Algicidal strain of Bacillus velezensis IMV B-7571 for controlling harmful algal blooms

Abstract

Microorganisms and their metabolites hold promise as bioagents for controlling harmful algal blooms (HABs), providing an alternative to traditional chemical and physical methods. A strain of Bacillus velezensis with algіcidal activity against various cyanobacterial strains, particularly those from the genera Microcystis and Anabena was previously isolated from soil. This study aims to identify the metabolites responsible for the algicidal effectiveness of B. velezensis IMV B-7571. Transmission electron microscopy (TEM) analysis revealed significant morphological changes in the cells of Microcystis aeruginosa and M. pulverea after treatment with the supernatant from Bacillus velezensis. Notable alterations included the loss of cytoplasmic granularity, carboxysomes, and polyphosphate granules disappeared. However, the cell membrane remained intact, maintaining its integrity and reducing the risk of cyanotoxin release into the environment. Chlorophyll-a (Chl-a), a key marker for cyanobacterial growth, significantly decreased after treatment with B. velezensis supernatant compared to Ch-a levelin the control group. The algicidal ratio reached 74 %, demonstrating a strong inhibitory effect on photosynthesis after 48 h. B. velezensis IMV B-7571 was found to produce 21 different metabolites, including 11 cyclic dipeptides, with Cyclo-(Leu-Pro) and Cyclo-(Phe-Pro) being the most prominent. The purified metabolites fraction exhibited potent algicidal activity against M. aeruginosa, M. pulverea, and A. hassalii. These findings support using of B. velezensis IMV B-7571 as a sustainable and eco-friendly approach to managing harmful algal blooms.