Redefinition of archetypal phytoplankton-associated bacteria taxa based on globally distributed dinoflagellates and diatoms

Bacteria colonizing in the phycosphere formed by phytoplankton exudates play important roles in marine ecosystems, yet their taxonomy is poorly defined. Here, we customized the analytical approaches for the microalga-attached microbiotas from 110 diatom and 86 dinoflagellate samples to reveal key bacterial players and their ecological significance in the phycosphere. The results demonstrated a co-occurrence of host-specificity and conservation of phytoplankton-associated bacterial communities, defined 8 diatom- and 23 dinoflagellate-affiliated characteristic genera, as well as identifying 14 core genera prevalent with phytoplankton populations. Further classification of these 14 core genera into three tiers showed their distinct ecological features regarding occupancy, connectivity and community-stabilizing, whilst also matching their inherent metabolic properties. Our study redefines the archetypal phytoplankton-associated bacteria taxa more specifically up to the genus level, highlighting the significance of rarely noticed bacteria in the phycosphere, which is invaluable when selecting target bacteria for studying phytoplankton-bacteria interactions.