Bacillus subtilis A4，a potential algicidal bacterium against Spirogyra

Abstract

Abstract Spirogyra species are economically important harmful algae in aquaculture environments that have resulted in ecosystem damage and significant economic losses to fisheries. However, little information is available on Bacillus species against harmful Spirogyra. In this study, an algicidal isolate (A4) against Spirogyra was obtained from the sediment of an aquaculture pond and was identified molecularly and phenotypically as B. subtilis. It showed a wide algicidal spectrum against Spirogyra, and exhibited significant algicidal effects with algicidal ratios above 50% under the conditions of 3.0 × 106 to 3.0 × 109 CFUžmL− 1, 15°C to 35°C, and photoperiods of 14h:10h, 24h:0h and 0h:24h (light/dark). In addition, isolate A4 showed an algicidal mode of indirect attack, and was safe with an LC50 above 3.0 × 109 CFUžmL− 1 to zebrafish. To the best of our knowledge, this study is the first to characterize B. subtilis as a promising biocontrol agent against Spirogyra.