Keratinolytic activity of Stenotrophomonas rhizophila and Bacillus spp. as keratin waste biodegradation

Document Type : Original article

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Department of Pathobiology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran

10.22099/mbrc.2026.55909.2288

Abstract

Waste feathers pose a significant environmental challenge due to their resistance and the large amounts produced by the poultry industry. In this study, we isolated and characterized a novel keratinolytic strain, Stenotrophomonas rhizophila SMT, from horse feces and evaluated its feather-degrading ability and production of soluble keratin hydrolysates. Additionally, its keratinolytic ability was assessed along with both Bacillus subtilis and Bacillus cereus. S. rhizophila SMT was identified by biochemical profiling and confirmed by 16S rRNA gene sequencing, which showed 99% similarity to S. rhizophila. Primary screening on skim-milk agar and egg-yolk agar showed their keratinolytic activity. Subsequent cultivation in minimal salt media with chicken feathers confirmed and quantified their feather degradation efficiency by using the Bradford assay. After 13 days, S. rhizophila SMT produced 0.535 mg/mL soluble protein, while B. subtilis and B. cereus produced 0.615 mg/mL and 1.215 mg/mL, respectively. S. rhizophila SMT is a safe and non-pathogenic candidate despite producing less soluble protein than B. cereus. This makes it an eco-friendly choice for management of feather wastes, especially when biosafety is a priority.

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