Actinomycetes: tolerance against heavy metals and antibiotics

Abstract

Heavy metals can be both, essential as well as toxic for living beings. Micronutrients such as, Co, Fe, Mn have important role to play in living systems whereas, Pb Cd etc. pose harmful effects even at low concentrations. When these heavy metals get accumulated within the tissues of the organisms at various levels of the ecological chain, they cause decrease in the biomass and biological diversity by affecting the growth, morphology and activity of the organisms. Accumulation of heavy metals in soil also causes soil contamination, which can be overcome with the help of bioremediation. A large group of soil bacteria belonging to the Actinomycetes species are exposed to heavy metals in a variety of ways; although, they show resistance to heavy metals. The species of actinomycetes possess resistance for antibiotic synthesis as well. This makes the actinomycetes suitable agents for bioremediation. In this experiment, a total of 20 isolates from Shivpuri region of Madhya Pradesh were tested for the metal tolerance against selected heavy metals. After this, the most tolerant strains were tested to check their antibiotic susceptibility. Metal tolerance was tested by agar well diffusion method and tube dilution method. Out of the 20 isolates, Ash1, Ash 2, Ash 4,Ash 6, Ash 7, Ash 8, Ash 9, Ash 10, Ash 11, Ash 12, Ash 13, Ash 15 were resistant at 10 mM conc. of CuSo4, but their growth was inhibited at higher concentrations of metal salts. Isolates Ash 10, Ash 11, Ash 12, Ash 13, Ash 19, Ash 20 were found to be resistant at 10mM conc. of ZnSO4, but they were also inhibited at higher concentrations. For different concentrations of Pb (CH3COO)2 most of the isolates showed same level of tolerance.