Characterization and genomic analysis of a novel keratinolytic Streptomyces sp. 3–6 for efficient bioconversion of feather waste

The annual accumulation of vast quantities of poultry feather waste poses a significant global challenge to environmental sustainability and resource management. Feathers are protein-rich biomaterials; however, their highly recalcitrant β-keratin structure, stabilized by abundant disulfide bonds, renders them extremely resistant to degradation by conventional biological methods. This inherent recalcitrance contributes to persistent environmental hazards and represents a substantial loss of a potentially valuable biological resource. A novel feather-degrading actinobacterial strain was isolated from soil samples collected at a sea duck farm and identified as Streptomyces sp. 3–6 through integrated morphological, physiological-biochemical and genomic analyses. Optimum fermentation conditions were systematically determined using single factor experiments, Plackett-Burman (PB) screening, and orthogonal optimization, yielding the following parameters: feather, 25.0 g/L; yeast extract, 12.0 g/L; sucrose, 20.0 g/L; MgCl 2 , 4.0 g/L; initial pH, 10.0; and temperature, 30 °C. Under these conditions, strain 3–6 achieved near-complete feather degradation (~90% weight loss) within 120 h, with a maximum keratinase activity of 332.40 ± 11.25 U/mL, 2.64-fold higher than that observed in the basal medium (125.91 U/mL). The crude keratinase exhibited maximal activity at 70 °C and pH 7.0, and demonstrated remarkable pH stability across a broad range (pH 6.0–9.5). Amino acid analysis revealed that the fermentation hydrolysate was enriched in free amino acids, particularly nutritionally essential histidine and leucine. Genome-wide analysis identified sprD , a putative gene predicted to encode a canonical S1-family serine protease, underscoring the strain’s intrinsic genetic capacity for keratinolysis. The novel feather‑degrading actinobacterium Streptomyces sp. 3‑6, isolated from sea duck farm soil and exhibiting robust metabolic adaptability, employs a synergistic enzymatic system comprising keratinase and disulfide reductase to efficiently hydrolyze recalcitrant feather keratin into bioavailable amino acids. This capability positions the strain as a promising biocatalyst for the sustainable valorization of keratinous waste into high-value, protein-rich feed supplements.