Microbial community coexisting with harmful alga Karenia mikimotoi and microbial control of algal bloom in laboratory

Algicidal bacteria have been frequently isolated from algal blooming areas. However, knowledge regarding the microbial communities coexisting with microalgae and their potential application in preventing harmful algal blooms (HABs) is limited. In this study, we investigated the composition of the microbial community coexisting with harmful alga Karenia mikimotoi and its responses to algal control via nutrient stimulation or by adding algicidal strain in microcosms. The microorganisms inhabiting the K. mikimotoi culture consisted of 24 identified phyla, including dominant Proteobacteria (relative abundance 76.24%±7.28%) and Bacteroidetes (22.67%±8.32%). Rhodobacteraceae, Phaeodactylibacter , and Maritimibacter predominated during the algal cultivation. Both the added nutrient and fermentation broth of algicidal strain Pseudoalteromonas QF1 caused a massive death of K. mikimotoi and substantial changes in the coexisting microbial community, in which Rhodobacteraceae and Phaeodactylibacter significantly decreased, while Halomonas and Alteromonas increased. Core operational taxonomic units (OTUs) analysis indicated that 13 OTUs belonging to Rhodobacteraceae, Maritimibacter, Marivita, Nisaea, Phaeodactylibacter, Citreicella, Halomonas, Alteromonas, Marinobacter, Muricauda , and Pseudoalteromonas dominated the changes of the microbial communities observed in the K. mikimotoi culture with or without treatments. Collectively, this study indicated that microbial community inhabiting K. mikimotoi culture includes potential algicidal bacteria, and improves our knowledge about microbial community succession during biocontrol of K. mikimotoi via nutrient stimulation or by adding isolated algicidal strains.