Biodegradation and phytotoxicity evaluation of textile azo dye effluent using alkaline protease enzyme from halophilic bacterium Halobacillus trueperi RRJS1

Abstract

Halophiles are salt loving bacteria and they are capable of producing extracellular enzymes. Nowadays, these enzymes are utilized as one of the main ingredients by the industries for manufacturing products and some environmental researchers exploit it for biodegradation studies. The present study highlights the unique biodegradation potential of Halobacillus trueperi RRJS1, a halophilic bacterium capable of producing highly active alkaline protease enzyme. It can withstand high salinity and can survive osmotic stress in the extreme salt concentration. Generally, halophiles produce more extracellular enzymes in high salt concentrations which are generally called as halozymes. Halophiles are salt loving bacteria that thrive in salt lakes and they are competent to produce more extracellular enzymes. These enzymes remain stable under these conditions. In the present research, the halophilic bacteria H. trueperi RRJS1 is screened for production of alkaline protease enzyme and it was used for the degradation of highly toxic ingredients found in the textile azo dye effluent. The bacterial strain H. trueperi RRJS1 was optimized with various physico - chemical parameters and maximum production of the alkaline protease enzyme was recorded at 40 °C and pH 7.5 (99.23 ± 0.42 U/ml); and in 6 % NaCl concentration (60.5 ± 1.28 U/ml). Among the nutritional sources, 1 % lactose and 1 % beef extract were induced maximum production of alkaline protease (24.7 ± 0.8 U/ml and 59.1 ± 0.56 U/ml). The physico-chemical parameters such as pH, BOD, COD, TDS, total hardness and chlorides were efficiently checked in the alkaline protease enzyme treated textile azo dye effluent. Degradation of textile azo-dye effluent by alkaline protease enzyme was conducted and highest percentage of degradation (84.30 %) was observed at alkaline protease enzyme produced by lactose. The GC-MS analysis of the alkaline protease treated textile azo dye effluent exhibited the presence of major and minor chemical compounds, and they were responsible for the degradation of azo dye components and 100 % disappearance of compounds in raw textile azo dye effluent was observed. The phytotoxicity studies on black gram Vigna mungo revealed that the plants grown on the alkaline protease treated textile azo dye effluent enhanced seed germination (80 %), plumule (8.7 ± 1.35 cm) and radicle length (3.5 ± 1.80 cm) and less growth were observed in the raw textile azo dye effluent treated plants. The textile azo-dye effluent often encompassed with high concentration of salt and it could inhibit growth of the most microbial organisms in the polluted textile water. But, in this study, the extracellular protease enzyme from the halophilic bacteria H. truperi RRJS1 exhibited reliable performance for the degradation of textile azo-dye effluent. This eco-friendly strain could effectively support sustainable textile waste water treatment strategies and remove the contaminants in the highly polluted textile azo-dye effluent.