Global phylogenetic community structure and beta-diversity patterns in surface bacterioplankton metacommunities

We aimed to identify phylogenetic community patterns in abundant planktonic bacteria (Alpha-, Beta-, and Gammaproteobacteria, Actinobacteria, Cyanobacteria, and Bacteroidetes) from a worldwide range of surface waters (lakes and seas-34 sites and ca. 4500 16S rRNA gene sequences). At each site we assessed the number of observed bacterial groups and the genetic relatedness of the most abundant groups through a community phylogenetic meta-analysis approach in order to (1) explore which potential ecological processes were consistent with the observed phylogenetic patterns in community assembly and (2) disentangle the effects of space and environment in beta-diversity patterns for the different bacterial groups. Inland waters had significantly more bacterial groups and were more diverse than marine waters. Marine habitats showed a higher percentage of clustered sites than lakes, and bacterial communities were more closely related than expected by chance. Phylogenetic beta-diversity analyses revealed different patterns to both salt composition (marine vs. inland salt lakes) and salt concentration for the dominant bacteria. We observed that while beta-diversity patterns for Bacteroidetes were mostly shaped by salinity concentration, patterns in Alphaproteobacteria and Gammaproteobacteria were controlled by salt composition. Actinobacteria, Betaproteobacteria and Sphingobacteria were largely absent from marine habitats and from saline continental sites. In general and despite the lack of contextual metadata, environmental similarity was more relevant than spatial distribution for bacterial beta-diversity patterns. However, we detected a geographic signal for some inland waters' groups (i.e. Actinobacteria, Beta-, and Gammaproteobacteria). Overall, the analyses indicated differences among phylogenetic groups and reflected patterns upon which further exploration of community assembly theory could be based.