Development of high concentration hexavalent chromium resistant strain of Aspergillus niger for improved Cr6+ biosorption : Scanning Electron Microscopic and spectrophotometric studies

Abstract

Hexavalent chromium (Cr 6+ ) is one of the most potent heavy metal pollutant released from various industries into water bodies. Most commonly used physico-chemical methods, for the removal of Cr 6+ from waste waters are inefficient, expensive and also produces unmanagable toxic sludge. Recent studies showed that biosorption, based on metal-biomass interaction can be an alternative to commonly employed methods for Cr 6+ removal from waste waters. Among the various biosorbent, bacteria, yeast, algae and fungi have potential for Cr 6+ biosorption. In this study, Bacillus circulans MTCC 3161, Saccharomyces cerevisiae and Aspergillus niger were screened for high Cr 6+ concentration tolerant strain isolation. It was found that, Bacillus circulans MTCC 3161 and Saccharomyces cerevisiae are resistant up to 800 ppm of initial Cr 6+ concentration present in the fermentation media, whereas, Aspergillus niger can resist up to 900 ppm of initial Cr 6+ concentration. Moreover, it was also found that Cr 6+ resistant Aspergillus niger have better biosorption potential (48% at 800 ppm) than that of Cr 6+ resistant Bacillus circulans MTCC 3161 and Saccharomyces cerevisiae (40% and 38% respectively at 800 ppm). Scanning Electron Microscopic studies of mycelia with spores of parent cells of Aspergillus niger, Cr 6+ resistant Aspergillus niger and Cr 6+ loaded Cr 6+ resistant Aspergillus niger revealed that exposure of parent Aspergillus niger to high Cr 6+ concentration induces morphological changes. Moreover, Cr 6+ loaded Cr 6+ resistant Aspergillus niger shows further changes in mycelial and hyphal morphology which occurs may be due to biosorption of Cr 6+ onto Cr 6+ resistant Aspergillus niger. Metal-biomass interaction was confirmed by Fourier Transform Infra Red (FTIR) spectroscopic study which also indicates the presence of hydroxyl, amine, amide, carbonyl or carboxyl groups, on cell wall of Aspergillus niger.