Cr(VI) toxicity inhibits microbe enhanced plant growth promotion without affecting bioremediation potential

Abstract

Hexavalent Chromium [Cr(VI)], a toxic inorganic pollutant of agriculture soil derived from various anthropogenic industrial sources, disturbs vegetation and contaminates the food chain. Chromate microbial toxicity was studied using plant growth-promoting chromate reducing Pseudomonas aeruginosa ATCC P15442 (P15). With a minimum inhibitory concentration of 1,250 µg/ml Cr(VI), the isolate is capable of 98% bioreduction of 100 µg/ml Cr(VI) in 24 hours and 83% of 500 µg/ml Cr(VI) in 72 hours. Additionally, P15 shows tolerance to cross heavy metal pollutants (Cd, Pb, and Zn), halotolerance, and the production of plant growth-promoting substance, such as indole acetic acid (IAA), siderophore, and phosphate solubilization in the presence and absence of Cr(VI). This study also reports that 100 and 250 µg/ml Cr(VI) decreases the production of IAA, siderophore, and phosphate solubilization without affecting the growth or Cr(VI) bioreduction ability. In Vigna mungo seed bacterization assay, P15 is capable of enhancing root and shoot length in absence of Cr(VI) and reversing toxic effects of 100 µg/ml Cr(VI). No enhancement of plant parameters was observed at higher Cr(VI) concentrations, except reversal of Cr toxicity. These data are indication of the detrimental effect of Cr(VI) pollution on rhizospheric microbial flora associated with plant growth-promoting activities.