A total of twenty-four isolates of actinobacteria from arsenopyrite, pyrite, polymetallic sulfides and magnetite from Peruvian mining zones have been used with the purpose of characterizing them by morphological, physiological and molecular studies for future biotechnological applications. 23 strains were identified as Streptomyces and1 as Actinomadura sp.95% and 70% of the strains were able to grow at pH 3.5 and pH 2, respectively. Only 19% of them were able to oxidize iron at pH 2. Also, they have been tested by growth on arsenopyrite tailings and Streptomyces sp. E1 and Streptomycesvariabilis AB5 leached 19.1 % and 15.5 % of arsenic, respectively, while the control without inoculum only showed 2.5% of leaching. Results indicate that these strains show important characteristics for leaching processes.

Mining industry is a source of wealth but also of environmental pollution in Peru. In this study 12 colonies of actinomycetes were isolated in acidic cultures from mineral ores and concentrates from mines of the Peruvian highlands. The isolates were characterized phenotypically by microscopy and growth at different conditions as pH tolerance, temperature, and sodium chloride, heavy metals resistance; ferrous iron and thiosulfate oxidation. All isolates were identified as actinomycetes based on their cultural and spore characteristics. Most of the isolates were able to grow at 8 - 45°C and pH 4 - 11. 60% of isolates grew at 10% NaCl but none of them growth at 13%. Iron oxidation was shown by 60% of isolates at pH 4, but only 25% were able to oxidize iron at pH 2. Thiosulfate oxidation was not detected in any isolate. Most of the isolates showed capacity to grow in medium with 200 ppm of Pb, Fe, Zn and 100 ppm of Cu. All of the physiological characteristics found in this work indicate the potential of these isolates as source for bioremediation and bioleaching.

The aim of this research was the selection of bacterial strains resistant to mercury, as well as to demonstrate their capacity to reduce mercury in solution when they are inoculated in pure and mixed cultures. Samples of soil from informal mining gold sites in Peru were collected and fifteen mercury resistant bacteria were isolated. Strains RM6, RM7, RM9, RM11, RM12 and RM13 were selected for their capacity to reduce mercury in solution. The six bacterial strains belong to the genus Pseudomonas. Inoculated in pure cultures, these strains reduce mercury in solution although in different percentages: RM9, RM11 an RM12 reduce 93% to 97% of the mercury, while strains RM6, RM7 y RM13 reduce 80% to 85%. The consortium of all six bacterial strains showed a mercury reduction of 84%. Approximately 91% of mercury in solution was reduced in 1 hour and this reaction was not associated to bacterial growth. Using specific primers, the merA gene was amplified from genomic DNA of the bacterial strains, which would suggest the activity of the mer operon as a mechanism of mercury resistance. Due to their ability to reduce mercury in solution, it is advisable to carry out more research on the selected strains since they could be useful in future bioremediation processes.

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Three isolates ofStreptomyces variabilis(AB5, F and K1A) and one isolate ofStreptomyces sp.(C2) were isolated of acidic cultures from mineral ores and concentrates from mines of the Peruvian highlands. The isolates were identified molecular and phenotypically and characterized by growth at different conditions as pH tolerance, temperature, and sodium chloride and heavy metals resistance.Streptomyces sp. (C2) was able to grow until 200 ppm of mercury andS. variabilis(AB5) grows in the presence of 100 ppm of mercury. The isolates AB5 and K1A ofS. variabiliswere able to grow only until 50 ppm of mercury.All strains were tested by their ability to induce germination ofLactuca sativa,Medicago sativaandPhaseolus vulgarisseeds exposed to different mercury concentrations. It was shown a significative improvement inL.sativaandP. vulgaris. InL. sativaexposed to 50 ppm of mercury, all strains were able to improve germination, root length and number of leaves. Without Streptomyces addition, they only growth until 10 ppm of mercury.Streptomyces sp.isolatehad better results in germination, root length and number of leaves ofL. sativa.The results found in this work indicate the potential of these isolates for restoration of soils polluted with mercury.