The Secondary Outbreak Risk and Mechanisms of Microcystis Aeruginosa after H2O2 Treatment

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H 2 O 2 ) is an algaecide widely used in practice, but similar re -bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa ( M. aeruginosa ) temporarily hibernates after H 2 O 2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L -1 and 20 mg L -1 H 2 O 2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re -bloom had undergone two stages including first recovery and then re -division. The expression of fts Z and fab Z genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H 2 O 2 treatment. The findings suggest that optimizing the dosage and frequency of H 2 O 2 , as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.