Impact of incident solar UV radiation on marine bacteria from Potter Cove, South Shetland Island, Antarctica

HERNANDEZ EA; CORIA SH; RUBERTO L; VAZQUEZ S; LOPEZ JL; MAC CORMACK WP

Cordoba

Congreso; 16th International Congress on Photobiology; 2014

Bacterioplankton plays a key role in the carbon cycle of marine ecosystems. Sensibility of marine bacteria to ultraviolet radiation (UVR) depends on the incident wavelengths and can greatly differ between strains. In this work we summarize results from a number of experiments carried out during several Antarctic summer expeditions 1999-2007. Two Antarctic marine bacteria were isolated from marine water at Potter Cove, Antarctica and used in different experimental designs in order to analyze their response to solar radiation exposure. The strains were identified by 16S rDNA sequencing as Arthrobacter sp. and Bizionia sp. Flasks containing bacterial suspensions and covered with cut-off filters were directly exposed to solar radiation on land, on the water column at fixed depths (0, 1 and 3 m) and also under simulated vertical mixing of 4 m h-1 . The following treatments were defined: Dark, PAR, PAR+UVAR and PAR+UVAR+UVBR. Both strains showed a significant loss of viability after exposure to UVBR doses >7 kJ m-2 . On land assays showed that at moderate irradiances (near 3 kJ m-2 ) Bizionia sp showed to be more sensitive to UVBR than Arthrobacter sp. Lethal dose 50 (LD 50) for Bizionia sp. was 1.2 and 2.8 kJ m-2 for 280 and 305 nm, respectively, whereas for Arthrobacter sp. were 2.3 and 4.0 kJ m-2 . When cells were maintained in the dark for different periods after solar radiation exposure, no recovery was observed. This observation suggested that repair mechanisms were not effective enough to balance UVR damage in these species. Response of the strains in the stratified water column was similar to those observed on land, but the impact caused by UVR was only detected in the first meter depth. Furthermore, these effects showed some degree of attenuation when the strains were exposed to simulated conditions of vertical mixing.