Applicability of a cell proliferation assay to examine DNA concentration of UV- and chlorine-treated organisms.
Ultraviolet radiation (UV) and total residual oxidant (TRO) treatments have been used to control microorganisms in drinking water, and are commonly used in ballast water management systems designed to reduce the transport and delivery of invasive organisms. Because treatments may not result in immediate cell death but may render organisms unable to reproduce, standard approaches to determine if a cell is living or dead (i.e., based on movement or cellular function) may not identify treated organisms. This scenario particularly applies to UV-treated cells that are rendered non-viable but still living. Thus, alternative approaches are needed to determine an organism's viability (ability to reproduce). This study evaluated a cell proliferation assay measuring DNA concentrations in 96-well plates to determine proliferation of UV- and chlorine-treated organisms. Treatments included UV doses of 300 and 800 mWs cm-2 or an applied ClO- concentration of 10 mg L-1. To determine optimal cell proliferation thresholds and detection limits, two phytoplankton species, Tetraselmis marina (UV and ClO-) and Prorocentrum micans (ClO-), were evaluated immediately following treatment and after 1-, 5-, and 14-day incubations in light or dark conditions. T. marina exhibited cell proliferation in all UV treatments, although no cell proliferation was detected for T. marina or P. micans in any ClO- treatment. This type of assay allows for increased sample replication, smaller sample volumes, quicker preparation, and faster measurement than traditional growth assays. In conclusion, DNA staining assays may be useful to detect changes in cell proliferation over time in the context of ballast water testing.