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

HERNÁNDEZ, EDGARDO A; CORIA, SILVIA H.; RUBERTO, LUCAS A.M; VAZQUEZ, SUSANA C.; LOPEZ, JOSÉ L; MAC CORMACK, WALTER P.

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

International Union of Photobiology

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 [1] and can greatly differ between strains [2]. In this work we summarize results from a number of experiments carried out during several Antarctic summer expeditions 1999-2007 [3, 4]. 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.  [1] A. Bauermeister, E. Bentchikou, R. Moeller, P. Rettberg. Roles of PprA, IrrE, and RecA in the resistance of Deinococcus radiodurans to germicidal and environmentally relevant UV radiation. Arch Microbiol, 2009, 19, pp 913?918.  [2] A.L. Santos, V. Oliveira, I. Baptista, I. Henriques, N. Gomes, A. Almeida, A. Correia, A. Cunha.  Diversity in UV sensitivity and recovery potential among bacterioneuston and bacterioplankton isolates. Lett Appl Microbiol, 2011, 52, pp 360?366.  [3] E.A. Hernández, G.A. Ferreyra, W.P. Mac Cormack. Response of two Antarctic marine bacteria to different natural UV radiation doses and wavelengths. Antarct Sci, 2006 18 pp 205?212. [4] E.A. Hernández, G.A., Ferreyra L.A.M. Ruberto, W.P. Mac Cormack. The water column as an attenuating factor of the UVR effects on bacteria from a coastal Antarctic marine environment. Polar Research, 2009, 28, pp 390-398.