2025 Volume 20 Issue 1 Pages 93-100
Quorum sensing (QS) is a term referring to the language of bacteria, or intercellular communication. In recent years, the details of QS mechanisms have been rapidly elucidated in the field of marine microbiology. We investigated QS in bacteria that inhibit the growth of the paralytic shellfish toxin-producing dinoflagellate Alexandrium catenella (Group I, formerly A. tamarense) isolated from Akkeshi-ko Estuary and Akkeshi Bay. There were bacterial strains that showed strong growth inhibitory effects against A. catenella (Group I) when the colonies of bacterial cells were added to the alga. On the other hand, the same bacterial strain showed no inhibitory activity when added in liquid form (cell suspension) to A. catenella (Group I). We explored whether the growth inhibitory activity of these bacterial strains were due to QS or not using the QS inhibitor β-cyclodextrin. The algal cultures with the bacterial strains AK12 and AK24 exhibited no growth inhibition in the presence of β-cyclodextrin, showing the same results to the control without the bacterial addition. It was considered that these strains inhibited the growth of microalgae through QS using N-acyl-homoserine lactones (AHLs) as autoinducers. The strain AK12 belonged to the genus Kordia, while the strain AK24 was closely related to the genus Vibrio. This study reinforces the significance of QS as a crucial regulatory factor controlling ecosystem functions of plankton in marine environments. Considering QS will be important to elucidate the interactions between algae and bacteria in the marine environment.
