Unveiling the keratinolytic transcriptome of the black carpet beetle (Attagenus unicolor) for sustainable poultry feather recycling.

The black carpet beetle (BCB) is a household pest unique in its ability to digest complex proteins such as keratin that makes up the majority of feather structure. Despite voluminous yield and high protein content ( > 85%), feathers are poorly digested by most known organisms and are thereby rendered an environmental hazard. Furthermore, keratinolytic microbial strains are typically thermophilic and therefore economically and environmentally unsustainable. Given the BCB's ability to digest wool, feathers, and other keratin-rich materials, we assembled a de novo transcriptome of larvae fed on either feathers or standard chow. All proteolytic enzymes were identified via homology to the MEROPS database and subsequently annotated for a complete overview of enzymatic activity and distribution of peptidase clans in the transcriptome. Both differential expression and sequence homology screening were then used to identify potentially keratinolytic candidates from the assembly to be used in future expression experiments. The BCB transcriptome showed a high proportion of serine (22.6%) and cysteine (18.9%) proteases as well as metallopeptidases (25.5%) compared with other insect species. Regarding differential expression, serine and metalloproteases represented a large proportion of upregulated genes in the feather-fed group, constituting 42.9% and 57.1% of upregulated proteases, respectively. Additionally, several candidate transcripts identified through homology screening showed significant sequence overlap to seven existing keratinases, indicating a strong likelihood of keratinolytic function in this organism. KEY POINTS: • A de novo transcriptome of black carpet beetle larvae was assembled. • The transcriptome consisted of 67% of serine, cysteine, and metalloproteases. • Differential transcriptomes of beetles fed feather and chow were compared.