Recombinant expression and molecular engineering of the keratinase from Brevibacillus parabrevis for dehairing performance

Keratinase is capable of distinctive degradation of keratin, which provides an eco-friendly approach for keratin waste management towards sustainable development. In this study, the recombinant keratinase (KERBP) from Brevibacillus parabrevis was successfully expressed in Escherichia coli. The purified KERBP had the specific activity of 6005.3 U/mg. It showed remarkable tolerance to various surfactants and also no collagenolytic activity. However, the moderate thermal stability limited its further application. Thus, protein engineering was further adopted to improve its stability. The variants of T218S, S236C and N181D were constructed by site-directed mutagenesis and combinatorial mutagenesis. Compared with the wild type, the t_1/2 at 60 °C for the variants T218S, S236C and N181D were 3.05-, 1.18- and 1-fold increase, respectively. Moreover, the double variants N181D-T218S and N181D-S236C significantly improved thermostability with 5.1 and 2.9 °C increase of T₅₀, and prolonging t_1/2 at 60 °C with 4.09 and 1.54-fold, respectively. And the catalytic efficiency of the T218S and N181D-T218S variants was also significantly improved. Furthermore, the keratinase displayed favorable ability to dehair wool from skin within 7 h, which showed potential in leather dehairing. Our work contributes to a further insight into the thermostability of keratinase and offers a promising alternative for industrial leather application.

Chitin extraction from shrimp waste by liquid fermentation using an alkaline protease-producing strain, Brevibacillus parabrevis

In this study, an extracellular protease, but no chitinolytic enzyme-producing strain, Brevibacillus parabrevis TKU046, has been isolated and analyzed for the deproteinization testing of shrimp waste by liquid fermentation. Deproteinization assays of shrimp waste with this microbe showed 95% protein removal after 4 days fermentation. The efficiency of chitin extraction by B. parabrevis TKU046 on wastes of three shrimp species were also investigated in which the highest deproteinization was found on cooked tiger shrimp shell. Infrared spectra (IR) of the obtained chitin displayed characteristic profiles for chitin. The culture supernatant released after fermentation greatly exhibited growth enhancing effect on Lactobacillus rhamnosus. In addition, B. parabrevis TKU046 protease was isolated and determined the characteristics. The molecular mass of B. parabrevis TKU046 protease was determined as 32 kDa and 34 kDa, respectively, by SDS-PAGE and HPLC. Overall, the findings provide strong support for the potential candidacy of this enzyme as an effective and eco-friendly alternative to the conventional chemicals used for the deproteinization of shrimp heads in the chitin processing industry, as well as the production of prebiotics to be used in the nutraceutical industry.

Screening of a beta-cypermethrin-degrading bacterial strain Brevibacillus parabrevis BCP-09 and its biochemical degradation pathway

A novel beta-cypermethrin (Beta-CP)-degrading strain isolated from activated sludge was identified as Brevibacillus parabrevis BCP-09 based on its morphological and physio-biochemical characteristics, and 16S rRNA gene analysis. Strain BCP-09 could effectively degrade Beta-CP at pH 5.0-9.0, 20-40 °C, and 10-500 mg L^-1 Beta-CP. Under optimal conditions (pH 7.41, 38.9 °C, 30.9 mg L^-1 Beta-CP), 75.87% Beta-CP was degraded within 3 days. Beta-CP degradation (half-life, 33.45 h) and strain BCP-09 growth were respectively described using first-order-kinetic and logistic-kinetic models. Seven metabolites were detected by high-performance liquid chromatography and gas chromatography-mass spectrometry- methyl salicylate, catechol, phthalic acid, salicylic acid, 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid, 3-phenoxybenzaldehyde, and 3-phenoxybenzoic acid (3-PBA). The major Beta-CP metabolite, 3-PBA was further degraded into phenol, benzoic acid, and 4-methylhexanoic acid. BCP-09 also degraded aromatic compounds such as phenol, catechol, and protocatechuic acid. Beta-CP appears to be mainly degraded into 3-PBA, which is continuously degraded into smaller benzene or chain compounds. Thus, strain BCP-09 could form a complete degradation system for Beta-CP and might be considered a promising strain for application in the bioremediation of environments and agricultural products polluted by Beta-CP.

Biochemical characterization of a novel surfactant-stable serine keratinase with no collagenase activity from Brevibacillus parabrevis CGMCC 10798

Dehairing is a high pollution process in leather industry. Conventionally, the lime-sulfide mediated chemical process for dehairing would lead to the discharge of pollutants and corrosion of industrial equipment. Concerning these problems, keratinase has become a promising candidate for dehairing process in recent years. In this study, a keratinase-producing bacterium was isolated from sheepfold soil and identified as Brevibacillus parabrevis CGMCC 10798 based on the biochemical characteristics and molecular identification. The keratinase was purified to electrophoretic homogeneity with 17.19% of recovery, 13.18 folds of purification and an estimated molecular weight of 28kDa. The enzyme exhibited high keratinase activity and no collagenase activity. Besides, the keratinase showed optimal activity at 60°C and pH 8.0. The enzyme activity could be significantly increased in the presence of Na⁺ and Ca²⁺. And it was inhibited by EDTA, and PMSF, which indicated that the keratinase belongs to serine-metallo protease. The enzyme could remain stable in the presence of surfactants. Especially, 5mM Tween 40 and Triton 100 could improve the activity by 11% and 30%, respectively. Moreover, B. parabrevis keratinase could completely dehair goat wool within 7h, which indicated its application potential in leather industry.