Effect of Heavy Metals on Soil Microbial Community and Mung Beans Seed Germination

Pollution of the biosphere by heavy metals has caught our attention in finding new ways to sustain, restore and manage the environment. In this context, the study was carried out to assess and determine the cumulative effect of heavy metals on soil microorganisms and seed germination, which ultimately contribute serious threats to the ecosystem. We attempted to isolate stress tolerant bacteria and fungi from the soil amended with varying concentrations of heavy metal salts including silver (Ag), zinc (Zn) and lead (Pb). The procedure describes the selection of heavy metal salts, characterization of soil, simulated pollution of soil, isolation, identification, characterization, screening and assessment of heavy metal tolerance by bacteria and fungi. Effects of varying concentrations of heavy metals on the germination of seeds (bioassay) were also taken into consideration. The data suggested that lead and silver were found to be toxic for the growth of microorganisms. The amendment of zinc in the soil up to 50mM concentration facilitated the growth of bacteria and fungi. An overall change in the microbial communities was observed in comparision with the control. Germination of seeds was favoured with increasing concentrations of zinc (50mM), which indicated the essentiality of zinc to plants. More deleterious effects on the germination of Vigna radiata (mung beans) were observed in case of silver, while moderate toxicity was observed in case of lead. Silver was found to be extremely toxic since the minimum concentration (10mM) resulted in the complete inhibition of seed germination. The seed germination in the presence of 10 and 25 mM concentration of silver was delayed for a period of 10 days but subsequent exposure to same concentration for 15 days resulted in the germination of seeds.