Pacific Ocean Microbiome

Biogeographic patterns, known for plants and animals, have been found more recently for microorganisms as well, mainly due to the advancements in high throughput sequencing of phylogenetic marker genes and metagenomic shotgun analyses. Despite accumulating data on microbial biogeographic patterns in terrestrial and aquatic environments, we still lack a comprehensive understanding of how these patterns establish, in particular in ocean basins. Here we show the relative significance of the ecological mechanisms selection, dispersal and drift for shaping the composition of microbial communities in the Pacific Ocean over a transect of 12400 km between subantarctic and subarctic regions. In the epipelagic, homogeneous selection contributes 50-60% and drift least to the three mechanism for the assembly of prokaryotic communities whereas in the upper mesopelagic, drift is the relatively most important mechanism for the particle-associated subcommunities. For eukaryotes >8 µm, drift is the predominant mechanism but homogeneous selection also important in the epipelagic. As species interactions are essential for structuring microbial communities we further analysed co-occurrence based community metrics to assess biogeographic patterns over the transect. These features explained much better variations in microbial community composition as a function of abiotic and biotic variables than geographic or phylogenetic distance measures. Our analyses are important to better understand assembly processes of microbial communities in the biogeochemically most active layers of the largest ocean. Similar principles presumably act upon microbial community assembly in other ocean basins.