Diversity and acyl-homoserine lactone production among subtidal biofilm-forming bacteria

Bacteria isolated from subtidal biofilms were identified via 16S rRNA gene sequencing and screened for acyl-homoserine lactone (AHL) production. In total, 68 strains were isolated from 1 to 9 d-old subtidal biofilms developed at a coastal fish farm. Identification based on partial 16S rRNA gene sequencing revealed that these isolates were distributed among 3 phylogenetic groups (4 Bacteroidetes, 13 alpha-Proteobacteria and 51 gamma- Proteobacteria), with most isolates belonging to the family Rhodobacteraceae and the genera Thalassomonas, Alteromonas, Pseudoalteromonas, Shewanella and Vibrio. AHL screening was performed using 2 AHL reporter strains, Agrobacterium tumefaciens A136 and Chromobacterium violaceum CV026. Results showed that 21 strains (31%) produced AHLs, including 3 Bacteroidetes, 5 alpha-Proteobacteria and 13 gamma-Proteobacteria. All the AHL-producing alpha-Proteobacteria belonged to the family Rhodobacteraceae, whereas the AHL-producing gamma- Proteobacteria consisted of 6 Pseudoalteromonas spp., 6 Vibrio spp. and 1 Thalassomonas sp. This is the first report of AHL-producing marine bacteria in the genera Flammeovirga, Pseudoalteromonas and Thalassomonas. The family Rhodobacteraceae (11 isolates) and the genera Vibrio (15 isolates) and Pseudoalteromonas (17 isolates) had the greatest number of AHL-producing isolates. AHL profiling of the AHL- producing isolates was performed by GC-MS. Most AHL-producing isolates produced several different AHLs, many of which were long-chain- and 3-oxo- AHLs. The widespread occurrence of AHL-producing bacteria in subtidal biofilms suggests that AHLs may play a role in the community development in this environment.