Bioremediation of textile dyes and improvement of plant growth by marine bacteria

Abstract: Textile industries are the major users of dyes in the world. A huge fraction of dyes are discharged out from the textile industries, causing serious damage to the environment. Bioremediation based technologies has been proved to be the most desirable and cost- effective method to counter textile dye pollution. The ability of the microorganisms to decolorize and metabolize dyes can be employed to treat the environment polluted by textile dyes. In this work, a total of 84 bacterial strains were isolated from Kelambakkam Solar Salt Crystallizer ponds (or salterns) and screened for their ability to produce extracellular tannase and laccase enzymes and eventually to decolorize three widely used textile dyes- Reactive Blue 81, Reactive Red 111 and Reactive Yellow 44. Of these 84 strains, 18 strains exhibited tannase activity and 36 strains showed positive laccase enzyme activity. The 11 bacterial strains that displayed both tannase and laccase enzyme activity were screened for their ability to decolorize the three textile azo dyes (100 mg/L). Out of 11 strains only 2 strains i.e., AMETH72 and AMETH77 showed best decolorization (%) in all the three dyes under static condition at room temperature. Repeated- batch immobilization study used to select the most efficient bacterial strain revealed that, isolate AMETH72 was efficient than AMETH77 in decolorizing the dyes. The 16S rRNA sequencing of AMETH72 showed 99% phylogenetic similarity to Halomonas elongata. The dye degradation products analyzed by FTIR and UV-Vis techniques displayed complete disruption of azo linkages and biodegradation of dyes to simpler compounds. The treated dyes also improved growth and total chlorophyll content in Wheat and Green gram seedlings, as compared to the untreated dyes. This indicated the non- toxicity of the biologically degraded dye products. Thus the entire study concluded that halotolerant marine bacteria from the salterns can be effectively used to bioremediate the textile dyes.