The microbial degradation of silk: a laboratory investigation

A few bacterial species, mostly gram-negatives, were found to attach themselves and grow on silk buried in soil. On the contrary, no fungi were isolated in such experiments. Growth was more abundant on raw silk (composed of sericin and fibroin) than on degummed silk (fibroin only) indicating that the majority of these bacteria use sericin rather than fibroin for growth. Electron microscopy demonstrated that bacteria formed a biofilm on the fabric and caused extensive damage to the fibers resulting in considerable reduction in the mechanical properties. Of the three main bacterial species isolated from silk exposed to soil or by enrichment cultures of silk cocoons, only Pseudomonas (Burkholderia) cepacia appeared to be able to use fibroin as a sole source of carbon and nitrogen for growth. Indeed, in laboratory experiments, pure cultures of P. cepacia were found to form a well-developed biofilm on fibroin, to hydrolyze fibroin, and to produce an extracellular enzyme attacking this protein. The reported data indicate that bacteria but not fungi may attack and degrade silk proteins and thus cause irreversible damage to silk artifacts of artistic or historical interest.