Effects Of Vibrio Biofilm And Dynamic Succession On The Settlement Of The Mussel Mytilus Coruscus

Vibrio is a common Gram-negative bacterium and is widely isolated from marine environment.Most bacteria adapt environmental changes by form biofilms(BFs).Mytilus coruscus,a kind of important shellfish,needs to get through the process of settlement and metamorphosis from the swimming larvae state to the settlement live state,from larva to plantigrades.And plantigrades has the ability to second settlement,when the environment changes,the plantigrades will find new suitable settlements to reattach.Previous studies proved that Vibrio(BFs)is inductive for larval settlement and metamorphosis in mussel M.coruscus.Whether different species of Vibrio are inductive and what are the factors that influence the inducing activity are still unknown.Moreover,the formation process of BFs is a dynamic succession process.Bacteria settle on suitable substrate and then secrete extracellular products to form a three-dimensional structure.During the BFs formation,characters such us bacterial density,thickness and extracellular products changed over time.The effects of different Vibrio sp.on larval settlement and metamorphosis and the effects of dynamic succession process on plantigrades of BFs were examined as well in this study.The details are as follows:1.The effect of Vibrio BFs on larval settlement and metamorphosis of the mussel M.coruscusEight different Vibrio sp.were isolated to form BFs under different initial concentrations and its effect on settlement and metamorphosis of larvae of the mussel M.coruscus were examined.To explore the influence factors of inducing activity of Vibrio sp.BFs,the highly inductive Vibrio sp.22 BFs were treated by formalin,organic solvent and temperature,and the water-soluble products of BFs were collected to examine its inducing activity.The results showed that all tested Vibrio sp.showed inducing activity compared with the blank group(p<0.05).Of which,Vibrio sp.22 had the highest inducing activity of 40%±2%when the bacterial density was 5.4±0.08×10~8 cells/ml,and the inducing other six Vibrio sp.juveniles ranged from 11%to 25%.In addition to Vibrio sp23,the bacterial density of 8 Vibrio BFs was correlated with the settlement and metamorphosis rate of the mussels M.coruscus.The bacterial density of Vibrio sp.5and Vibrio sp.22 was positively correlated with the inducing activity,the rest of five Vibrio sp.negatively correlated the inducing activity.The settlement bioassay of treated BFs indicated that the water-soluble cues and surface-bound cues play synergetic roles in larval settlement and metamorphosis.2.Effects of dynamic succession of Vibrio biofilm on settlement of plantigrades of the mussel M.coruscus.Monospecific bacterial biofilm formation is a process of dynamic succession.Three strains of Vibrio cyclitrophicus,Vibrio chagasii and Vibrio sp.22 with different inducing activities were selected to investigate the changes of biological characteristics such as bacterial density,membrane thickness and extracellular products during BFs formation of three Vibrio sp.and to explore its effect on settlement of plantigrades of the M.coruscus.The results showed that during the process of BFs formation of three Vibrio species,bacterial density,thickness and exopolysaccharides of BFs increased to peak value and then decreased over time.The BFs of V.cyclitrophicus and V.chagasii showed correlation between their inducing activity and the bacterial density and thickness.The distribution of exopolysaccharides and the inducing activity of BFs showed same tendency over time,so it was speculated that the exopolysaccharides might be one of the influence factors of inducing activity.In this experiment,the effects of different Vibrio BFs on the settlement and metamorphosis of larvae of the mussel M.coruscus were studied.The results showed that 8 different Vibrio BFs all showed inducing activity.The correlation analysis showed that the bacterial density was one of the factors which affect the induction activity.The extracellular product distribution which was observed by fluorescence staining of BFs might affect inducing activity of BFs and the difference of inducing activity might due to the difference of conditioned water(CW).The water-soluble cues and surface-bound cues played synergetic roles in inducing larval settlement and metamorphosis.The effect of dynamic succession of Vibrio biofilm on the settlement of the mussel M.coruscus was also studied.The changes of bacterial density,thickness and distribution of extracellular products of BFs during dynamic succession process affected the plantigrades of the mussel M.coruscus settlement.The BFs of same Vibrio strain showed different inducing activities of larvae and plantigrades and the result indicated that two settlement processes are regulated by different mechanisms.This study establishes foundation for researching the mechanism of settlement of mussel M.coruscus in future,and also provides a theoretical basis for regulating the settlement of the mussel M.coruscus by BFs.