Abstract:
Culturable bacterial profile, bacterial chromium tolerance, chromium removal efficiency, their role in plant well-being and environmental cleaning were investigated in this study. The literature survey revealed that the microbes growing in heavy metal polluted soil can furnish an impressive mode of environmental heavy metal degeneration. In order to understand the activity of microbial heavy metal tolerance, rhizospheric microbes were isolated from the soil of three hot and humid, heavy metal depository sewage reservoirs in the south (Circular Canal, Tolly Nullah), east (East Kolkata Wetland), and north (Kestopur Khal) of Kolkata. Different morphological, physiological, and biochemical characteristics and antibiotic resistance patterns were analyzed with these isolated microbes. In order to compare the composition of the bacterial community, the selected microbes were subjected to molecular characterization after fulfilled the criteria of polyphasic classification accordingly. The heavy metal resistance patterns and possible biochemical mode of action behind chromium reduction of selected microbes and their impact in reducing the chromium concentration were subsequently investigated. The microbe inhabited at anoxic to hypoxic chromium polluted sewage environment, adapted itself by such a manner that, it can utilize the redox potential of chromium reduction to fulfil its own physiological needs in the absence of oxygen. The microbe produced extracellular organic acids, chelating compounds siderophore and EPS helped in microbial chromium absorption by inducing soil chromium mobility. Soil chromium mobility also influenced the reduction of plant chromium absorption and facilitated plant growth in chromium polluted environment by means of microbial chromium affinity. The Plant Growth Promoting Rhizobacteria (PGPR)-like traits of the isolated soil microbes were investigated and their influence on rhizospheric heavy metal absorption by the plant roots was studied. Three neutrophilic mesophilic chromium resistant microbial strains (Microbacterium radiodurans K12016, Bacillus xiamenensis 1E0018 and Bacillus xiamenensis 26K018) were chosen for their selective antibiotic sensitivity and effective chromium absorption and reduction capability, which are characteristics of a good bioremediating candidate. They may help to protect humans from heavy metal toxicity by reducing soil metal accumulation and also reduce heavy metal absorbance of edible plants.
