Unveiling the algicidal effects and compounds of a newly isolated algicidal Enterococcus sp. JL7

The algicidal bacteria-centered strategy represents one of the alternatives for mitigating freshwater cyanobacterial harmful algal blooms (cHABs). A new algicidal Enterococcus sp. JL7 was discovered, exhibiting a 98 % algicidal rate against Microcystis aeruginosa. No Enterococcus bacterium in literature had been reported to possess algicidal properties before this study. GC-MS identified 11 compounds secreted by JL7. Benzaldehyde, 2-ethylhexanol, 2,6-di-tert-butylhydroquinone (2,6-DTBHQ), and 2,4-di-tert-butylphenol (2,4-DTBP) were verified to have algicidal abilities. The former three report their algicidal activities for the first time. Both 2,6-DTBHQ and 2,4-DTBP demonstrated 100 % effectiveness against cyanobacteria but only 40-60 % effective against green algae, suggesting their potency specifically against cyanobacteria. The identified algicidal compounds and other metabolites might synergistically contribute to the overall algicidal efficacy of JL7. Based on the measured detrimental physiological algicidal effects in M. aeruginosa, we propose a mechanism of JL7 that involved damaging the light-harvesting apparatus and electron transport in photosystem II, which impaired CO₂ fixation. The V. fischeri assay showed that the JL7 culture is ecologically safe. The algicidal simulation experiment showed that JL7 has a promising application potential with a 100 % algicidal rate using the three levels of synthetic eutrophic waters and chlorophyll a. Overall, we offer a new bacterial resource for the biocontrol of cHABs and contribute to developing natural bacterial products as algicides.