Algae control in oligotrophic surface water under the joint effect of nutritional competition and microbial algae-lytic substances
Harmful algal abnormal proliferation presents the most severe threat to the quality of oligotrophic surface water even in source water such as the South-to-North Water Diversion Project in China. A novel strategy based on an algae-lysing bacterium, Bacillus velezensis V4, and PHA was proposed to control algae in oligotrophic surface water. HPLC-MS results indicated that strain V4 could produce and release bacilysin to lyse algal cells. An algae-inhibiting agent, termed PHA–starch (V4), was prepared by growing V4 on the surface of solid carbon source PHA–starch granules, and tested for its algal control efficiency using two oligotrophic surface water samples with abnormal algal proliferation. The results demonstrated that cells of Chlorella sp. and Scenedesmus sp. were lysed after treating with PHA–starch (V4), resulting in the release of intracellular components into the surrounding environment. Additionally, NO3−-N was reduced from ∼1.77 to ∼0.3 mg L−1, accompanied with low NH4+-N and NO2−-N, and above 79% abatement of low-nitrate-N was observed in both South-to-North water and Stormwater, which achieved algae inhibition by means of nutritional competition. Under the combined effect of nutritional competition and bacilysin lysis, a 97% decline in chlorophyll-a content was achieved in South-to-North water and 61.5% in Stormwater. These results indicated that the strategy based on PHA and algae-lysing bacteria for algal control has great potential to deal with algal abnormal proliferation in oligotrophic surface water.