Effects of bacterial biofilms on settlement of plantigrades of the mussel Mytilus coruscus

• We investigated the effects of bacterial biofilms on settlement of plantigrades.
• All tested bacterial biofilms enhanced the settlement of plantigrades.
• The inducing activity was not correlated with phylogenetic relationship and source.
• A viable bacterial biofilm was required for plantigrade settlement.
• The chemical cues in bacteria were susceptible to ethanol and heat treatment.

This study investigated in the laboratory the effects on settlement of Mytilus coruscus plantigrades of bacteria isolated from the biofilms grown on natural and abiotic surfaces. Plantigrades settled in response to all bacterial biofilms tested. The inducing activity of individual bacterial isolates was not correlated with their phylogenetic relationship nor with surfaces isolated. Among 10 bacterial species, bacterial density was significantly correlated with the inducing activity for each strain except for Pseudoalteromonas sp. 2. Furthermore, Shewanella sp. 1 biofilms and Pseudoalteromonas sp. 4 biofilms responsible for inducing settlement of plantigrades were subjected to different treatments to investigate the characteristics of the cues in these two species of bacteria. Treatments of Shewanella sp. 1 biofilms and Pseudoalteromonas sp. 4 biofilms with formalin, antibiotics, ultraviolet irradiation, heat and ethanol resulted in a significant decrease or loss of their inducing activities. Cell survival within treated biofilms also decreased significantly. The chemical cues produced by Shewanella sp. 1 biofilms and Pseudoalteromonas sp. 4 biofilms were susceptible to ethanol and heat treatment. Thus, the above bacterial biofilms were shown to be effective inducers of plantigrade settlement, and may be used to enhance settlement of plantigrades for the Chinese aquaculture industry.