Eutrophic water remediation efficiency of algicidal bacteria, Cellvibrio sp. G1 and Chitinimonas sp. G2, and their influence on microbial community structure

Algal blooms that occur periodically in rivers, lakes, and reservoirs are associated with the cumulative effects of excess nutrients from industrial and agricultural development. Algicidal bacteria can be used as environmentally friendly biocontrol agents to manage harmful algal blooms in eutrophic water. However, there is still a dearth of studies on the effects of mixed algicidal agents, the persistence of algae removal efficiency, and the impacts on native aquatic microbial communities. Two strains of algicidal bacteria, Cellvibrio sp. G1 and Chitinimonas sp. G2, were previously isolated and purified from reservoir sediment. Herein, G1 and G2 broth cultures, alone and in combination (1:1, V/V), were added to eutrophic water collected from a park at the volume ratio of 5 %. Eutrophic water remediation efficiency under different treatments was monitored for 30 days, and microbial community dynamics in water were analyzed by full-length sequencing of the 16S rRNA genes. The best algae removal efficiency was observed in the water treated with G1 alone, as indicated by the highest algae removal rate of 41.3 %. The total nitrogen removal rates of G1, G2, and their combination were 33.47 %, 23.65 %, and 28.88 %, respectively; ammonia-nitrogen removal rates were 24.11 %, 25.02 %, and 19.63 %, respectively; total phosphorus removal rates were 24.11 %, 25.02 %, and 19.63 %, respectively; and orthophosphate removal rates were 46.11 %, 44.37 %, and 27.92 %, respectively. In the water treated with G1 and/or G2, the major genera with algicidal capacity (i.e., Cellvibrio and Chitinimonas) were outcompeted by the well adapted genera (e.g., Pseudomonas). At the late stages of treatment, the algicidal genera decreased in relative abundance, leading to decline in algae removal efficiency and increase in chlorophyll concentration. Based on both eutrophic water remediation efficiency and environmental adaptability, G1 alone was superior to G2 alone or in combination with G1, thus having potential practical implications.