Compound mutation by ultraviolet and diethyl sulfate of protease producing thermophilic bacteria to hydrolyze excess sludge

•A genetically stable mutant strain KT16 was screened by UV-DES compound mutagenesis.•The enzyme activity of KT16 increased by 46.7% compared to the original strain DC8.•Mutagenesis enhanced the ability of S-TE, facilitated the recovery of protein in ES.•Whole genome resequencing analysis of KT16 was performed to detect the mutant sites. Excess sludge (ES), a resource-rich organic waste, can be solubilized by thermophilic enzymes to extract proteins for sludge reduction and resources recovery. To solve the problems of low hydrolysis effect of ES and low enzyme producing ability of wild thermophilic bacteria, ultraviolet and diethyl sulfate (UV-DES) were adopted to mutate thermophilic bacteria in this study. Mutation sites were detected and annotated by whole genome sequencing analysis. The results showed that UV-DES mutagenesis could effectively improve enzyme-producing capacity of thermophilic bacteria and promote the hydrolysis of ES. The protease activity of the mutant strain KT16 was 46.7 % higher than that of the original strain DC8. The protein extraction rate with enzyme produced by KT16 reached 83.3 %. The total content of proteins recycled through KT16 enzyme solution was 3539.6 mg·L-1, 18.4 % higher than that of DC8. This work provided a theoretical idea and technical guidance for the protein recovery from ES.