Biodegradation of different keratin waste by newly isolated thermophilic Brevibacillus gelatini LD5: Insights into the degradation mechanism based on genomic analysis and keratin structural changes

Keratin is an abundant environmental solid waste. This work isolated a thermophilic strain from a hot spring with efficient keratinolytic ability. The strain was identified and named as Brevibacillus gelatini LD5 based on whole-genome sequence analysis. The strain has genes related to keratin degradation, including disulfide reduction, keratin denaturation, protein proteolysis and metabolism of amino acids. The keratinases derived from this strain were the endo-acting M4, M16 and S8 proteases, exo-acting S9 protease and oligo-acting M3 and M32 peptidases via Conserved Unique Peptide Patterns (CUPP) prediction. The LD5 can degrade different keratin biomass, e.g. chicken feathers (CF), goose feathers (GF), pig hair (PH), cat hair (CH) and dog hair (DH). The degradation rate of CF was 62.45 % after 24-h fermentation. The hydrolysates from different keratin biomass have all shown keratinolytic activity, antioxidant and antiradical activities. The random structure of keratin was easier to be degraded by LD5 from Fourier transform infrared (FT-IR) analysis. The optimum temperature-pH conditions of the keratinases were 79.8 °C and pH 7.5, and thermal stability of the keratinases reached 71.5 min at 70 °C. These results demonstrated that B. gelatini LD5 has potential application in keratin wastes biodegradation and thermal stable keratinase production.