Plant growth promotion by a hexavalent chromium reducing bacterial strain, Cellulosimicrobiumcellulans KUCr3

This article reports on the isolation and characterization of a Cr(VI) resistant bacterial strain, having plant growth promoting properties to improve general growth of plant in chromium-contaminated soil through rhizosphere colonization. The strain was isolated from the sludge of waste canal carrying industrial effluents. The minimum inhibitory concentration of chromium to this strain was found to be 450 and 400 mM in complex and minimal media, respectively. The strain also showed varied degree of resistance to Cd, Co, As, Ni and Zn. It exhibited potential Cr(VI) reducing ability under aerobic culture conditions, and the factors affecting Cr(VI) reduction by this strain were evaluated. The optimum pH and temperature required to achieve maximum Cr(VI) reduction values were 7 and 35°C, respectively. Higher concentration of Cr(VI) slowed down the reduction, but with longer incubation time it reduced nearly all detectable amount of Cr(VI). The strain showed positive response to IAA production and phosphate solubilization. It promoted the growth of chilli plants in waste-fed soil with or without additional Cr through its establishment in rhizosphere. The successful establishment of KUCr3 in the rhizosphere of chilli plants helped to reduce Cr uptake by the test plant. This strain shows a promise that the multifarious role of this strain would be useful in the Cr-contaminated rhizosphere soil as a good bioremediation and plant growth promoting agent as well. Through biochemical characterization and 16S rDNA sequence analysis, the strain KUCr3, as the name given to it, was identified as a strain of Cellulosimicrobium cellulans.