Chromium Reducing and Plant Growth Promoting Potential of Mesorhizobium Species under Chromium Stress

ABSTRACT

Chromium-reducing and plant growth–promoting potential, including production of siderophores by chromium(VI)-resistant Mesorhizobium species RC1 and RC4, isolated from chickpea nodules, was assessed both in the presence and absence of chromium(VI) under in vitro conditions. The Mesorhizobium strains displayed a high level of tolerance to chromium (400 μg ml^{− 1}), and showed a varied sensitivity to antibacterial drugs, on yeast extract mannitol (YEM) agar plates. Mesorhizobium strains RC1 and RC4 reduced chromium(VI) by 84% and 83%, respectively at pH 7 in YEM broth after 120 h of incubation. Mesorhizobial strains RC1 and RC4 produced 27 and 35 μg ml^{− 1} of indole acetic acid (IAA), respectively, in Luria-Bertani broth with 100 μg ml^{− 1} of tryptophan. The IAA production by the mesorhizobial strains did not differ significantly (p ≤ .05) under chromium stress and showed a positive reaction for siderophore, HCN, and ammonia, both in the absence and presence of chromium(VI).The present observations suggest that the chromium reducing and plant growth promoting activities of the Mesorhizobium strains could be exploited for bioremediation of chromium(VI) and to enhance the legume productivity for chromium-contaminated soils.

KEYWORDS:

• chromium tolerance
• chromium reduction
• Mesorhizobium
• plant growth-promoting activities

Notes

^a HCN = hydrogen cyanide

^b CAS = Chrome Azurol S agar

^c SA = salicylic acid

^d DHBA = dihydroxybenzoic acid

^e IAA = indole acetic acid

^f T = tryptophan concentration (μg ml^{− 1}); − = no production.