Abstract
Despite the important role of phages in marine systems, little is understood about how their diversity is distributed in space. Biogeographic patterns of marine phages may be difficult to detect due to their vast genetic diversity, which may not be accurately represented by conserved marker genes. To investigate the spatial biogeographic structure of marine phages, we isolated over 400 cyanophages on Synechococcus host strain WH7803 at three coastal locations in the United States (Rhode Island, Washington, and southern California). Approximately 90% of the cyanophage isolates were myoviruses, while the other 10% were podoviruses. The diversity of isolates was further characterized in two ways: (i) taxonomically, using conserved marker genes and (ii) phenotypically, by testing isolates for their ability to infect a suite of hosts, or their “host range.” Because host range is a highly variable trait even among closely related isolates, we hypothesized that host range phenotypes of cyanophage isolates would vary more strongly among locations than would taxonomic composition. Instead, we found evidence for strong biogeographic variation both in taxonomic composition and host range phenotypes, with little taxonomic overlap among the three coastal regions. For both taxonomic composition and host range phenotypes, cyanophage communities from California and Rhode Island were the most dissimilar, while Washington communities exhibited similarity to each of the other two locations. These results suggest that selection imposed by spatial variation in host dynamics influence the biogeographic distribution of cyanophages.
Highlights
Biogeography has been a cornerstone of biology for over a century, it is only within the last several decades that microorganisms have been studied in this context
The pairwise crosses between all tested cyanomyovirus isolates and the 10 host strains resulted in a binary phenotype matrix, which was converted into a similarity matrix using the Czekanowski metric (Legendre and Legendre, 1998): p sik = p yij − ykj j=1 approach, and we report the results for cyanopodoviruses as qualitative descriptions
Within CA, we found that host range phenotypes varied marginally at smaller spatial scales while the same comparison for taxonomic composition was not significant
Summary
Biogeography has been a cornerstone of biology for over a century, it is only within the last several decades that microorganisms have been studied in this context (reviewed in Martiny et al, 2006). Marine bacteriophages were thought to be widely distributed and lacking in spatial distribution patterns (Breitbart and Rohwer, 2005). Both isolation-based and direct sequencing studies have found many “ubiquitous” phage taxa that are present in samples from distant locations and diverse environments (Kellogg et al, 1995; Zhong et al, 2002; Breitbart et al, 2004; Short and Suttle, 2005; Angly et al, 2006; Goldsmith et al, 2011), or have reported phage distributions that appear unrelated to geographic distance and environmental variation (Huang et al, 2010; Jameson et al, 2011). At small spatial scales such as within a water body or coastal region, studies have found that the composition of phages infectious to cyanobacteria (cyanophages) varies little (Wang and Chen, 2004; Clasen et al, 2013)
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