Evaluation of bacteria isolated from textile wastewater and rhizosphere to simultaneously degrade azo dyes and promote plant growth

BACKGROUND The release of untreated textile effluent to the environment and its subsequent application to cropland poses a serious threat to human health. Various bacterial species contained in the effluent can degrade azo dyes; however, no work has been done to elucidate the role of these bacteria for plant growth promotion (PGP). This study was designed to isolate and evaluate bacterial strains carrying dual traits for azo dye degradation and PGP. RESULTS About 468 bacterial isolates were collected from textile effluent, sludge and dye-contaminated soil through enrichment in mineral salt medium (MSM) containing reactive black-5 dye (100 mg L-1). Seven isolates (I-15, S-10, 7.3, 11.4, AE-5, AE-7 and AE-8) with promising potential to treat the dye (100% color removal in 12-24 h) also exhibited significant production of indole acetic acid (9-21 ?g mL-1) and halo ring formation (diameter 6-11 mm), which is indicative of phosphate solubilization (P-solubilization). Inoculation of the isolates to maize (Zea mays) plants grown in water and MSM containing the dye resulted in decolorization of the dye while significantly improving plant biomass compared with the control plants. CONCLUSIONS Our findings show that bacterial isolates possessing dual traits could be used simultaneously for textile effluent treatment and PGP.