Bacterial degradation of natural rubber: a privilege of actinomycetes?

Using natural rubber latex as the sole source of carbon and energy 50 rubber-degrading bacteria were isolated. Out of those 50 isolates, 33 were identified as Streptomyces species and 8 as Micromonospora species. Screening of 1220 bacteria obtained from different culture collections revealed 46 additional rubber-degrading bacteria (Streptomyces 31 strains, Micromonospora 5, Actinoplanes 3, Nocardia 2, Dactylosporangium 1, Actinomadura 1, unidentified 3). All rubber-degrading isolates were identified as members of the actinomycetes, a large group of mycelium-forming Gram-positive bacteria. Interestingly no Gram-negative bacterium could be isolated. In most strains expression of extracellular rubber-degrading enzymes was repressed by glucose and/or succinate. The reduction of the average molecular mass of solution-cast films of natural rubber from 640000 to 25000 in liquid culture upon bacterial growth indicates the participation of an endo-cleavage mechanism of degradation.