Beyond keratinases: Oxidoreductase-Mediated Pathways Underlying Feather Degradation Mechanism by Streptomyces sp. G11C

Background. Feather waste is an abundant keratin-rich byproduct generated by the poultry industry that represents an important environmental challenge due to the recalcitrant nature of keratin. Although keratinolytic microorganisms have emerged as promising biotechnological tools for feather valorization, the molecular mechanisms underlying bacterial keratin degradation remain poorly understood. In this study, we investigated the protein machinery involved in keratin degradation by Streptomyces sp. G11C using a global label-free shotgun proteomic approach. Results. Proteomic analysis of cellular and extracellular fractions collected after 3 and 5 days of cultivation identified 794 proteins, with proteases and oxidoreductases among the most abundant functional groups. An S8 serine protease and an M6 metalloprotease were identified as the major candidate keratinases, and their roles were experimentally validated through overexpression in Streptomyces sp. G11C, resulting in approximately 2.5-fold higher keratinolytic activity than the wild-type strain. Additional components, including lytic polysaccharide monooxygenases and dihydrolipoyl dehydrogenases, highlight oxidoreductase-mediated mechanisms for keratin denaturation and disulfide bond reduction, suggesting a previously unrecognized contribution to bacterial keratin degradation. Sulfite production was detected during feather degradation, although its relatively low concentration supports a predominant role for enzymatic disulfide reduction. In addition, proteins involved in sulfur metabolism, oxidative stress response, protein folding, and cellular adaptation, including γ-glutamyl transferase, catalases, DnaK, and TerD proteins, were identified, indicating coordinated physiological responses during keratin utilization. Conclusions. Our findings support a multistep model of bacterial keratin degradation in which oxidoreductase-mediated destabilization of the keratin structure precedes extracellular proteolysis and is accompanied by metabolic and stress-adaptation processes. This work provides new mechanistic insights into microbial keratin degradation, identifies novel enzymes potentially involved in this process, and expands the current understanding of bacterial keratin utilization, offering new opportunities for the development of sustainable biotechnological processes for feather waste valorization.