Abstract

The main objective of the present research is to identify and characterize the essential genes responsible for Cr removal by the highly resistant bacterial strain Pseudomonas stutzeri Strain M15-10-3 isolated from leather tanning industrial wastewater to optimize its capacity and to be exploited in the development of chromium bioaccumulation capacity in other microorganisms. Pseudomonas stutzeri (PS) was previously investigated among a total of 20 bacterial isolates (17 indigenous and 3 exogenous) to decontaminate heavily polluted leather tannery wastewater using batch and fixed (biofilm) mode where it exhibited remarkable efficiency in removing Cr, the highly toxic and main contaminant in tannery effluent. PS and 3 sub strains of Bacillus cereus ATCC 14579 were subjected to 4 elevated Cr levels (2000-5000 mg/l) for 9 days to confirm the PS affinity for Cr bioaccumulation. Results proved the highest affinity of PS (≈ 80%) to bioaccumulate Cr from polluted media even at very high concentration (5000 mg/l). Moreover, Cr has remarkable inhibition activity on the growth of Bacillus cereus strains (75 to 99.7%) even at the lowest tested Cr concentration without any stimulation at all the tested concentrations. However, PS exhibited the superior acclimatization ability against Cr even at the highest Cr concentration reflecting its high Cr resistance with 25% growth stimulation at 4000 mg Cr/l and the lowest growth inhibition (37.1% at 2000 mg Cr/l). Therefore, PS was considered highly efficient candidate for Cr removal and was selected to be molecularly investigated to characterize Cr resistance genes. Results demonstrated that ChrT gene responsible for chromate reduction ability was most probably present in Pseudomonas stutzeri genome.