate-reducing bacterial partners in the alkane-oxidizing syntrophy. Lastly, we report the presence of nosD-like proteins in viruses from sediment-derived systems that are not present in water column datasets; their distribution, genomic context, and lack of canonical nosD characteristics suggest an alternate adhesion-related role in sediment communities. The number of novel viruses obtained from these enrichment cultures and their potential roles in mediating host physiology illustrate the importance of studying the viral component in laboratory and environmental systems.