Amino acid exposure modulates the bioactivity of biofilms for larval settlement of Hydroides elegans by altering bacterial community components

Possible relationships among amino acids, bacterial community structure (in terms of relative abundance of bacterial species) of marine biofilms, and larval settlement of Hydroides elegans were investigated. Two day old biofilms were first exposed to 8 different amino acids for 24 h. The bacterial abundance on the treated biofilms was then determined by epi-fluorescence microscopy, and the bacterial community profile was revealed through T-RFLP (terminal restriction fragment length polymorphism) analysis of the 16S rRNA gene. The larval settlement patterns on the treated biofilms were evaluated using laboratory bioassay. Aspartic acid and glutamic acid significantly increased bacterial abundance, modified the bacterial community structures on the biofilms, and elevated the inductive effect of the biofilms. Alanine and asparagine increased while isoleucine decreased the bioactivities of the biofilms by changing the bacterial species composition (not the bacterial abundance) of the biofilms. The other 3 amino acids (leucine, threonine, and valine) did not alter the bacterial community structures or bioactivities of the biofilms. By correlating the peaks of T-RPLP profiles with clone library results or pure bacterial strains isolated from biofilms, we partially identified the bacterial species on the biofilms that may enhance or inhibit larval settlement of H. elegans.