Effects of dynamic succession of Vibrio biofilms on settlement of the mussel Mytilus coruscus

Vibrio, which are widely distributed in marine environments, have ability to form biofilms for the purpose of adaptation to harsh environmental conditions. Although biofilms formed by Vibrio have been known to promote larval and plantigrade settlement of the mussel Mytilus coruscus, how the dynamics succession of these biofilms during the formation impacts mussel settlement remains unknown. In this study, V. cyclitrophicus, V. chagasii and Vibrio sp. 22 with different settlement-inducing activities on plantigrades of the mussel M. coruscus were used to observe the changes of biofilm characteristics such as bacterial density, biofilm thickness and extracellular polymeric substances during the dynamic succession, and to explore subsequent effects of biofilm characteristics on mussel plantigrade settlement. The results showed that during the dynamic evolution of three Vibrio species, the bacteria on the biofilm were aggregated over time. The bacterial density and thickness of the Vibrio biofilms firstly increased with time and finally decreased. Except for Vibrio sp. 22, the bacterial density and biofilm thickness of V. cyclitrophicus and V. chagasii were correlated to the settlement of plantigrades. During the dynamic succession of Vibrio biofilms, the extracellular polysaccharides increased first with time and then began to decrease. In contrast, there was no change in the proteins and lipids on biofilms. The change trend of extracellular polysaccharide was similar to the settlement-inducing activity of biofilms, suggesting that extracellular polysaccharides play an important role in succession of biofilms regulating mussel settlement. Thus, the present finding is important to understand the interaction between biofilms and marine invertebrate settlement, and to clarify settlement mechanism of micro- and macro-organisms on artificial reefs.