Ultraviolet-A (UVA) radiation is one of the most stressful oxidative agents that bacteria have to face in natural environments. The effect of this radiation on growth, survival, biofilm formation, and bioleaching activity of two Leptospirillum ferrooxidans strains was studied, comparing the collection strain DSM2705 with FAM-RA2, a strain recently isolated from Famatina (La Rioja, Argentina), at 3869 m above sea level (ma.s.l.). We demonstrated that the isolate FAM-RA2 was more UVA resistant than the collection strain DSM2705 in kinetic growth and biofilm formation assays. However, both strains presented a similar behavior in their bioleaching capacity. Higher levels of intracellular reactive oxygen species (ROS) after UVA exposure were detected in DSM2705 strain, suggesting the presence of stronger defensive mechanisms against oxidative stress in FAM-RA2 strain. Assays of biofilm formation showed that UVA radiation induced cell adhesion and extracellular polymeric substance (EPS) production in the collection strain DSM2705, but not in the FAM-RA2 strain. The ability of UVA radiation to increase biofilm formation in DSM2705 led us to suppose that this agent could promote its bioleaching activity; however, under these studied conditions, this stress agent did not enhance metal sulfide dissolution. This study provides first insights into the effects of UVA radiation on the physiological features of acidophilic microorganisms.

紫外线-A（UVA）辐射是细菌在自然环境中必须面对的压力最大的氧化剂之一。辐射对两种铁氧体钩端螺旋体的生长，存活，生物膜形成和生物浸出活性的影响对这些菌株进行了研究，将收集菌株DSM2705与最近从Famatina（阿根廷拉里奥哈）分离的FAM-RA2菌株在海拔3869 m处进行了比较（ma.sl）。我们证明，在动力学生长和生物膜形成测定中，分离株FAM-RA2比收集菌株DSM2705更耐UVA。但是，两种菌株在其生物浸出能力方面均表现出相似的行为。在DSM2705菌株中，UVA暴露后检测到较高水平的细胞内活性氧（ROS）水平，表明FAM-RA2菌株中存在较强的防御氧化应激的防御机制。生物膜形成的测定表明，UVA辐射在收集菌株DSM2705中诱导了细胞粘附和细胞外聚合物质（EPS）的产生，但在FAM-RA2菌株中则没有。UVA辐射增加DSM2705中生物膜形成的能力使我们认为该试剂可以促进其生物浸出活性。但是，在这些研究条件下，该应力剂并未增强金属硫化物的溶解。这项研究提供了对UVA辐射对嗜酸微生物生理特性影响的初步见解。