عنوان مقاله [English]
Introduction: One of the most important indicators in relation to industry, economy and environment is to achieve the most recovery with the least cost and minimum pollution. Today, the use of chemolithotrophic microorganisms is common for extraction of some metals such as cooper, uranium, gold, cobalt and molybdenum in bioleaching process of low-grade rocks. Attention to the bioleaching of heavy metals such as copper, nickel, cobalt, zinc, and molybdenum has been increased in recent years because of its application to low-grade ores. The variety of microbes identified as being capable of growth in situations that simulate bio-mining commercial processes is rapidly growing. This is partly because of an increase in the number of environments being screened for such organisms, partly because of an increase in the variety of minerals being tested, and most importantly because of new techniques available to screen for the presence of organisms. The aim of the present research was to study the quantity of two important autotrophic bacteria, iron and sulfur oxidizing bacteria, in different regions of Miduk mine in Shahrbabak, Kerman province.
Materials and Methods The soil samples were collected from different locations of Miduk cooper mine such as: Sulfuric Pool Acid Discharge (PAD), Oxidic PAD, Sulfuric damp, Pool Leaching Sulfuric (PLS)and leaching hip. Top layer of mine soil (about 1 cm) was removed. In each site, soil samples were collected from five different spots. The quantity of iron and sulfur oxidizing bacteria were measured by culture of serial dilutions of samples in 9K medium with Iron and sulfur as electron sources, respectively. The 9K medium was used for enrichment of iron and sulfur oxidizing bacteria in collected mine samples. These two important groups of bacteria have autotrophic growth but the energy sources for these two bacteria are different. Iron oxidizing bacteria use ferrous ion in form of FeSO4 but sulfur oxidizing bacteria use inorganic sulfur and sulfur compounds as a source of energy and obtain the carbon from the reduction of the CO2 of the atmosphere, in autotrophic growth. Heterotrophic bacteria were quantified by culture in nutrient broth medium. Most probable number (MPN) method was used to enumeration the autotrophic and heterotrophic bacteria by culture of samples in 24 well microplates with specific medium. The positive index for enumeration iron and sulfur oxidizing bacteria in these experiments were red color and turbidity, respectively. The microplates were incubated for 21 days for autotrophic bacteria and 7 days for heterotrophic bacteria.
Results and Discussion: The results of this research showed that the highest quantity of heterotrophic bacteria related to soil near to PLS and the lowest quantity belonged to sulfuric PAD. Iron oxidizing bacteria had the highest density on oxidizing Pad (OP) and the lowest density of these bacteria found in soil near to PLS. The diversity of iron oxidizing bacteria was low in the mine. The lowest quantity of sulfur oxidizing bacteria related to oxidizing PAD. Although appropriate diversity of sulfur oxidizing bacteria in compare to iron oxidizing bacteria was observed in the Miduk mine. These results about quantity of iron oxidizing bacteria confirmed this truth that the presence of oxygen and also low acidity in oxidizing Pad (OP) has major effect on the distribution and quantity of iron oxidizing bacteria. Because, the optimum condition for growth of iron oxidizing bacteria is low acidity and abundance of oxygen that these two factors provided in oxidic Pad (OP).
The quantity of sulfur oxidizing bacteria was high in yellow soil near to PLS. These results obtained by enumeration with MPN and Newbar lam methods. This result can be interpreted as the high concentration of sulfur element in this region has a selection force to prevalent the sulfur oxidizing bacteria in compare to iron oxidizing bacteria in this region. Because, when the sulfur is high, the bacteria that can use this element as their only energy source for fixation of CO2 is dramatically increased.
Conclusions: In the present research, the quantity and distribution of iron and sulfur oxidizing bacteria of Miduk cooper mine were studied. Based on the results, iron and sulfur oxidizing bacteria had the highest density on oxidizing Pad (OP) and in yellow soil near to PLS, respectively. Although sulfur oxidizing bacteria had an appropriate diversity compared to iron oxidizing bacteria in Miduk mine. However, the results obtained in this study confirmed that the sufficient quantity of iron and sulfur oxidizing bacteria were present in this mine. Then, the soil bacteria of this mine can be used to enhance the bioleaching process in Miduk mine.