Effect of various conditions on stabilizing laccase activity in Bacillus subtilis spores and evaluating the ability of laccase to decolorize azo dyes

Abstract

Laccase is a polyphenol oxidase, and stabilizing its activity can be challenging. Therefore, developing a method to stabilize laccase activity is of practical significance. Bacillus subtilis was cultured to produce spores, and the time and method for collecting spores to achieve the highest laccase activity were investigated. Laccase activity from the B.subtilis sample increased 14.53 times after 04 days of culture compared to the first day. The biomass containing spores was treated with NaCl and CuSO4 to create samples with laccase activity. After treatment, the sample was preserved in CuSO4 to assess the stability of laccase. Among the CuSO4 concentrations tested, 0.25mM CuSO4 gave the highest laccase activity (39 U/g), which increased 2.38 times after 6 weeks of preservation. Regarding the effect of temperature, the sample preserved at 4oC showed the highest activity increase (29 times) and the most stability, compared to samples preserved at -4oC (1.19 times) and 37oC (2.02 times). As for preservative time, the sample preserved in 0.25mM CuSO4 at 4oC for 12 weeks retained laccase activity, with a 2.64 times increase (39.42 U/g). After 09 weeks, the laccase activity increased the most, showing a 3.44 times increase (51.33 U/g). The sample preserved in 0.25mM CuSO4 showed the % discoloration of 46.75%, 65.02%, and 70.89% after 04, 08, and 12 weeks, respectively. The results demonstrate a positive correlation between laccase activity and the Congo red decolorization ability of the spore sample.