Reduction of hexavalent chromium using fungi and bacteria isolated from contaminated soil and water samples

The reductive adsorption of hexavalent chromium (Cr6+) using six indigenous microorganisms isolated from contaminated soil and water samples was investigated. Quantification of Cr6+ reduction was determined using the 1,5-diphenylcarbazide method followed measuring the absorbance at OD540. Bacterial isolates identified as Klebsiella pneumoniae, Bacillus firmus and Mycobacterium sp. were capable of absorbing Cr6+ efficiently into their biomass, whereas the fungal isolates, Aspergillus flavus, Aspergillus sp. and A. niger were capable of transforming Cr6+ to Cr3+ relative to cell-wall-binding properties. Infrared spectral analysis of functional groups showed that ‒OH, ‒NH2 and C˭O with conjugated ‒NH were the binding groups responsible for adsorption of Cr6+ within the biomass of isolates. The data highlight the promising biotechnological application of these isolates in removing carcinogenic and mutagenic Cr6+ from contaminated ecosystems.