Assessing the impact of UV-C exposure on pre-existing cultured marine diatom biofilms

Ultraviolet-C (UV-C) has been considered as a potential tool in the maintenance and prevention of marine biofouling. However, it is unclear how irradiation disturbs biofouling, specifically biofilms, or the duration and frequency needed to reduce or eliminate their growth. The marine diatom, <i>Navicula incerta</i>, was used in a two-part lab study to determine the minimum time between UV-C duty cycling (also known as interval testing) that would result in the reduction and prevention of marine biofilms. The first study assessed the diatom's metabolic activity, morphology, behavior, and recovery to understand the influence of UV-C on the biofilm. Cell viability, biofilm matrixes, and chlorophyll <i>a</i> were significantly reduced immediately following UV-C exposure, yet when exposure was ceased biofilms began to recover. Based on these results, the second study investigated the duty cycle duration required to limit the growth of the cultured biofilm. Duty cycle testing was able to initially deplete cell viability and chlorophyll <i>a</i>; however, in between exposures, recovery was evident. These findings indicate that shorter (10 min; 1.86 J/cm²) doses of UV-C exposures must be applied more frequently than more prolonged doses (60 min; 11.16 J/cm²) to keep biofilm formation minimal. The duty cycles established here also provide a guideline of efficacy for future studies that can be applied to biofilms in both laboratory and the field.