Seventeen different Azotobacter isolates/mutants were checked for their resistance to various Heavy Metals (HM) (which are predominate in contaminated wismut soil) on agar media plates containing 0.02, 0.1, 1-3 mM of Al, Pb, Ni, Cr and Cd. Wismut soil contains nearly 39 HM of different concentrations. Among 17 isolates tested, all were found to be resistant to all the metals at lower concentrations except Ni and Cd and percentage resistance was 70.6 (0.02-0.1 mM). At higher concentrations (1 mM-3 mM), isolates were positive except Ni and Cd where none of the isolates were growing. The results revealed that HM resistance property is high among Azotobacter isolates. The survival of resistant bacteria inoculated on Indian mustard (B. juncea) under green house conditions was also determined. High bacterial numbers were observed in garden soil with and without inoculation, whereas contaminted soil showed low bacterial numbers. The root and shoot weight was more in the inoculated plants grown in wismut soil compared to garden soil. Low microbial numbers in contaminated soil might be due to HM adapted bacteria have better interaction with the plant.

Biogeochemical potential of microorganisms is enormous as they help in the extraction of valuable metals from low grade ores and also help to clean up the environment. Bioremediation of Heavy Metals (HM) and pollutants is a cost-effective method and in some cases, it is the only practical way. Metal contamination in the environment can arise from the number of activities including mining and industrial waste (Van Nostrand et al., 2007). Biologically essential metals like Ca, Zn and Al in high concentrations can be naturally toxic to microorganisms as metal can disrupt the cell membranes, interfere with enzymatic reactions and denature proteins and DNA. Consequently, microorganisms exposed to HM are forced to develop resistance mechanism in order to protect cellular function. HM can also decrease microbial diversity and overall microbial numbers. That is one of the reasons for increased interest in the application of this mechanism and the use of resistant organism in bioremediation of metal-contaminated system.

Metal resistance mechanisms include trapping of the metal in the bacterial exo polysaccharide layer, pumping the metal out of the system using ATP and methylation, and making the metal more volatile. Metals cannot be degraded like organic compounds instead metal toxicity can be reduced by making them less bio available or less soluble or transforming toxic form to nontoxic forms. HM effects in microorganisms have been measured on microbial activity, diversity or culturable counts. There are also reports showing decrease in the above-mentioned properties to metal contamination. Scientists (Higham et al., 1985; Mergeay, 1995; Mengoni et al., 2001; and Van Nostrand et al., 2007) have reported an increase in resistance to metals in soil bacteria isolated from contaminated soils, this suggests that during the shift in the bacterial community, sensitive species may be eliminated while tolerant or resistant species may become dominant with the result, increased tolerance might arise as a result of exposure (Roane and Pepper, 1999). HM contamination in the environment has become a serious problem due to the increase of its discharge into the environment (Bruins et al., 2000). Natural sources as well as the anthropogenic sources account for this contamination, which has become a threat to public health. Cadmium, copper and zinc are among those HM that are being released to the environment.

Genetics & Evolution Journal, Azotobacter Spp, Metal Resistance Mechanisms, Natural Sources, Organic Compounds, Bacterial Plasmids, Mustard Seeds, Multiple Resistances, Azotobacter Mutants, Plant Parameters, Anthropogenic Sources, Microbial Numbers.