Isolation, Molecular Identification, and Bioremediation Activity of Chromium-Resistant Bacteria Collected from Waste Waters in Leather Tanning Plants of Khuzestan, Iran

Environmental pollution with heavy metals is increasing with the development of the industry. The aim of the present study was to examine the isolation and molecular identification of chromium-resistant bacteria from contaminated wastewaters to investigate the bioremediation of chromium by them.

Chromium-resistant bacteria were isolated from tannery and leather factory effluents. The temperature, pH, BOD, COD, and the amount of heavy metals in each sample were determined. Bacterial isolation was performed by the agar dilution method in the presence of different concentrations of chromium from 1 to 128 mmolL-1. Then, the MIC and MBC for the selected strains were determined. The molecular identification of the resistant strains was done by colony PCR. The biological removal of chromium was evaluated by the selected strains under in vitro conditions.

The results of the study showed that the temperature, pH, BOD, and COD in the leather factory effluent were 28.7 ° C, 7.10, 100, and 330 mgL-1 and in the tannery effluent were 26.03 ° C, 6.84, 110, and 480 mgL-1, respectively. In this study, Bacillus subtilis H1F and Bacillus sp. H1D were isolated from leather wastewaters and Bacillus cereus H2C was the selected strain from tannery effluents. Among them, B. subtilis H1F showed the highest chromium resistance with an MIC value of 64 mM. Chromium removal of this strain was 68.5 ppm and it had the highest capacity among the three selected isolates.

Considering that B.subtilis H1F had the highest resistance and adsorption of chromium compared to other two bacteria, it is a suitable candidate for the biological removal of chromium from polluted effluents.