Algal DNA repair kinetics support culture-based enumeration for validation of ultraviolet disinfection ballast water treatment systems

To mitigate the potential spread of invasive species and pathogens, the International Maritime Organization and U.S. Coast Guard (USCG) adopted discharge performance standards for ballast water management that will take full effect in 2017. The USCG requires staining methods for enumerating ballast water treatment system (BWTS) efficacy. These stains do not detect DNA damage, the primary mechanism for ultraviolet (UV) disinfection, and neglect potential DNA repair after discharge. These factors necessitate investigation of enumeration methods for accurate validation and approval of UVbased BWTSs. To molecularly assess DNA damage and repair kinetics, UV-induced DNA lesions were quantified by an enzyme-linked immunosorbent assay in Tetraselmis suecica control and UV-treated samples that were cultured and tested over time. Most DNA repair occurred within 6 h, was essentially complete within 24 h, and was insensitive to light or nutrient conditions during incubation. Asymptotic repair kinetics indicated a maximum of 67% of DNA damage inflicted by 300 mJ/cm² was repairable. These data provide a novel UV dose response for DNA damage in T. suecica and indicate that enzymatic DNA repair kinetics are not affected by culture conditions. Because DNA is rapidly photorepaired, culture-based enumeration can be used to accurately validate UV BWTSs.