Uptake of toxic Cr (VI) by biomass of exo- polysaccharides producing bacterial strains

Abstract

Chromium (VI) is a toxic heavy metal, carcinogen and environmental pollutant. Microorganisms and the microbial products, however, possess the ability to remove it efficiently from the environment especially the dilute external solutions. Both the dead microbial biomass and the microbes are considered as an alternate tool to the conventional costly chemical techniques used for removal of the toxic metal from the polluted water bodies. The uptake of Cr (VI) from aqueous solution by living as well as dead biomass of three exo-polysaccharide producing bacterial strains, Bacillus cereus, Bacillus pumilis and Pantoea agglomerans, was studied under variable conditions of pH, temperature, metal concentration, biomass and contact time. Metal uptake showed a pH-dependent profile with optimum at pH values 2.0 for B. cereus and B. pumilis and 3.0 forP. agglomerans. The incubation experiments carried out at four different temperatures, 4, 25, 37 and 45°C exhibited the best uptake of the metal at 37°C. An increased solution concentration of the metal ion was inhibitory for its uptake. The uptake of Cr (VI) from the solution was rapid and most of it completed within first 15 min of incubation. At the initial Cr (VI) concentration of 50 µg ml-1, Cr (VI) uptake was 86.79, 87.79 and 83.64% by living biomass of B. cereus, B. pumilis and P. agglomerans and 89.87, 89.23 and 85.5% by dead biomass, respectively. Experimental results also showed the influence of the biomass concentration on the metal uptake for all the strains. Uptake by the dead biomass was slightly higher than the living cells of all the bacterial strains. It was concluded that the bacterial strains can be used for removal of chromium from polluted water. Key words: Chromium VI (Cr [VI]) uptake, Bacillus cereus, Bacillus pumilis, Pantoeaagglomerans