Abstract
Globally distributed and abundant cyanophages in the family Myoviridae have dsDNA genomes with variable gene content, including host-derived auxiliary metabolic genes (AMGs) that potentially can facilitate viral replication. However, it is not well understood how this variation in gene content interacts with environmental variables to shape cyanomyovirus communities. This project correlated the genetic repertoire of cyanomyoviruses with their phyologeny, and investigated cyanomyovirus ecotype distribution as a function of environmental conditions across locations and seasons. Reference cyanomyovirus genomes were compared for their overlap in gene content to infer phyologenetic distances, and these distances were compared to distances calculated based on DNA polymerase (gp43) gene sequences. In turn, gp43 partial gene sequences amplified from natural cyanophage communities were used to describe cyanomyovirus community composition and to assess the relationship between environmental variables. The results showed the following: (1) DNA polymerase gene phylogeny generally correlated with the similarity in gene content among reference cyanomyoviruses, and thus can be used to describe environmental cyanomyovirus communities; (2) spatial and seasonal patterns in cyanomyovirus communities were related to environmental variables; (3) salinity and temperature, combined with nutrient concentration were predictors of cyanomyovirus richness, diversity and community composition. This study shows that environmental variables shape viral communities by drawing on a diverse seed bank of viral genotypes. From these results it is evident that that viral ecotypes with their corresponding genetic repertoires underlie selection pressures. However, the mechanisms involved in selecting for specific viral genotypes remain to be fully understood.
Highlights
Cyanobacteria are globally distributed and abundant picophytoplankton that are estimated to account for around 25% of the world’s primary production (William, 1994; Liu et al, 1997; Field et al, 1998; Partensky et al, 1999b; Weigele et al, 2007)
To assess the similarity between phylogenetic analyses based on DNA polymerase gp43 sequences and the gene content of T4-like cyanomyoviruses, the genomes of 19 reference cyanomyoviruses were compared based on their coding sequences (CDSs) being clustered at 50% identity
This study examined differences in cyanophage community composition across a number of locations spanning a range of environmental conditions
Summary
Cyanobacteria are globally distributed and abundant picophytoplankton that are estimated to account for around 25% of the world’s primary production (William, 1994; Liu et al, 1997; Field et al, 1998; Partensky et al, 1999b; Weigele et al, 2007). Cyanophages within the family of T4-like Myoviridae, are referred to as cyanomyoviruses which are characterized by having long contractile tails and a comparably large host range that can span across genera (Suttle and Chan, 1993; Lu et al, 2001; Sullivan et al, 2003; Lindell et al, 2004) Their genome sizes range from 150 to >200 kb with variable gene content and many unknown genes. The differences in gene content and the associated adaptations to niches diversifies cyanophages into ecotypes (Marston and Martiny, 2016)
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