Dr. Wade H Jeffrey

Ultraviolet radiation (UVR) has been recognized for many years as a potential stress for organisms in a variety of environments. Decrease in phytoplankton production may result in a decline in bacterial production, which may be compounded by direct UVB effects on bacterioplankton. UVR may directly affect viruses, bacteria, phytoplankton, or zooplankton via direct DNA damage and reduced rates of production. The effects of UVR on marine bacterioplankton are investigated by using radiolabeled precursor molecules such as 3H thymidine, and 3H- or 14C-leucine. It has been shown that bacterioplankton experience significant amounts of DNA damage (CPDs) in surface waters, often twice the amount of larger eukaryotic cells. Bacterioplankton accumulate DNA damage over a solar day. DNA damage extend to depths of 10 m or more in calm waters but the amount of damage may be significantly altered by surface water mixing events. Radioimmunoassay (RIA) technique is used for the measurement of specific DNA photoproducts in the DNA of UV-irradiated cells. DNA damage results are reported per unit (megabase) DNA, and are therefore independent of the concentration of DNA present in the original sample or the amount of DNA assayed. The sensitivity of the RIA is determined by the affinity of the antibody and specific activity of the radiolabeled antigen (probe).

Most research examining the effects of UV radiation (UVR) on marine microbial communities has been directed at phytoplankton and primary production. It is now apparent, however, that other microbial trophic levels must also be considered when one is investigating the ecological impact of UVR. The importance of bacterioplankton in oceanic processes has become widely recognised. Bacteria have been found to account for up to 90% of the cellular DNA in oceanic environments (Paul & Carlson, 1984; Paul, Jeffrey & Deflaun, 1985; Coffin et al., 1990) and the role of bacteria in elemental and nutrient cycling has received extensive study (Falkowski & Woodham, 1992). Bacteria have been found to play a vital role in carbon cycling, providing significant amounts of material to higher trophic levels. Various studies have shown that bacteria consume a significant proportion of primary production, although the data are quite variable and depend on location and season (Fuhrman & Azam, 1980; Hansen et al., 1983; Cota et al., 1990; Sullivan et al., 1990).Viruses are ubiquitous and abundant in marine environments infecting bacteria, phytoplankton and heterotrophic flagellates (for reviews, see Børsheim, 1993; Fuhrman & Suttle, 1993; Bratbak, Thingstad & Heldal, 1994). While viruses are often considered to be pathogens of mammals or higher plants, it has become apparent that the 108 to 1011 viruses 1−1 that are found in marine surface waters, mostly infect marine bacteria and phytoplankton (Suttle, Chan & Cottrell, 1990; Fuhrman & Suttle, 1993).