Taxonomic, functional and biogeographic traits of the sunlit Atlantic Ocean microbiome

Microbes are major drivers of global elemental cycles in the oceans due to their high abundance and enormous taxonomic and functional diversity. Recent studies indicate that microbial communities in the oceans exhibit the greatest taxonomic richness not in the tropics, as macroorganisms with a continuous latitudinal decline, but in temperate latitudes with temperatures around 15 °C.

To further uncover the underlying diversity patterns and functional traits of marine microbial communities, we investigated gene abundances in 22 metagenomic epipelagic samples across a transect in the Southern and Atlantic Ocean between 62°S and 47°N.

The results show that the microbiome exhibits its highest functional and taxonomic richness across this transect at mid-latitudes around 15 °C. True species and KEGG orthologue diversity, however, was unchanged over the complete temperature gradient from 1 to 28°C. In contrast, the true diversity of genes was lowest at coldest temperatures and skewed to highest values around 20°C. Further, the microbial community became increasingly different over the complete temperature gradient, whereas overall community function did not show this trend, indicating a high functional redundancy in the Atlantic Ocean microbiome. Different functional gene categories, like metabolism of energy, amino acids, carbohydrates, lipids and cell motility, however, exhibited biogeographic patterns and thus reflected distinct adaptations of microbial communities to environmental and biogeochemical conditions. These findings reveal that richness and the true taxonomic and functional diversity of the sunlit Atlantic Ocean microbiome greatly diverge and reflect different evolutionary boundary conditions in and distinct adaptations to biogeographic provinces.