[Roles of microbes in matter cycles in phycosphere niche.]

Phytoplankton is the main driver of marine primary production and matter cycles. Their ecological functions have closely linked to the associated microbes. Although microbial biodiversity is high in all kinds of algal hosts (such as dinoflagellate, diatoms and blue-green algae), some he-terotrophic bacteria (Alphaproteobacteria, Gammaproteobacteria, Flavobacteria, and Actinobacteria) often appear as the dominant communities. In algae-bacteria symbiosis, microbes play important ecological roles, such as regulating microbial food web, mediating the energy flow & nutrient cycling, and maintaining the balance of ecological system. In this review, we summarized the bacterial functions in phycosphere environment, and discussed their contribution to biogeochemical cycle and co-evolution. Particularly, we attempted to take Flavobacteria and Roseobacters as the examples to reveal the metabolic behavior and survive strategies, for better understanding the ecological cha-racterization and co-evolution of "resident species" in phycosphere niche.