Bacteriological control by Raoultella sp. R11 on growth and toxins production of Microcystis aeruginosa

Microcystis aeruginosa is a cyanobacterium that can cause harmful algal blooms (HABs) in freshwater bodies. In this study, the bacterium Raoultella sp. R11 was evaluated for its ability to control the growth of M. aeruginosa. Algal growth, denitrification activity, and toxin production were measured in the presence of various concentrations of Raoultella sp. R11. The algicidal effects of Raoultella sp. R11 were studied by measuring the zeta potential (surface charge), the activity of superoxide dismutase (SOD), and the concentrations of chlorophyll-a, dissolved organic matter, and microcystin-LR in algal cultures. The results suggested that chlorophyll-a removal, which indicates algal death, was correlated with the dose of Raoultella sp. R11. The zeta potential and denitrification activity decreased in the presence of bacteria in a dose-dependent manner. SOD activity was correlated with the inoculation dosage of Raoultella sp. R11. Using a 30% (v/v) dose of bacterial culture, the removal efficiency of chlorophyll-a was as high as 94.28% after 6 days. In addition, dissolved microbial metabolites and humic acid were detected in high quantities whereas low quantities of protein-like substances and fulvic acid were found. Furthermore, toxic microcystin-LR produced by the algae was eliminated at up to 92.21% efficiency. A high denitrification rate (1.57 mg NO3--N L^-1 h^-1) and chlorophyll-a removal efficiency (73.12%) were observed within 6 days at an inoculation dosage of 20% (v/v) of bacterial culture. Our findings indicated that Raoultella sp. R11 has a high potential for applications in simultaneously controlling M. aeruginosa and facilitating denitrification in freshwater bodies.