Bacterial induction of temporary cyst formation by the dinoflagellate Lingulodinium polyedrum

Abstract

We report the isolation of 3 novel bacterial strains from the Bacteroidetes group capable of inducing temporary cyst formation by ecdysis in the bloom-forming dinoflagellate Lingulodinium polyedrum. Phylogenetic analysis of 16S rRNA revealed that 2 of these strains are most closely related to previously identified algicidal bacteria, indicating potentially similar mechanisms of interaction. Long-term (2 wk) co-incubations of algae and bacteria under a 12:12 h light:dark cycle resulted in decreased algal cell abundances (compared to bacteria-free controls) followed by temporary cyst formation. Short-term incubations in continuous light resulted in no apparent effects of the bacteria over 2 d, but incubations in continuous darkness resulted in algal ecdysis after 24 h followed by significant decreases in total algal cell abundances after 52 h compared to controls without algicidal bacteria. We also showed that ecdysis resulted in the removal of bacteria attached to the surface of the algal cells, demonstrating a potentially direct benefit to the algae if the bacteria are harmful. We further suggest that negative interactions of bacteria on phytoplankton may be enhanced in the absence of light. © Inter-Research 2007.