Isolation of UV-B resistant bacteria from two high altitude Andean lakes (4,400 m) with saline and non saline conditions.

Laguna (L.) Negra and L. Verde are high altitude Andean lakes located at the 4,400 m altitude in the Andean desert (Puna) in the Argentine northwest. Both lakes are exposed to extreme weather conditions but differ in salinity contents (salinity 6.7% for L. Negra and 0.27% for L. Verde). The aim of this work was to isolate ultraviolet B fraction (UV-B) resistant bacteria under UV-stress in order to determine, a possible connection, between resistance to UV-B and tolerance to salinity. DNA damage was determined by measuring CPDs accumulation. Connection among pigmentation production and UV resistance was also studied. Water samples were exposed to artificial UV-B radiation for 24 h. Water aliquots were plated along the exposition on different media, with different salinity and carbon source content (Lake medium (LM) done with the lake water plus agar and LB). CFU were counted and DNA damage accumulation was determined. Isolated bacteria were identified by 16S rDNA sequence. Their salinity tolerance, were measured at 1, 5 and 10% NaCl and their pigment production in both media was determined. In general it was found that UV resistance and pigment production were the optimum in Lake Medium done with lake water which maintained similar salinity. The most resistant bacteria in L. Negra were different strains of Exiguobacterium sp. and, in L. Verde, Staphylococcus sp. and Stenotrophomonas maltophilia. These bacteria showed the production and increase of UV-Vis absorbing compounds under UV stress and in LM. Bacterial communities from both lakes were well adapted to high UV-B exposure under the experimental conditions, and in many cases UV-B even stimulated growth. The idea that resistance to UV-B could be related to adaptation to high salinity is still an open question that has to be answered with future experiments.