The strain Chryseobacterium sp. kr6 shown to be useful for biotechnological purposes such as hydrolysis of poultry feathers and de-hairing of bovine pelts. The effect of temperature, initial pH and media composition on protease production by this keratinolytic strain was studied. The enzyme was produced between 25 and 37ºC, with maximum activity and yield at 30ºC. When protease production was tested in media with different initial pH, maximum activity was observed when cultivation was carried out at 30ºC and initial pH ranging from 6.0 to 8.0. Higher activity was observed when feathers or feather meal were used as growth substrates, followed by soybean meal. The addition of carbohydrates or surfactants to feather broth resulted in decrease in keratinolytic activity.

BIP Article

Proteolytic enzymes are largely used in the industry for biotechnological applications involving the hydrolysis of protein substrates (Rao et al. 1998). Bacterial keratinases are of particular interest because of their action on insoluble keratin substrates, and generally on a broad range of protein substrates (Lin et al. 1995). These enzymes have been studied for de-hairing processes in the leather industry and hydrolysis of feather keratin, which is a by-product generated in huge amounts by the poultry industry. Feather hydrolysates produced by bacterial keratinases have been used as additives for animal feed (Williams et al. 1991). In addition, keratin hydrolysates have potential use as organic fertilizers, production of edible films and rare amino acids.

The Chryseobacterium sp. strain kr6 was isolated from waste of a poultry industry and was capable to completely degrade chicken feathers (Riffel et al. 2003). This work describes the effect of temperature, initial pH and substrates on keratinase production by Chryseobacterium sp. kr6 during growth on native feathers.

Results and Discussion

The strain of Chryseobacterium sp. kr6 grew well and completely degraded chicken feathers in the medium. This intense feather-degrading activity was achieved in the range of 25-37ºC and with initial pH adjusted from 6.0 to 8.0. No important growth neither proteolytic activity were observed during cultivation of the strain at 42ºC or higher and pH 9.0 or higher. Maximum enzyme activity and enzyme yields were observed at 30ºC and pH ranging from 6.0 to 7.0. Maximum biomass was obtained with more alkaline pH values.

Production of keratinase activity was similar when the strain kr6 was grown in raw feathers or feather meal, but decreased with other proteinaceous substrates. The addition of glucose, and markedly sucrose or lactose, resulted in strong inhibition of keratinase production. Other additives such as the surfactants Tween 80 and Triton X-100 also caused reduction in protease yields.

Although the production of proteases in complex growth media often promotes exuberant growth and high enzyme yields, their expensive cost makes them unsuitable for a large-scale production. It seems more adequate to use raw materials like some wastes from the food industry as a basis of the culture media. The strain kr6 produced higher keratinase yields in feather meal and raw feathers, which have been used as good substrates for production of other keratinolytic enzymes.

Keratinases have enormous potential applications in processing waste in the poultry and leather industries. In this study, the optimum conditions for keratinase synthesis by the Chryseobacterium strain kr6 were determined, which is an essential step for the production of adequate amounts for application in research of feed and other areas.

References

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RAO, M.B.; TANKSALE, A.M.; GHATGE, M.S. and DESHPANDE, V.V. Molecular and biotechnological aspects of microbial proteases. Microbiology and Molecular Biology Reviews, September 1998, vol. 62, no. 3, p. 597-635.

RIFFEL, A.; LUCAS, F.S.; HEEB, P. and BRANDELLI, A. Characterization of a new keratinolytic bacterium that completely degrades native feather keratin. Archives of Microbiology, April 2003, vol. 179, no. 4, p. 258-265.

WILLIAMS, C.M.; LEE, C.G.; GARLICH, J.D. and SHIH, J.C.H. Evaluation of a bacterial feather fermentation product, feather-lysate, as a feed protein. Poultry Science, January 1991, vol. 70, no. 1, p. 85-94.