The effects of ultraviolet radiation on the moderate halophile Halomonas elongata and the extreme halophile Halobacterium salinarum

Both the moderately halophilic bacterium, Halomonas elongata, and the extre mely halophilic archaea, Halobacterium salinarum, can be found in hypersali ne environments (e.g., salterns). On complex media, H. elongata grows over a salt range of 0.05-5.2 M, whereas, H. salinarum multiplies over a salt ra nge of 2.5-5.2 M. The purpose of this study was to illustrate the effect th at solar (UV-A and UV-B) and germicidal radiation (UV-C) had on the growth patterns of these bacteria at varied salt concentrations. Halomonas elongat a grown on a complex medium at 0.05, 1.37, and 4.3 M NaCl was found to be m ore sensitive to UV-A and UV-B radiation, as the salt concentration of the medium increased. Halobacterium salinarum grown on a complex medium at 3.0 and 4.3 M NaCl did not show a significant drop in viability after 39.3 kJ.m (-2) of UV-A and UV-B exposure. When exposed to UV-C, H. elongata exhibited substantially more sensitivity than H. salinarum. In H. elongata, differen tial sensitivity to UV-C was observed. At 0.05 M NaCl, H. elongata was less sensitive to UV-C than at 1.37 and 4.3 M NaCl. Both bacteria showed some p hotoreactivation when incubated under visible light following both UV-A, UV -B, and UV-C exposure. Mutagenesis following UV-C exposure was demonstrated by both organisms.