Abstract
AbstractBacteria in the SAR11 clade are the most abundant members of surface marine bacterioplankton and are a critical component of global biogeochemical cycles. Similarly, pelagiphages that predate SAR11 are both ubiquitous and highly abundant in the oceans. These viruses are predicted to shape SAR11 community structures and increase carbon turnover throughout the oceans. Yet, ecological drivers of host and niche specificity of pelagiphage populations are poorly understood. Here we report the global distribution of a novel pelagiphage called Skadi isolated from the Western English Channel using a cold-water ecotype of SAR11 (HTCC1062) as bait. Skadi is closely related to the globally dominant pelagiphage HTVC010P. We show that, along with other HTVC010P-type viruses, Skadi belongs to a distinct viral family within the order Caudovirales for which we propose the name Ubiqueviridae. Metagenomic read recruitment identifies Skadi as one of the most abundant pelagiphages on Earth. Skadi is a polar specialist, replacing HTVC010P at high latitudes. Experimental evaluation of Skadi host-range against cold- and warm-water SAR11 ecotypes supported cold-water specialism. Read mapping from the Global Ocean Viromes project (GOV2) showed that relative abundance of Skadi correlated negatively with temperature, and positively with nutrients, available oxygen and chlorophyll concentrations. In contrast, relative abundance of HTVC010P correlated negatively with oxygen and positively with salinity, with no significant correlation to temperature. The majority of other pelagiphages were scarce in most marine provinces, with a few representatives constrained to discrete ecological niches. Our results suggest that pelagiphage populations persist within a global viral seed-bank, with environmental parameters and host availability selecting for a few ecotypes that dominate ocean viromes.
Publisher
Cold Spring Harbor Laboratory