AME 50:51-62 (2007)  -  DOI: https://doi.org/10.3354/ame01143

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.

KEY WORDS: Ecdysis · Cyst · Bacteria · Dinoflagellate · Bloom · Algicidal