Impact of the ultraviolet radiation on two isolated Antarctic marine bacteria

HERNÁNDEZ, E.A., G.A. FERREYRA AND W.P. MAC CORMACK

Reports on Polar and Marine Research

Año: 2008 vol. 571 p. 311 - 319

The annual depletion of the ozone layer selectively reduces absorption of ultraviolet- B radiation (UVB, 280-320 nm), resulting in higher UVB irradiance on the Antarctic surface (Staehelin et al. 2001). It was reported that the UVB is responsible of significant detrimental biological effects on aquatic environments (Vincent and Neale 2000, Booth et al. 2001a, Biggs and Moody 2003). Ultraviolet A radiation (UVA, 320-400 nm) may also be responsible for certain types of photobiological damage (Kim & Watanabe 1994, Sommaruga et al. 1997). UVA can affect bacterial viability and activity (Helbling et al. 1995), either directly or indirectly via production of oxidant compounds from dissolved organic matter. However, the major part of the studies dealing with the effect of UV radiation (UVR) on aquatic organisms has been focused on phytoplankton assemblages, the effect on the aquatic bacteria being less investigated. Bacteria play a key role in mineralization of nutrients and provide a trophic link to higher organisms (Azam et al. 1983; Ducklow et al.1992). This role is crucial in the Southern Oceans, where phytoplankton stocks are low and the spring algal blooms is scarce or do not develop (Karl 1993). Marine bacteria seem to be more susceptible than other planktonic organisms to the effects of UVR (Jeffrey et al. 1996). The lack of UV-protective compounds in marine bacteria other than cyanobacteria could be one of the causes of this susceptibility (Cockell and Knowland 1999). Reports about changes in species composition of marine bacterial communities under UVB stress (Arrieta et al. 2000) reflect the different sensitivity that different members of these communities has to the UVR stress. Solar radiation has not only detrimental effects on bacterioplankton. Crucial roles in DNA-damage repair has been found for UVA and PAR (Kaiser and Herndl 1997) as activators of the photoenzymatic repair mechanisms. This fact determines a complex relationship between positive and negative effects of solar radiation on marine bacteria which largely depends on the characteristics of the environments under study. In this work, two Antarctic marine bacteria were isolated from surface water at Potter Cove, Antarctica and used as biological models in different experimental designs in order to analyse their response to solar radiation exposure. In a first step, the effects of PAR, UVA and UVB on the isolated strains were evaluated at different time periods in days with different irradiance regimes. In a second step, the role of the water column as attenuating factor was analysed by exposure of the bacterial strains at three depths in the water column: surface, 1 m and 3 m. Finally, the effect of a simulated vertical mixing of 4 m h-1 on the bacterial survival was evaluated.-1 on the bacterial survival was evaluated.