Physiological and chemical investigations into microbial degradation of synthetic poly(cis-1,4-isoprene)

Streptomyces coelicolor 1A and Pseudomonas citronellolis were able to degra de synthetic high-molecular-weight poly(cis-1,4-isoprene) and vulcanized na tural rubber. Growth on the polymers was poor but significantly greater tha n that of the nondegrading strain Streptomyces lividans 1326 (control). Mea surement of the molecular weight distribution of the polymer before and aft er degradation showed a time dependent increase in low-molecular-weight pol ymer molecules for S. coelicolor 1A and P. citronellolis, whereas the molec ular weight distribution for the control (S. lividans 1326) remained almost constant. Three degradation products were isolated from the culture fluid of S. coelicolor 1A grown on vulcanized rubber and were identified as (6Z)- 2,6-dimethyl -10-oxo-undec-6-enoic acid, (5Z)-6-methyl-undec-5-ene-2,9-dion e, and (5Z,9Z)-6,10 dimethyl-pentadec 5,9-diene-2,13-dione. An oxidative pa thway from poly(cis-1,4-isoprene) to methyl-branched diketones is proposed. It includes (i) oxidation of an aldehyde intermediate to a carboxylic acid , (ii) one cycle of beta-oxidation, (iii) oxidation of the conjugated doubl e bond resulting in a beta-keto acid, and (iv) decarboxylation.