Indole-3-acetic acid synthesizing chromium-resistant bacteria can mitigate chromium toxicity in Helianthus annuus L.

Abstract

Use of microorganisms as heavy metal remediators is an effective approach for chromium reduction in plants. Chromium carcinogenicity (Cr<sup>6+</sup>) beyond the permissible levels elicits environmental and health problems. To reduce chromium toxicity along with the plant growth improvement, a cost-effective and eco-friendly remediation approach is necessary. In the current study, chromium-resistant bacterial species were evaluated for growth improvement of sunflower. Three auxin-producing bacteria able to tolerate hexavalent chromium, i.e., Sporosarcina saromensis (EI) and two species of Bacillus cereus (AR and 3a) were selected for the proposed study. Growth studies along with auxin synthesis potential of bacterial isolates with and without chromium were conducted. Results revealed a 188% enhancement in plant height under laboratory-grown plants with B. cereus (AR) under 500 mg/L chromium stress (Cr<sup>6+</sup>). B. cereus (3a) also showed an 81% increase in leaf number with 400 mg/L chromium stress in laboratory-grown plants. Similarly, 73% increment in the amount of auxin was reported in the case of inoculation with S. saromensis isolate (EI) over respective control treatment. These improvements provide an excellent means of reducing chromium (Cr<sup>6+</sup>) in the contaminated soils naturally by stimulating plant growth along with bioremediation potential.