Abstract
The exploration of bacterial diversity in the global ocean has revealed new taxa and previously unrecognized metabolic potential; however, our understanding of what regulates this diversity is limited. Using terminal restriction fragment length polymorphism (T-RFLP) data from bacterial small-subunit ribosomal RNA genes we show that, independent of depth and time, a large fraction of bacterioplankton co-occurrence patterns are non-random in the oligotrophic North Pacific subtropical gyre (NPSG). Pair-wise correlations of all identified operational taxonomic units (OTUs) revealed a high degree of significance, with 6.6% of the pair-wise co-occurrences being negatively correlated and 20.7% of them being positive. The most abundant OTUs, putatively identified as Prochlorococcus, SAR11, and SAR116 bacteria, were among the most correlated OTUs. As expected, bacterial community composition lacked statistically significant patterns of seasonality in the mostly stratified water column except in a few depth horizons of the sunlit surface waters, with higher frequency variations in community structure apparently related to populations associated with the deep chlorophyll maximum. Communities were structured vertically into epipelagic, mesopelagic, and bathypelagic populations. Permutation-based statistical analyses of T-RFLP data and their corresponding metadata revealed a broad range of putative environmental drivers controlling bacterioplankton community composition in the NPSG, including concentrations of inorganic nutrients and phytoplankton pigments. Together, our results suggest that deterministic forces such as environmental filtering and interactions among taxa determine bacterioplankton community patterns, and consequently affect ecosystem functions in the NPSG.
Highlights
The bulk of the world’s ocean is oligotrophic and, in terms of both biomass and ecosystem function, is dominated by microorganisms (Cho and Azam, 1988)
Our results suggest that deterministic forces such as environmental filtering and interactions among taxa determine bacterioplankton community patterns, and affect ecosystem functions in the North Pacific subtropical gyre (NPSG)
We aimed to explore patterns in bacterioplankton community structure within water samples collected from various depths over a 3-year period at Station ALOHA in the North Pacific subtropical gyre (NPSG), the world’s largest oligotrophic marine ecosystem (Karl, 1999)
Summary
The bulk of the world’s ocean is oligotrophic and, in terms of both biomass and ecosystem function, is dominated by microorganisms (Cho and Azam, 1988). Despite increasing efforts to understand emergent patterns in the abundances and distributions of microbial taxa in seawater (e.g., Morris et al, 2002; Fuhrman et al, 2006; Johnson et al, 2006; Carlson et al, 2009; Eiler et al, 2009), the mechanisms that determine patterns observed in entire microbial communities remain largely unknown (Fuhrman and Steele, 2008; Steele et al, 2011) This stands in contrast to macroorganismal ecology, where the ecological mechanisms that underlie and maintain community patterns (beta-diversity) and (alpha-) diversity (often termed “assembly rules”) have been a central theme (e.g., Keddy and Weiher, 2001). Patterns in alpha- and beta-diversity of macroorganisms have been suggested to be the result of the interplay between regional and local processes: regional processes include dispersal, historical legacies, speciation, extinction, and geographic and climatic conditions, whereas local processes include interactions among organisms, and between organisms and their local environment
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