Microbial diversity shifts in cyanobacteria treated with potential bacterial biological control agents.. Bacterial diversity shifts in treated cyanobacteria

The mitigation of toxic cyanobacterial blooms is a much researched and ongoing challenge. Various interventions have been researched, including the use of biological control. Bacterial isolates have been reported to degrade cyanotoxins or effectively lyse cyanobacterial cells. Mitigating cyanobacterial toxicity and the introduction of effective control methods in a mixed environment is a challenge to exploit. Subsequent toxin releases in stressed cyanobacterial cells has been indicated as an obstacle in the application of predatory bacteria. The current study investigated the changes occurring in cyanobacterial cells, related to toxin reduction and ultrastructural changes cellular damage after treatment with naturally occurring bacterial isolates. Non axenic cCultures of colonial Microcystis sp. and a filamentous cyanobacterium Oscillatoria sp isolated from dams in South Africa, were assessed over a four day period exposure to predatory bacterial isolates. Isolates 1, 3w, 3y from the phylum Proteobacteria were effective in the reduction of microcystins released by both cyanobacteria. These were compared to Lysinibacillus related isolate B, which was from the phylum Firmicutes. In conjunction to this, the changes observed in the bacterial diversity were monitored to determine the bacterial assemblage shifts caused by the treatment using next generation sequencing. Minimal diversity shifts were noted in Microcystis treated cultures, whilst Oscillatoria treated cultures indicated a greater diversity shift, indicating an increase of families containing isolates linked to bloom decline