© 2013 PP House Isolaion of Heavy Metal Resistant Bacteria for Sustainable Crop Producion Soumitra Nath 1* , Indu Sharma 2 , Bibhas Deb 1 and Virender Singh 3 1 Bioinformaics Centre, Gurucharan College, Silchar, Assam (788 004), India 2 Department of Microbiology, Assam University, Silchar, Assam (788 011), India 3 Himachal Insitute of Life Sciences, Ponta Sahib, H.P (173 025), India 000 266 International Journal of Bio-resource and Stress Management 2013, 4(2):266-269 Abstract Article History Correspondence to Keywords Manuscript No. c103 Received in 30 th August, 2012 Received in revised form 14 th May, 2013 Accepted in inal form 6 th June, 2013 Thirty ive heavy metal resistant bacteria were isolated from contaminated crop ield of Southern Assam, India, against copper, zinc, cadmium and lead. The predominant isolates were identiied as Proteus sp., Klebsiella sp., Staphylococcus sp., Bacillus sp. and Pseudomonas sp.. Some isolates exhibited high resistance to heavy metals with minimum inhibitory concentration (MIC) for heavy metals as 60 μg ml -1 (for copper), 180 μg ml -1 (for lead) 130 μg ml -1 (for cadmium) and 1800 μg ml -1 (for zinc). They also showed multiple heavy metal tolerance and were multi-antibiotic resistant. There was decrease in total count and microbial population diversity with increasing metal concentrations. The present study showed a correlation between heavy metal resistance and antibiotic tolerance among bacterial isolates. The effect of heavy metal resistant strains on Oryza sativa inoculated in contaminated soil showed a remarkable increase in the shoot length when compared with control pots. * E-mail: nath.soumitra1@gmail.com Heavy metal, MIC, antibiotic tolerance, rhizosphere. 1. Introduction The quality of life on earth is inextricably linked to overall quality in the environment. The pollution of the ecosystem by heavy metals is a real threat to the environment because metals cannot be degraded like organic pollutants and persist in the ecosystem having accumulated in different parts of the food chain (Igwe et al., 2005). The use of domestic and industrial efluents, which may contain high concentrations of heavy metals on agricultural lands, is a common practice in some parts of the world. These toxic metals, when concentrated on plant tissues can have damaging effects on the plants themselves and may also pose health hazards to man and animals (Kumar et al., 2010). Heavy metals become toxic when they are not metabolized by the body and accumulate in the soft tissues. It is important to study the indigenous microorganisms in heavy metal polluted sites. Excessive accumulation of heavy metals in agricultural soils through wastewater irrigation, may not only result in soil contamination, but also lead to elevated heavy metal uptake by crops, and thus affect food quality and safety (Muchuweti et al., 2006). Microorganisms are generally the irst to be affected by the discharges of heavy metals into the environment. Microbial ecosystem can drastically alter the fate of the metal entering into aquatic or soil environments (Brown, 1996). Yeast, fungi, algae, bacteria and some aquatic plants have been reported to have the capacity to concentrate metals from dilute aqueous solutions and to accumulate them inside the cell structure (Modak et al., 1996). In order to survive in heavy metal polluted environments, many microorganisms have developed resistance to toxic metal ions. These mechanisms include: metal exclusion by permeability barriers, active transport of the metal away from the cell organism, intracellular sequestration of the metal by protein binding, extracellular sequestration, enzymatic detoxiication of the metal to a less toxic form and reduction in metal sensitivity of cellular targets (Bruins et al., 2000). The detoxiication mechanisms may be directed against one metal or a group of chemically related metals. Furthermore, the detoxiication mechanisms may vary depending on the type of microorganism. This transformation of the contaminant is an incidental reaction catalyzed by enzymes present in the cell’s metabolic system (Prasenjit and Sumathi, 2005). The objectives of this study were to investigate heavy metal stress on bacteria, isolated from contaminated sites of Cachar district of Assam, India and to evaluate the bioremediation potential of the strains for better crop improvement. 2. Materials and Methods 2.1. Isolation and identiication of bacteria