Isolation and characterization of bacterial isolates algicidal against a harmful bloom-forming cyanobacterium Microcystis aeruginosa

Abstract

Algicidal bacteria Mal11-2, Mal11-5 and Mal11-10, which inhibited the growth of a harmful bloom-forming cyanobacterium Microcystis aeruginosa, were isolated from a sewage treat-ment plant. The isolate Mal11-5 was phylogenetically affiliated into the genus Pedobacter, while Mal11-2 and Mal11-10 were closely related to Bacillus aerophilus, Bacillus altitudinis and Bacillus stratosphericus with 100% identity based on 16S ribosomal RNA sequences. Co-cultivation of M. aeruginosa with the algicidal isolates showed their high algicidal activity. Mal11-5 showed the highest inhibitory effect on the cyanobacterial growth: the inhibitory effect exceeded 50% after 2 days, and reached to 75-85% after 10 days, regardless of the bacterial cell density. The cyanobacterial cells aggregated and produced mucilaginous, glycocalyx-like compounds when attacked by the algicidal bacteria. These results suggest that the algicidal bacteria isolated in the present study are potentially useful as biocontrol agents against M. aeruginosa bloom.