Biodegradation of waste chicken-feathers by an alkaline β-keratinase (Mukartinase) purified from a mutant Brevibacillus sp. strain AS-S10-II

Present study describes the improvement of alkaline β-keratinase production by ethyl methyl sulphonate (EMS)-induced mutant Brevibacillus sp. strain AS-S10-II and biodegradation of waste chicken-feather by a purified alkaline β-keratinase from this mutant strain. When compared with wild strain, the mutant strain (EMS-05) exhibited better growth rate, less generation time and significantly higher rate (p < 0.010) of alkaline β-keratinase production. Under scanning electron microscope, the EMS-05 strain displayed clear morphological variation. On the other hand, crude alkaline β-keratinase from wild-type and EMS-05 strains did not differ on biochemical parameters such as thermostability, detergent stability, Km and Vmax values toward keratin. A purified alkaline β-keratinase (Mukartinase MR) from EMS-05 strain displayed molecular weight of 55 kDa and presented Km and Vmax values toward keratin as 1.3 mg ml−1 and 19.8 μmol min−1 mg−1, respectively. Although activity optima were noted at pH 9.0–10.0 and at 37 °C, Mukartinase MR is a serine protease displaying activity over a broad range of pH (5.0–11.0) and temperature (25–55 °C). SEM study revealed Mukartinase MR could degrade 78%–82% of feather-keratin post 48 h of incubation. The quantity of amino acids released from the Mukartinase MR treated feather-keratin was detected in the following order: cysteine > valine > threonine > lysine > isoleucine > phenylalanine ≈ methionine. Release of at least seven volatile compounds from chicken-feather post treatment with Mukartinase was indicated by GC–MS and MALDI–TOF-MS analyses. The lack of toxicity of purified alkaline β-keratinase when tested on mammalian HT29 cells advocated its potential in industrial application on livestock feed formulation.

► A mutant Brevibacillus sp. showed higher rate of alkaline β-keratinase production as compared to wild-type strain.
► A purified alkaline β-keratinase (Mukartinase MR) from mutant strain showed optimum activity at pH 9.0–10.0 and at 37 °C.
► Mukartinase MR showed Km and Vmax values toward keratin as 1.3 mg ml−1 and 19.8 μmol min−1  mg−1, respectively.
► Mukartinase MR degraded 78% to 82 % of feather-keratin post 48 h of incubation and lack toxicity on mammalian cells.
► Present study suggests industrial application of this serine protease (Mukartinase MR) in livestock feed formulation.