Community structure and functional determinants of free-living and particle associated bacterioplankton and mycoplankton in sub-Antarctic islands

AbstractIn Southern Ocean islands such as the Prince Edward Islands (PEIs), the interactions between landmasses, the surrounding waters and macrofauna result in complex trophic interactions underpinned by microbial communities. However, we lack a mechanistic understanding regarding particle attached (PA) and free living (FL) microbiota as drivers of functional processes. To reduce this knowledge deficit, we assessed the community structure and composition of PA and FL microbiota in the PEIs. Fluorescence maximum (Fmax), oxygen minimum zone (OMZ) and bathypelagic zone (Deep) samples were collected from 10 locations. Physicochemical factors were used to test the effects of the environment on PEI microbiota. Phylogenetic analysis of 16S rRNA gene and ITS sequences of 18S and 23S rRNA genes revealed distinct shifts in bacterioplankton and fungal communities, respectively. Differences in PA and FL microbiomes also coincided with differences in depth, oceanographic features and physicochemical variables. Extracellular enzymatic activities specific for carbon, nitrogen and phosphorus acquisition were not congruent with community composition but were closely linked to substrate availability and depth. These results suggest that microbial extracellular enzymatic activities were driven primarily by nutrient availability. Together, these data provide important insights regarding the complex interplay between biotic and abiotic drivers as drivers of near-shore PA and FL microbial communities in the SO.