Extremophile Culture Collection from Andean Lakes: Extreme Pristine Environments that Host a Wide Diversity of Microorganisms with Tolerance to UV Radiation

Abstract

A total of 88 bacterial strains were isolated from six Andean lakes situated at altitudes ranging from 3,400 to 4,600 m above sea level: L. Aparejos (4,200 m), L. Negra (4,400 m), L. Verde (4,460 m), L. Azul (4,400 m), L. Vilama (4,600 m), and Salina Grande (3,400 m). Salinity ranged from 0.4 to 117 ppm. General diversity was determined by denaturing gradient gel electrophoresis (DGGE) analysis. From the excised DGGE bands, 182 bacterial sequences of good quality were obtained. Gammaproteobacteria and Cytophaga/Flavobacterium/Bacteroides (CFB) were the most abundant phylogenetic groups with 42% and 18% of identified bands, respectively. The isolated strains were identified by sequence analysis. Isolated bacteria were subjected to five different UV-B exposure times: 0.5, 3, 6, 12, and 24 h. Afterwards, growth of each isolate was monitored and resistance was classified according to the growth pattern. A wide interspecific variation among the 88 isolates was observed. Medium and highly resistant strains accounted for 43.2% and 28.4% of the isolates, respectively, and only 28.4% was sensitive. Resistance to solar radiation was equally distributed among the isolates from the different lakes regardless of the salinity of the lakes and pigmentation of isolates. Of the highly resistant isolates, 44.5% belonged to gammaproteobacteria, 33.3% to betaproteobacteria, 40% to alphaproteobacteria, 50% to CFB, and among gram-positive organisms, 33.3% were HGC and 44.5% were Firmicutes. Most resistant strains belonged to genera like Exiguobaceterium sp., Acinetobacter sp., Bacillus sp., Micrococcus sp., Pseudomonas sp., Sphyngomonas sp., Staphylococcus sp., and Stenotrophomonas sp. The current study provides further evidence that gammaproteobacteria are the most abundant and the most UV-B-resistant phylogenetic group in Andean lakes and that UV resistance in bacteria isolated from these environments do not depend on pigmentation and tolerance to salinity.