Characterization of environmental stress response of Exiguobacterium sp. isolated from high altitude Andean wetlands.

OMAR F. ORDOÑEZ; CECILIA B. DICAPUA; NESTOR R. CORTEZ; MARIA E. FARIAS

San Miguel de Tucumán

Congreso; VII Congreso argentino de Microbiología General (SAMIGE), "Samige del Bicentenario",; 2011

Andean Wetlands undergo extreme environmental conditions such as high ultraviolet (UV) radiation, elevated salinity and the presence of toxic elements as arsenic. We present here the first study on tolerance against UV radiation, salinity, arsenic and prooxidant challenge of the Exiguobacterium sp.  N30 and S17 isolated from Lake Negra and Lake Socompa, respectively, both lakes located at 4000 meters above sea level. Exiguobacterium sp. DSM6208 from the German microbial collection was used for comparison as a control strain. In the present work we evaluate the effect of sodium cloride,  sodium arsenite or pro-oxidants on growth rates. Bacterial survival after UV radiation challenges was also studied. To evaluate the antioxidant defense of the studied strains the detoxifying enzymes superoxide dismutase (SOD) and catalase were visualized by in situ staining after native poliacrilamide gels after electrophoresis. For all three studied strains the highest growth rates were obtained at 30ºC. S17 and N30 isolates showed better growth than the collection strain in culture media supplemented with 5% NaCl. Exiguobacterium sp. N30 isolate shows good tolerance to sodium arsenite while the collection strain DSM6208 exhibited an inhibition of growth. Interestingly, the S17 isolate displays an increase of growth rate after addition of 5 mM of sodium arsenite to culture media. Exposure to UV-radiation hardly decrease survival counting of N30 isolate, while 50-60% of S17and DSM6208 cultures tolerated the challenge. Bacterial cultures subjected to pro-oxidant agents such as H2O2 and methyl viologen showed no significant differences in growth among the studied strains. A single SOD species compatible with Mn-type was visualized in all three strains. On the other hand, a more diverse electrophoretic pattern was found after catalase activity staining. Exiguobacterium sp. DSM6208 and N30 strains presented three and two catalase activity bands, respectively, while a single species was detected  in S17 isolate. This is the first report concerning tolerance against extreme environmental conditions of Exiguobacterium sp. strains from Andean wetlands.