Bacterial Degradation of Natural and Synthetic Rubber

The degradation of natural rubber (NR), synthetic poly(cis-1,4-isoprene) (SR), and cross-linked NR (latex gloves) by Gram-positive and Gram-negative bacteria was analyzed by weight loss, gel permeation chromatography, and determination of the protein content. Weight losses of 11−18% and an increase in protein up to 850 μg/mL after incubation of Nocardia sp. DSMZ43191, Streptomyces coelicolor, Streptomyces griseus, bacterial isolate 18a, Acinetobacter calcoaceticus, and Xanthomonas sp. with latex gloves as a carbon source indicated degradation of the polymer. An increase of protein up to 1250 μg/mL was obtained upon incubation of the bacteria with SR. No or only little weight losses and no increase in the protein content were found for nondegrading control strains such as Streptomyces lividans and Streptomyces exfoliatus and for mutants of degrading strains of S. coelicolor and S. griseus, which have been identified by their inability to produce clearing zones on opaque latex agar. Measurement of the average molecular weight of synthetic rubber before and after degradation showed a time-dependent shift to lower values for the degrading strains. Diketone derivates of oligo(cis-1,4-isoprene) were identified as metabolites of rubber degradation. An oxidative degradation pathway of poly(cis-1,4-isoprene) to acetyl-coenzymeA and propionyl-coenzymeA by β-oxidation is suggested for bacterial degradation of isoprene rubber.