TEXTILE DYE BIOREMEDIATION POTENTIAL OF SOME RHIZOBIAL STRAINS AND THEIR HEAVY-METAL AND HIGH SALINITY TOLERANCE

Abstract

The discharge of untreated textile dye effluents enriched with toxic pollutants including dyes, heavy metals and other hazardous materials may cause negative impacts on the entire ecosystem. The proposed work aimed to isolate, molecularly identify and characterize the native rhizobial strains with textile dye biodegradation potential in relation with their tolerance to high salinity and heavy metals (usually meet in high concentrations in the textile dye effluents). Native rhizobial strains were isolated from various terrestrial ecosystems originated in Danube – Delta Biosphere Reserve. Most of the strains tolerated ≥ 2.0% NaCl. Our data showed that 3 strains (Agrobacterium sp.CR-B19; Rhizobium giardinii CR- B22 and Ensifer sp.CR-B26) were able to tolerate 15 ppm concentration of cadmium (Cd2+), whereas all strains identified as Rhizobium sp. (except R. leguminosarum CR-B10), and Agrobacterium sp. could tolerate 70 ppm of chromium (Cr6+).. Moreover, 3 indigenous strains (Rhizobium giardinii CR-B13; Rhizobium sp.CR-B15 and Agrobacterium sp. CR-B19) tolerated a concentration of 200 ppm of lead (Pb2+). In regard to azo-dye degrading potential, only Rhizobium leguminosarum CR-B10 was able to degrade the Reactive Orange 16 dye (90.18% decolorization) in stationary conditions, at 30°C. Comparatively, Agrobacterium sp. CR - B19 strain removed Reactive Orange 16 (sulphonic azo-dye) (78.92 % decolorization) and Reactive Blue 4 (antraquinonic dye) (12 % decolorization) by adsorbtion. Based on their bioremediation potential, the newly isolated rhizobial strains could be further used (in pure culture or in consortia) to develop a new environmental friendly and cost–effective biotechnology in order to reduce the toxicity of textile dyes effluents.