Microbial Diversity in Heavy-metal Polluted Waters

Indigenious water microflora as well as the presence of metaland xenobiotic biotransforming bacteria were investigated in waters near the KCM Pb-Zn smelter, South Bulgaria. Content of As, Hg, Cd, Mn, Pb, Cu and Zn exceeded in times the maximum permission standart. Absence of some microbial groups demonstrated a change in the microbial community structure in the region. Ecotoxicology test ISO/DIS 10712.2 displayed toxic environmental effect of the polluted waters, especially one of them which demonstrated 72 % ofn ecotoxicity. More than 20 ecologically relevant new bacteria were cultured. Three of them demonstrated tolerance to Cd, Cu and Mn and fivea tolerance to 2,4-dichlorphenoxyacetic acid. Our result revealed that the heavy metal pollutions reduced the microbial diversity in the studied waters, are ecotoxic as well as that some of newly isolated bacteria possess a capacity for a clean-up biotechnologies in the region. Introduction Microbial-metal transformations represent a key component to metal cycling in natural systems (14, 22). Metal transformations in the environment are dominated by redox reactions, complexation of organic and inorganic compounds and cycling among soluble and insoluble forms (3). Moreover bacterial cells living in extreme metal concentrations possess an essential for their survival ability to resist such stress (5, 19) The ability of microorganisms to grow in the presence of high metal concentrations results from specific mechanisms as: extracellular precipitation and exclusion of metal ions, binding of the metal ions to the outer surface of bacteria and its intracellular sequestration. Binding of metal cations on the surface of bacterial cells has become one of the most attractive means for metal biotranformation. Those metals which possess electron configurations containing 10 to 12 outer-shell electrons are often toxic to organisms at relatively low concentrations. This group of metals include Hg2+, Ag+, Cu+, Cd2+, Zn2+ and Pb2+ (18). At higher concentrations heavy-metal ions form unspecific complexes in the cell, which lead to toxic effects for human health (20). Metal-microbe interactions have an important role in several biotechnological applications including biomineralization, bioremediation, bioleaching and microbial corrosion and have gained growing attention in recent years (10). This development include the use of indigenious isolates as pure cultures or microbial consortia that are capable to mobilize and immobilize metal ions. Extremely difficult for bioremediation are the co-contaminated with metals and pesticides environments. Phenolic pesticides are hazardous and exhibit acute or chronic toxicity (23). Several genetic mechanisms may contribute to the adaptive response of bacteria to them (27). The problem of pollution with mixed wastes,