Removal of harmful algae by sp. H3 and sp. H5: algicidal pathways and characteristics.

Application of algicidal bacteria is a promising technology to control harmful algal blooms (HABs). In this study, algicidal bacteria strains sp. H3 and sp. H5 were obtained via two different isolation methods from the same lake water sample, with optimal algicidal efficiencies 96% and 74% against algae mixture. The sp. H3 and sp. H5 lysed algae cells through cells-to-cells direct contact and secretion of algicidal metabolites, respectively. The stronger algicidal capability of sp. H3 was also attributable to its higher efficiency for triggering reactive oxygen species, which led to broken down of the antioxidant system and more severe damage to the bacterial cells. The antioxidant enzyme activities in sp. H5 group were still expressed because of its relatively weaker algicidal capability and some intact algal cells were remained. The liquid carbohydrates from algal lysis in both groups increased significantly, whereas the quantities of liquid protein decreased, which might be assimilated by algicidal bacteria. Nonetheless, the whole algicidal process resulted in the increase of total released organic matters content. This study revealed the algicidal pathways of diverse bacterial strains, and the possible secondary environmental problem caused by the algal released organic matters should be considered when applying bacteria to control HABs.