Algicidal potential of cultivable bacteria from pelagic waters against the toxic dinoflagellate Pyrodinium bahamense (Dinophyceae)

Abstract

Associated and algicidal bacteria play roles in the succession and decline of phytoplankton blooms, including those of harmful algal bloom (HAB)-forming species. Limited studies on HAB-associated bacterial ecology have resulted in our incomplete understanding of HABs dynamics. Diverse phytoplankton-bacterial interactions have also led to studies on their potential as biocontrol tools for HABs mitigation. Here, we tested 48 cultivable pelagic bacteria from three HAB-affected areas in the Philippines (Bolinao, Sorsogon, and Matarinao) against non-axenic cultures of the toxic, thecate dinoflagellate Pyrodinium bahamense. Co-incubation with live cultures of these isolates exhibited varying levels of algicidal activities suggesting that it may not be a phylogenetically conserved property. Furthermore, majority of the isolates elicited activity against the thecate test species P. bahamense, which was not present in the area where the bacteria were isolated, implying non-specificity of action. Exposure to bacterial cells resulted in Pyrodinium pellicle cyst formation. Despite this, however, cell lysis and decline in total cell abundance were still observed, indicating strong algicidal potency of the isolates. In depth understanding of the interplay between environmental factors and algicidal bacteria-microalgal interactions may provide significant insights on the management of HABs.