Identification of keratinases from Fervidobacterium islandicum AW-1 using dynamic gene expression profiling

Keratin 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.