Abstract
Millions of tons of feathers produced annually by the poultry industry cause environmental pollution and waste a significant source of protein. In the present study, three keratinolytic Bacillus strains, Bacillus sp. MK1, MK2, and MK3 were isolated. Some of the enzymatic properties of these keratinases were determined. The effects of some chemicals on enzyme activities were investigated. The specific activities of MK1, MK2, and MK3 were 2.76, 0.77, and 5.48 U/mg protein at 40°C, respectively, and mutant varieties were overexpressed after EtBr treatment. A comparison of keratinase activity between native and improved isolates showed that mutant variants exhibited higher activity ranging from 116 to 214%. According to BLAST analysis, the Bacillus sp. MK1 rDNA sequence was 96.83% similar to that of B. subtilis subsp. stercoris strain 153, B. subtilis strain FR10, B. tequilensis strain P12, and B. subtilis strain SRR21, and Bacillus sp. MK2 and MK3 16S rDNA sequences were 99.54% similar to those of B. subtilis strain 21M and B. subtilis strain NX17 sequences. The results of the enzymatic analysis of the enzymes and overexpressed mutant varieties are promising for application in the industrial production and application of the enzymes decomposition of feathers in poultry sector.
Highlights
Keratin is an insoluble fibrous protein and the main component in feathers (Jeong et al 2010), hair, wool, nails, horns (Onifade et al 1998), vertebrate skin, hooves, and scales (Feughelman 1985)
The mixture was allowed to settle at room temperature for 10 min, after which 0.5 mL soil supernatant was transferred into a sterile microcentrifuge tube and incubated at 80°C for 10 min to destroy any vegetative bacteria
Three keratinolytic bacteria were isolated and identified as Bacillus because they germinated from spores under aerobic conditions (Remize 2017) and from the results of the API 20E test
Summary
Keratin is an insoluble fibrous protein and the main component in feathers (Jeong et al 2010), hair, wool, nails, horns (Onifade et al 1998), vertebrate skin (epidermis), hooves, and scales (Feughelman 1985). Feathers are made of pure β-keratins (Wakil et al 2011) that are highly insoluble and difficult to decompose (Agrahari & Neeraj 2010). The poultry industry produces 8–8.5 Gt of feathers annually (Manju 2012, Sah et al 2015), which are used as landfill by either burning or burying. These processes cause problems with storage transportation, disposal of ashes, and greenhouse-gas emissions (Khodayari & Kafilzadeh 2018). 90% of the weight in feathers is made up of keratin, which does not decompose (Mousavi et al 2013); it is an abundant and inexpensive source of protein
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