The microbial degradation of silk: a laboratory investigation

A few bacterial species, mostly gram-negatives, were found to attach themse lves and grow on silk buried in soil. On the contrary, no fungi were isolat ed in such experiments. Growth was more abundant on raw silk (composed of s ericin and fibroin) than on degummed silk (fibroin only) indicating that th e majority of these bacteria use sericin rather than fibroin for growth. El ectron microscopy demonstrated that bacteria formed a biofilm on the fabric and caused extensive damage to the fibers resulting in considerable reduct ion in the mechanical properties. Of the three main bacterial species isola ted from silk exposed to soil or by enrichment cultures of silk cocoons, on ly Pseudomonas (Burkholderia) cepacia appeared to be able to use fibroin as a sole source of carbon and nitrogen for growth. Indeed, in laboratory exp eriments, pure cultures of P. cepacia were found to form a well-developed b iofilm on fibroin, to hydrolyze fibroin, and to produce an extracellular en zyme attacking this protein. The reported data indicate that bacteria but n ot fungi may attack and degrade silk proteins and thus cause irreversible d amage to silk artifacts of artistic or historical interest. (C) 1999 Elsevi er Science Ltd. All rights reserved.