Pilot-scale inoculum-free valorization of raw chicken feathers: ammonium recovery, keratinase production and...

Chicken feathers constitute a major keratin-rich agro-industrial residue whose sustainable valorization remains challenging due to the recalcitrant structure of keratin and the energy-intensive nature of conventional treatments. In this study, we investigated the feasibility of converting raw, mechanically untreated chicken feathers into soluble nitrogen compounds and extracellular keratinases through an inoculum-free microbial process operated at pilot scale. A 50 L horizontal bioreactor was run using only tap water and the indigenous feather-associated microbiota, without sterilization, nutrient supplementation or pretreatment, under alternating aerated and oxygen-limited regimes. Substantial feather degradation was achieved, accompanied by the accumulation of ammonium in the liquid phase up to 5 g L⁻¹ and keratinase activities exceeding 31,000 U mL⁻¹, particularly under oxygen-limited conditions. High-throughput 16 S rRNA gene sequencing revealed a compact but resilient core microbiota whose temporal succession correlated with process performance. Dominance shifts among Comamonas, Wolinella, Tissierella and Pseudoxanthomonas suggested functional complementarity between taxa involved in keratin hydrolysis, peptide fermentation and nitrogen mineralization. The progressive enrichment of anaerobic or facultative anaerobic members during oxygen limitation was associated with intensified ammonium release and sustained enzymatic activity. Overall, this work demonstrates that native feather-associated microbial consortia can self-organize into a functionally stable community capable of driving keratin depolymerization and nitrogen recovery in the absence of an external inoculum. These findings highlight the biotechnological potential of starter-free microbial systems for low-input valorization of keratinous wastes and contribute to a deeper understanding of community-level processes underpinning industrially relevant bioconversions.