Microbial diversity of sinking particulate organic matter in subtropical oceans

Abstract

The bacterial diversity on sinking particulate organic matter (POM) from open ocean environments was characterized using gene-based sequencing techniques. The phylogenetic diversity of bacteria associated with sinking aggregates was investigated by sequencing of the bacterial 16S rRNA gene using Sanger and high-throughput sequencing technologies. Sinking POM was collected by free-floating sediment trap arrays from multiple sites in the North and South Pacific Oceans. Sinking POM was processed for multiple measurements to assess the quality of the POM and the diversity of its associated microbial consortia. The project in the North Pacific Subtropical Gyre (NPSG) focused on characterizations of aggregate-associated bacterial diversity during the summertime. Although sea surface chlorophyll a concentrations were not significantly different across the six study sites, we observed distinct differences in the bacterial diversity associated with sinking POM from these regions. Diversity was most similar among samples collected on the same expedition. The project in the South Pacific Ocean focused on comparisons of aggregate-associated microbial diversity from sites with distinctively different productivity and export flux regimes. Sinking POM was collected from three stations spanning more than 3000 km across the Eastern Tropical South Pacific (ETSP). Our results suggest that aggregate-associated diversity is not directly correlated to the quality of sinking POM. Additionally, there was no apparent pattern between microbial diversity and other parameters, including the depth at which the sample was collected, the ambient dissolved oxygen concentration, or the total photosynthetic biomass flux.