The water column as attenuating factor of UV-induced bacterial mortality in Antarctica

Full text: The increase in UV-B radiation (280-320 nm) caused by ozone depletion affect the activity of aquatic microorganisms principally heterotrophic bacteria. The aim of this research was to study the effects of solar UV-B and UV-A (320-400 nm) on two Antarctic marine bacterial strains (Cithophaga-Flavobacterium-Bacteroides group-related UVps and Arthrobacter-UVvi) in the first meters on the water column. Several assays were carried out under different irradiance conditions on Potter Cove (South Shetland Islands, Antarctica). Quartz bottles containing mixed bacterial cultures were exposed to solar radiation at 0, 1 and 3 m deep. These experiments were carried out with or without interferential filters. Results showed that the deleterious effect of solar radiation was significant at 1 m but not at 3 m deep. When filters were present, the strains showed higher mortality values under UVA+ UV-B radiation than those observed under UV-A only. When a vertical mixing of 4 m h-1 was simulated, the negative effect of UVR was reduced although a significant decrease in viability was observed in the irradiated systems compared to the dark control. Results suggested that the proposed deleterious effect of UV radiation on marine bacteria would be significant mainly in the 1 m surface layer of the Potter Cove marine water column. (author)