Diverse Responses to UV-B Radiation and Repair Mechanisms of Bacteria Isolated from High-Altitude Aquatic Environments

Acinetobacter johnsonii A2 isolated from the natural community of Laguna Azul (Andean Mountains at 4,560 m above sea level),Serratia marcescens MF42,Pseudomonas sp. strain MF8 isolated from the planktonic community, andCytophaga sp. strain MF7 isolated from the benthic community from Laguna Pozuelos (Andean Puna at 3,600 m above sea level) were subjected to UV-B (3,931 J m−2 ) irradiation. In addition, a marinePseudomonas putida strain, 2IDINH, and a secondAcinetobacter johnsonii strain, ATCC 17909, were used as external controls. Resistance to UV-B and kinetic rates of light-dependent (UV-A [315 to 400 nm] and cool white light [400 to 700 nm]) and -independent reactivation following exposure were determined by measuring the survival (expressed as CFU) and accumulation of cyclobutane pyrimidine dimers (CPD). Significant differences in survival after UV-B irradiation were observed:Acinetobacter johnsonii A2, 48%;Acinetobacter johnsonii ATCC 17909, 20%;Pseudomonas sp. strain MF8, 40%; marinePseudomonas putida strain 2IDINH, 12%;Cytophaga sp. strain MF7, 20%; andSerratia marcescens , 21%. Most bacteria exhibited little DNA damage (between 40 and 80 CPD/Mb), except for the benthic isolateCytophaga sp. strain MF7 (400 CPD/Mb) andAcinetobacter johnsonii ATCC 17909 (160 CPD/Mb). The recovery strategies through dark and light repair were different in all strains. The most efficient in recovering were bothAcinetobacter johnsonii A2 andCytophaga sp. strain MF7;Serratia marcescens MF42 showed intermediate recovery, and in bothPseudomonas strains, recovery was essentially zero. The UV-B responses and recovery abilities of the different bacteria were consistent with the irradiation levels in their native environment.