Isolation and characterization of a Facultative chemolithotrophic sulphur and iron oxidizing bacterium from Ardabil acidic springs

Abstract

Introduction: Since metal extraction from sulfide ores by physicochemical methods is expensive and also detrimental to the environment, microorganisms, mainly bacteria are being increasingly used for desulfurization of sulfide minerals. Microbial leaching or bioleaching is an inexpensive and environmentally friendly technology for metal recovery.Materials and Methods: In the present study, to isolate iron and sulfur-oxidizing bacteria which are active in bioleaching process, spring water samples were collected and enriched by iron and sulfur-containing media. In order to identify the isolated bacteria, several morphological, physiological, biochemical and 16S rDNA phylogenetical methods were implemented. Results: After several sub-cultures, a gram-positive spore-forming rod (NS strain) was isolated and then characterized. Sequence analysis of 16S rDNA revealed that the isolated strain was closely related to Bacillus firmus strain IAM 12464 (99%), that was capable to oxidize several sulphur and iron component such as: thiosulfate 5%, elemental sulphur 3%, sodium sulphate 3%, pyrite 3%, pyrrhotite 3%, ferrous sulphate 4.5% and Iron powder 2%. Also, this isolate could dissolve copper of SARCHESHME ore to copper sulphate and change the colour of medium to blue-green. The optimal growth of the isolate was observed at 25°C and pH 4. Discussion and Conclusion: Due to the optimum pH and temperature, and the iron and sulphur oxidizing activity of this isolate, this bacterium together with a consortium of lithotrophic bacteria could be used in bioleaching processes.