Optimizing UVA and UVC synergy for effective control of harmful cyanobacterial blooms

Harmful cyanobacterial blooms(HCBs)pose a global ecological threat.Ultraviolet C(UVC)irradiation at 254 nm is a promising method for controlling cyanobacterial proliferation,but the growth suppression is temporary.Resuscitation remains a challenge with UVC application,necessitating alternative strategies for lethal effects.Here,we show synergistic inhibition of Microcystis aeruginosa using ultraviolet A(UVA)pre-irradiation before UVC.We find that low-dosage UVA pre-irradiation(1.5 J cm^(−2))combined with UVC(0.085 J cm^(−2))reduces 85%more cell densities compared to UVC alone(0.085 J cm^(−2))and triggers mazEF-mediated regulated cell death(RCD),which led to cell lysis,while high-dosage UVA pre-irradiations(7.5 and 14.7 J cm^(−2))increase cell densities by 75-155%.Our oxygen evolution tests and transcriptomic analysis indicate that UVA pre-irradiation damages photosystem I(PSI)and,when combined with UVC-induced PSII damage,synergistically inhibits photosynthesis.However,higher UVA dosages activate the SOS response,facilitating the repair of UVC-induced DNA damage.This study highlights the impact of UVA pre-irradiation on UVC suppression of cyanobacteria and proposes a practical strategy for improved HCBs control.