title: Viral activities and life cycles in deep subseafloor sediments.
abstract: Viruses are highly abundant in marine subsurface sediments and can even exceed the number of prokaryotes. However, their activity and quantitative impact on microbial populations are still poorly understood. Here, we use gene expression data from published continental margin subseafloor metatranscriptomes to qualitatively assess viral diversity and activity in sediments up to 159 metres below seafloor (mbsf). Mining of the metatranscriptomic data revealed 4651 representative viral homologues (RVHs), representing 2.2% of all metatranscriptome sequence reads, which have close translated homology (average 77%, range 60-97% amino acid identity) to viral proteins. Archaea-infecting RVHs are exclusively detected in the upper 30 mbsf, whereas RVHs for filamentous inoviruses predominate in the deepest sediment layers. RVHs indicative of lysogenic phage-host interactions and lytic activity, notably cell lysis, are detected at all analysed depths and suggest a dynamic virus-host association in the marine deep biosphere studied here. Ongoing lytic viral activity is further indicated by the expression of clustered, regularly interspaced, short palindromic repeat-associated cascade genes involved in cellular defence against viral attacks. The data indicate the activity of viruses in subsurface sediment of the Peruvian margin and suggest that viruses indeed cause cell mortality and may play an important role in the turnover of subseafloor microbial biomass.
authors.affiliation: Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 116, Aarhus, 8000, Denmark.
authors.forename: Tim
authors.initials: T
authors.lastname: Engelhardt
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA, 02543, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Orsi
authors.affiliation: Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 116, Aarhus, 8000, Denmark.
authors.forename: Bo Barker
authors.initials: BB
authors.lastname: Jørgensen
mesh_terms: D044822:Biodiversity; D064112:Clustered Regularly Interspaced Short Palindromic Repeats; D004279:DNA, Viral; D004783:Environmental Microbiology; D015967:Gene Expression Regulation, Viral; D019015:Geologic Sediments / Q000821:virology*; D054892:Metagenome; D056186:Metagenomics; D012367:RNA, Viral; D014780:Viruses / Q000145:classification / Q000235:genetics
chemical_list: D004279:DNA, Viral; D012367:RNA, Viral