On applicability of a cell proliferation assay to examine DNA concentration of uv-and chlorine-treated organisms – A rebuttal of Molina et al. (2019)

In their 2019 study, Molina et al. evaluate a cell proliferation assay that fluorescently quantifies DNA for assessing ballast water treatment efficacy of organisms ≥ 10 to 50 µm. Because of concerns with the overall experimental design, procedures, and authors’ interpretations, their conclusions do not appear to be justified and the assay used to arrive at those conclusions is not proven appropriate. Specific concerns we highlight include UV and chlorine dose calculations and exposure conditions, bacterial contamination issues, poor agreement between controls, high detection limit of the assay, and mismatch between conclusions in the abstract and statistical significance of the data. Their conclusions that “population maintenance or growth was evident … after UV treatment” and “photoreactivation could have been attributed to increased mean DNA concentrations” are therefore not scientifically defensible without further experimentation and verification. These concerns call into serious question the use of this study by the US Coast Guard or other governing bodies to (1) determine the applicability of this cell proliferation assay for assessing ballast water disinfection or (2) make conclusions regarding the suitability of UV treatment for inactivating organisms in ballast water.