IAA production by Bacillus sp. JH 2-2 promotes Indian mustard growth in the presence of hexavalent chromium

Bacillus sp. strain JH 2-2, isolated from the rhizosphere of plants at a multi-metal contaminated mine site, has the potential to reduce Cr(VI) to Cr(III) and promote plant growth by reducing Cr toxicity and producing IAA. The minimum inhibitory concentration of Cr(VI) to Bacillus sp. JH 2-2 was 1000mgL^-1 and the strain reduced 99% of 10mg Cr(VI)L^-1 to Cr(IV) within 24h. Lower Cr(VI) stress (10mgL^-1) stimulated IAA production, but much less IAA was produced at 30 or 50mg Cr(VI) L^-1. Inoculation with Bacillus sp. JH 2-2 increased the length of Brassica juncea L. roots by 364% and stems by 735% in the presence of 10mg Cr(VI)L^-1 from those of uninoculated control plants. These findings suggest potential use of Bacillus sp. JH 2-2 to promote phytoremediation of soil contaminated with Cr(VI).