M. Hassanshahian; S. Ghorbani
Abstract
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 ...
Read More
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.
Nasrin Ansari; Mehdi Hassanshahian; MohammadReza Khoshro
Abstract
Introduction: Petroleum hydrocarbons are widespread pollutant that enters to soil by some pathwayssuch as: Transportation of crude oil, conservation of oil compounds, crude oil spill and treatment process on refineries. Oil pollution has some ecological effect on soil that disturbed composition and ...
Read More
Introduction: Petroleum hydrocarbons are widespread pollutant that enters to soil by some pathwayssuch as: Transportation of crude oil, conservation of oil compounds, crude oil spill and treatment process on refineries. Oil pollution has some ecological effect on soil that disturbed composition and diversity of microbial community. Also this pollution has some effects on microbial activity and enzymes of soil. Forests ecosystems may be polluted with petroleum hydrocarbons via different ways such as transportation and spill of crude oil from resource of petroleum storage. Industrial soil defined as the soils that located in industrial area such as petrochemical plant, mine, chemical factories and etc. These soils always contaminated to many pollutant such as: oil, diesel and heavy metals. These pollutants have some effects on the texture of the soil and microbial community. The aim of this research is to understand the effect of oil pollution on two different soils.
Material and Methods: In order to evaluate the effect of crude oil on soil microbial community, two different soil samples were collected from industrial and forest soils. Six microcosms were designed in this experiment. Indeed each soil sample examined inthree microcosms asunpolluted microcosm, polluted microcosm, and polluted microcosm with nutrient supply of Nitrogen and PhosphorusSome factors were assayed in each microcosm during 120 days of experiment. The included study factors were: total heterotrophic bacteria, total crude oil degrading bacteria, dehydrogenase enzyme and crude oil biodegradation. For enumeration of heterotrophic bacteria nutrient agar medium was used. In this method serial dilutions were done from each soil and spread on nutrient agar medium then different colonies were counted. For enumeration of degrading bacteria Bushnel-Hass (BH) medium were used. The composition of this medium was (g/lit): 1 gr KH2PO4, 1gr K2HPO4, 0.2 gr MgSO4.7H2O, 0.02 gr CaCl2, 1 gr NH4NO3, and two drops of FeCl3 60% , the pH was 7. The carbon source of this medium was crude oil (1%). In MPN method microplates (24 well) were utilized and turbidity was calculated as positive index.
Results and Discussion: The results of this study showed that the highest quantity of heterotrophic bacteria was related to forest soil (8 × 108). The quantities of degradative bacteria significantly were lower than heterotrophic bacteria in all soil microcosms. This result may be expected because heterotrophic bacteria can use other carbon sources instead of crude oil such as organic carbon, suger and some nutrients that exist in the soil, but degrading bacteria have some limit in the use of organic carbons and only capable to use crude oil hydrocarbons. Sothe quantity of these bacteria is lower than heterotrophic bacteria. The quantity of degradative bacteria have decrement pattern until 60th day of experiment but after this day these bacteria have increment pattern. This result can be interpreted as from beginning of experiment until 60th day of experiment the bacteria adapted to toxic effect of crude oil and after this time the quantity of bacteria increased and have ability to use pollutant in the soil. The best deydrogenase activity between different microcosms related to polluted microcosm with nutrient. This result confirms that nitrogen and phosphorus can decrease the damage effect of crude oil on soil microbial community. The mechanism of this attenuation of toxicity effect of crude oil on microbial community can be related to enhance bioavailability of essential elements for bacteria in the soil. So after oil pollution of an area, soil supply upto nitrogen and phosphorus demand must be mentioned as a necessary practice to decrease the toxicity effect of pollutants. The highest biodegradation of crude oil in all studied soils belonged to industrial microcosm (95 %). It can be explained by adaptation theory because the bacteria in the industrial soil were better adapted to different pollutants and these bacteria have more capability for biodegradation of crude oil. By this reasonthe rate of degradation of crude oil in the industrial soil were higher than forest soil. Statistical analysis of the results showed that there was a significant correlation between MPN quantity of heterotrophic bacteria and other assayed factors. Also, forest soil seemed to have significant difference with other soils.
Conclusion: according to the obtained results by this study, it can be possibly proposed appropriate strategies for bioremediation of different studied soil types. The selection of best bioremediation strategies belong to specific types of soil. Just as this research confirmed that the type of soil plays significant role in the percentage of degradation.
