Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/17221
Title: Chromium Toxicity and Bioaccumulation by Chromium - Tolerant Bacillus and Arthrobacter Species
Authors: SHAILENDRA MISHRA
Keywords: Bioaccumulation, chromium toxicity, Bacillus, Arthrobacter, SEM, TEM
Issue Date: 15-Dec-2009
Source: SHAILENDRA MISHRA (2009-12-15). Chromium Toxicity and Bioaccumulation by Chromium - Tolerant Bacillus and Arthrobacter Species. ScholarBank@NUS Repository.
Abstract: Rapid industrialization has given rise to high level of heavy-metal pollution which is a major environmental concern due to the toxic effects of these metals; their accumulation up the food chain gives rise to serious ecological and health implications. Hexavalent chromium (Cr) is one such metal that is well-known for its high toxicity and is hence considered a priority pollutant. This study has investigated chromium removal capacity from synthetic effluent by chromium resistant microorganisms isolated from a contaminated site with chromium. The two isolates were found to be novel species. The nearest homologs and phylogentic tree derived through 16S rDNA analysis showed only 98% and 96% similarity to Bacillus sp. and Arthrobacter sp. respectively. These organisms were tested for their adaptability towards chromium by increasing the concentration of chromium in M1 culture media. In other words, enrichment of the isolates was performed in order to test the toxicity effect of chromium on these isolates during logarithmic growth phase. Arthrobacter sp. adapted faster when compared to Bacillus sp. The characterization of the exo-polysaccharides showed that Arthrobacter sp. was more tolerant towards chromium when compared to Bacillus. It was found that both the isolates were able to remove more than 50% of chromium in 3-5 hours and more than 95% in 24 hours at a range from 2 ppm to 40 ppm of chromium. When the removal capacity was compared, it was found that Bacillus sp. was able to sequester more chromium than Arthrobacter sp. The intracellular compartmentalization of chromium by the two isolates showed that Bacillus sp. could intracellularly uptake more chromium than Arthrobacter sp. FTIR studies indicated that the main adsorption sites for chromium are the amino and carboxylate group. XRD analysis showed that chromium was associated with phosphoryl, hydroxyl, carboxyl and carbonyl attachment. XPS analysis represented the speciation of the chromium adsorbed by the cells. It was found that the intensity of the peaks were higher in the case of Bacillus sp. than Arthrobacter sp., indicating higher adsorption. AFM analysis showed that Arthrobacter sp. is more tolerant towards chromium by the production of Exopolysaccharides. SEM analysis showed the formation of cage like structure in the case of Bacillus sp. that increases the capacity of the metal to bind to the cells. It also shows the agglomeration of cells due to large production of EPS in the case of Arthrobacter sp.. EDX analysis showed the replacement of cations (sodium and potassium) by chromium. TEM analysis further presents evidence of chromium accumulation in the isolates. Bioaccumulation of chromium by the isolated was quantified using TEM coupled with EDX analyses.
URI: http://scholarbank.nus.edu.sg/handle/10635/17221
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