Simultaneous removal of reactive dyes and hexavalent chromium by a metal tolerant pseudomonas sp. WS-D/183 harboring plant growth promoting traits

Textile industry is a continuous source of colored wastewater. This wastewater frequently used for irrigation purpose in many underdeveloped countries including Pakistan. In this study, we isolated the bacterial strains capable of decolorizing dyes and promote the plant growth. Hence to decolorize the reactive red 120 (RR120), the strain WS-D/183 was optimized following response surface methodology (RSM) based modeling approach. Moreover, strain WS-D/183 was also assessed for plant growth promoting characteristics. Results revealed that the strain WS-D/183 showed a good potential for decolorization of structurally diverse types of azo dyes on reaction with a mixture of heavy metal ions (Cr⁶⁺, Cd²⁺, Zn²⁺, Pb²⁺). This strain concurrently removed reactive dyes (100 mg L^-1) and reduced Cr(VI). Results showed that each dye was decolorized up to 90% except reactive yellow-2 which was decolorized up to 57.4%. Furthermore, the bacterium reduced Cr(VI) by 41 to 95% along with concurrent decolorization of RR120. This bacterium was also found to carry plant growth promoting traits including inorganic phosphate solubilization (497.6 ± 14.8 μg mL^-1) and indole-3-acetic acid production (21.07 ± 0.9 pg mL^-1). A phytotoxicity evaluation study indicated that irrigation of mung bean [Vigna radiata (L.) Wilczek] with RR120, Cr(VI) and RR120+Cr(VI) contaminated waters treated with the strain WS-D/183 enhanced germination along with plumule and radical length of seedlings. Results suggested that Pseudomonas sp. WS-D/183 is a valuable addition to the bioresources, which can be used to devise textile wastewater treatment strategies as well as for integrated bioremediation and plant growth promotion in agricultural soils contaminated with textile wastewaters.