Abstract
SummaryKeratin degradation is of great interest for converting agro‐industrial waste into bioactive peptides and is directly relevant for understanding the pathogenesis of superficial infections caused by dermatophytes. However, the mechanism of this process remains unclear. Here, we obtained the complete genome sequence of a feather‐degrading, extremely thermophilic bacterium, Fervidobacterium islandicum AW‐1 and performed bioinformatics‐based functional annotation. Reverse transcription PCR revealed that 57 putative protease‐encoding genes were differentially expressed in substrate‐dependent manners. Consequently, 16 candidate genes were highly expressed under starvation conditions, when keratin degradation begun. Subsequently, the dynamic expression profiles of these 16 selected genes in response to feathers, as determined via quantitative real‐time PCR, suggested that they included four metalloproteases and two peptidases including an ATP‐dependent serine protease, all of which might act as key players in feather decomposition. Furthermore, in vitro keratinolytic assays supported the notion that recombinant enzymes enhanced the decomposition of feathers in the presence of cell extracts. Therefore, our genome‐based systematic and dynamic expression profiling demonstrated that these identified metalloproteases together with two additional peptidases might be primarily associated with the decomposition of native feathers, suggesting that keratin degradation can be achieved via non‐canonical catalysis of several membrane‐associated metalloproteases in cooperation with cytosolic proteases.
Highlights
The recent increase in the global consumption of poultry meat has resulted in the ongoing release of a vast amount of native feathers as an environmental solid waste during poultry processing
To complete the draft genome sequence of F. islandicum AW-1, which consisted of 12 contigs containing 2184 protein-coding genes (Lee et al, 2015b), we performed next-generation sequencing (NGS) using P6-C4
EggNOG platform analyses of the F. islandicum AW-1 genome revealed that 1695 of the identified genes could be classified into functional categories based on clusters of orthologous gens (COG) designation (Fig. S1)
Summary
The recent increase in the global consumption of poultry meat has resulted in the ongoing release of a vast amount of native feathers as an environmental solid waste during poultry processing. Crystalline feather keratin is comprised of densely packed b-pleated sheets that are further stabilized by numerous hydrogen bonds (Suzuki et al, 2006) and disulfide bond cross-links (Parry et al, 1977). Such insoluble and recalcitrant fibrous proteins (Ashby, 2004) are commonly incinerated, disposed of in landfills, or chemically hydrolysed, resulting in (i) generation of greenhouse gases in the course of waste treatment, concomitant with energy loss; (ii) loss of essential amino acids via acid hydrolysis; or (iii) poor digestibility in the animal gastrointestinal tract with some negative effects on the nutritional value of animal feeds.
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