Particle-association lifestyle is a phylogenetically conserved trait in bathypelagic prokaryotes

The free-living (FL) and particle-attached (PA) marine microbial communities have repeatedly been proved to differ in their diversity and composition in the photic ocean and also recently in the bathypelagic ocean at a global scale. However, although high taxonomic ranks have been proved to exhibit preferences for a PA or FL mode of life, it remains poorly understood whether two clear lifestyles do exist and how these are distributed across the prokaryotic phylogeny. We studied the FL and PA prokaryotes in 30 stations distributed worldwide within the bathypelagic oceanic realm using high throughput sequencing of their 16S rDNA. A high proportion of the bathypelagic prokaryotes were mostly found either attached to particles or freely in the surrounding water but rarely in both types of environments. In particular, this trait was deeply conserved through their phylogeny suggesting that the deep-ocean particles and the surrounding water constitute two highly distinct niches and that transi...