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Bacterial viability and oxidative stress
Archae adaptative response
Since several years our team is in collaboration with Sami Maalej group in Sfax University (Tunisia). In this sense, in 2007, a new thesis sudent is partially in our Lab and work specifically on trying to identify new defences against oxidative stress from Tunisian solar saltern ecosystem. The first step was to better characterize this extreme environment. The solar saltern of Sfax, central-eastern coast of Tunisia, is an artificial system consisting of interconnecting shallow ponds (20 – 70 cm depth) which extend over 1500 hectares. Adaptation to this extreme environment requires coping mechanisms providing tolerance to variable salinities from near zero to saturated and unshaded exposure to the solar UV radiation. The purpose of this study was to determine the culturable bacteria diversity in two different salt concentration ponds : the crystallizer pond (TS18 with 380 g/l NaCl) and in a concentrator pond M1 (with 240 g/l NaCl). Characterization of isolated bacteria was performed via both phenotypic and phylogenetic approaches. We observed a higher biodiversity in term of culturable bacteria in M1 compared to TS18. Moreover, whereas all TS18 isolated strains appear to be extreme halophilic archaea (genus Halorubrum), culturable strains isolated from M1 could be ranged from extreme halophilic archaea (genus Halloterigena or Halorubrum) to moderate halophilic bacteria (Pseudomendales group). In addition, UVB and H2O2 resistances of two characterized haloarchaeal and two eubacterial strains were evaluated at varied salt concentrations. We observed that archaea strains were much more resistant than eubacterial strains. Moreover, all tested strains appear to reach their optimal resistance (UVB or H2O2) for the NaCl concentration leading to the optimum growth. Altogether, our results indicated that all culturable bacteria isolated from TS18 were well adapted to this extreme environment, whereas it s was partially the case for culturable bacteria from M1.
