CONICET | Buscador de Institutos y Recursos Humanos

UVA radiation is one of the most stressful oxidative agents that bacteria have to face in natural environments. The effect of this radiation in two Leptospirillum ferroxidans strains was studied, with the aim of comparing the behaviour of the collection strain DMS 2705 and FAM-RA2, a recent isolate from Famatina (La Rioja, Argentina), at 3869 masl. After 2 h irradiation at a fluence rate of 40 W/m2, the viability of the collection strain decreased in about 2 orders, while in the isolate FAM-RA2 viability diminished only 1 order. Levels of intracellular ROS after UVA exposure were evaluated under these conditions and even though both strains showed a significant increase of ROS production after 30 min of radiation, the relation between UVA treated cells/dark controls was about 2 fold higher in DSM 2705 strain. The effect of sublethal UVA exposure on cell growth was more pronounced in DSM 2705, which showed significant decrease in Fe2+ oxidation and growth delay, while FAM-RA2 presented no significant differences between dark controls and UVA exposed cultures. Assays of biofilm formation under sublethal UVA doses, both in acrylic and mineral coupons, showed that UVA radiation induced cell proliferation and EPS production in the collection strain DSM 2705, but not in the FAM-RA2 strain, after 24 h of exposure. Taking as a whole, these results suggest a stronger defensive system against radiation in FAM-RA2 that could involve protection against ROS. The results on biofilm formation suggest that given the higher oxidative defences of FAM-RA2 strain, the UVA dose used was not enough to trigger biofilm formation as an adaptive response. This study provide insights on an important stress factor until now not considered in acidophilic microorganisms, particularly in the case of shallow acid mine drainage waters where the influence of the radiation could be high.