Consequences of Long-term Exposure to Increased Salinity on the Amphibian Skin Bacterium Erwinia Toletana

Abstract Amphibian’s skin bacterial community may help them to cope with several types of environmental perturbations, including osmotic stress caused by increased salinity. This work aimed at assessing if an amphibian skin bacterium could increase its tolerance to NaCl after a long-term exposure to this salt. A strain of Erwinia toletana, isolated from the skin of Pelophylax perezi, was exposed to two salinity scenarios (of 18g/L of NaCl): (i) long-term exposure (for 46 days; Et-NaCl) and (ii) long-term exposure followed by a recovery period, (exposure for 30 days to NaCl and then to LB medium for 16 days; Et-R). After exposure, the sensitivity of E. toletana clonal populations to NaCl was assessed by testing 6 NaCl concentrations (LB medium spiked with NaCl) plus a control (LB medium). Genotypic alterations were assessed by PCR-based molecular typing method (BOX-PCR). Results shown that tolerance of E. toletana to NaCl slightly increased after the long-term exposure, EC50 for growth were: 22.5g/L (8.64-36.4) for Et-LB; 30.3g/L (23.2-37.4) for Et-NaCl, and 26.1g/L (19.3-32.9) for Et-R. Differences in metabolic activity were observed between Et-LB and Et-R and Et-NaCl and Et-R suggesting the use of different substrates by this bacterium when exposed to salinized environments. NaCl-induced genotypic alterations were not detected. This work suggests that E. toletana exposed to low levels of salinity, activate different metabolic pathways to cope with osmotic stress. Which may be further explored to be used in bioaugmentation procedures in natural populations of amphibians exposed to salinization.