DECOMPOSITION OF NATIVE KERATIN BY STREPTOMYCES FRADIAE

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Abstract
Previous studies of microbial digestion of keratin used denatured keratin or presented inadequate evidence that keratin was digested. In this study, wool and feathers were sterilized with gaseous ethylene oxide without producing detectable alterations in the chemical composition or enzymatic resistance of the keratin, and so were considered to be undenatured. Strains of S. fradiae were unique in their ability to digest native keratin; 80 to 90% of the dry weight of wool and feathers were solubilized in 3 days in optimum conditions (agitation at 37[degree]C, in medium with initial pH of 7.7, containing keratin as sole source of C and N). Ca and Mg ions stimulated the attack on wool. Wool sterilized with chloroform was digested equally well. Soluble sulfhydryl compounds equivalent to 66% of cystine present in the wool substrate accumulated in cultures of S. fradiae. during wool digestion. Paper chromatography revealed 3 sulfhydryl compounds, none of which was cysteine or glutathione. NH3 formed during wool digestion accounted for 75% of N in the wool. Cell-free broths from cultures of S. fradiae digested keratins and casein rapidly, with optimum activity at pH 8.5 to 10. Brief heating destroyed this activity whereas dialysis did not. In conclusion, growing cultures of S. fradiae rapidly and completely digested native keratin, apparently by a mechanism similar to that proposed for the digestion of wool by insects: that is, by the combined attack of reducing and proteolytic agents, neither of which alone could account for the extent of keratin digestion that the organism accomplished.