Indigenous bacteria are very potent and useful in remediating hazardous pollutants specific to particular geographical locations. This work aimed to isolate two potent acid red dye decolorizing bacterial strains, namely Bacillus sp. strain UoMP1 and Citrobacter sp. strain UoMP2, from a textile effluent sample and aimed to optimize the conditions and explore the probable enzymatic involvement. The two isolates, namely D2 and D3, exhibited tolerance towards dye in an optimized concentration range of 2-4%. The decolourization percentage was approximately 80% for D2 and 75% for D3. The optimized conditions for decolourization were 72 h of incubation, pH 7, and a temperature of 37 °C. It is well known that the enzymes from the class reductase play a key role in the decolourization of various dyes and other xenobiotics. In this study, the azoreductase activity in D2 and D3 was found to be remarkably high under optimal conditions. The maximal intracellular azoreductase activity was 6.5 and 2.5 µg of acid dye reduced/min per mg of protein in D2 and D3 isolates, respectively. In the D2 isolate, an increased concentration of extracellular polysaccharides under dye stress suggested a possible role of extracellular decolourization and complexation mechanisms. Based on the 16 s RNA gene amplification, sequencing, and analysis, D2 and D3 were identified as Bacillus sp. strain UoMP1 and Citrobacter sp. strain UoMP2, respectively. Bacillus sp. strain UoMP1, an indigenous bacterial isolate, was found to be very efficient in decolourization of an azo dye-acid red dye used in the silk industry. This study provides valuable insights into the non-toxic tolerable dye concentration for these bacterial cells, which employ both enzyme-based decolourization mechanisms and extracellular mechanisms via extracellular polysaccharide production. Further exploration of biochemical and molecular mechanisms will help refine these isolates for field applications.

Department of Environmental Science Central University of Kerala Tejaswini Hills Tejaswini Hills Periye 671316 Kerala India

Department of Zoology College of Science King Saud University PO Box 2455 11451 Riyadh Saudi Arabia

Division of Biological Sciences School of Science and Technology University of Goroka Goroka 441 Papua New Guinea

Institute of Genomics for Crop Abiotic Stress Tolerance Department of Plant and Soil Science Texas Tech University Lubbock TX 79409 USA

Nanobiotechnology Laboratory Department of Studies in Biotechnology University of Mysore Manasagangotri Mysuru Karnataka 570006 India

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