Quorum sensing in marine snow and its possible influence on production of extracellular hydrolytic enzymes in marine snow bacterium Pantoea ananatis B9

Marine snow is a continuous shower of organic and inorganic detritus, and plays a crucial role in transporting materials from the sea surface to the deep ocean. The aims of the current study were to identify N-acyl homoserine lactone (AHL)-based quorum sensing (QS) signaling molecules directly from marine snow particles and to investigate the possible regulatory link between QS signals and extracellular hydrolytic enzymes produced by marine snow bacteria. The marine snow samples were collected from the surface water of China marginal seas. Two AHLs, i.e. 3OC6-HSL and C8-HSL, were identified directly from marine snow particles, while six different AHL signals, i.e. C4-HSL, 3OC6-HSL, C6-HSL, C10-HSL, C12-HSL and C14-HSL were produced by Pantoea ananatis B9 inhabiting natural marine snow particles. Of the extracellular hydrolytic enzymes produced by P. ananatis B9, alkaline phosphatase activity was highly enhanced in growth medium supplemented with exogenous AHL (C10-HSL), while quorum quenching enzyme (AiiA) drastically reduced the enzyme activity. To our knowledge, this is the first report revealing six different AHL signals produced by P. ananatis B9 and AHL-based QS system enhanced the extracellular hydrolytic enzyme in P. ananatis B9. Furthermore, this study first time revealing 3OC6-HSL production by Paracoccus carotinifaciens affiliated with Alphaproteobacteria.