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, 66 (9), 3680-5

Physiological and Chemical Investigations Into Microbial Degradation of Synthetic Poly(cis-1,4-isoprene)

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Physiological and Chemical Investigations Into Microbial Degradation of Synthetic Poly(cis-1,4-isoprene)

H B Bode et al. Appl Environ Microbiol.

Abstract

Streptomyces coelicolor 1A and Pseudomonas citronellolis were able to degrade synthetic high-molecular-weight poly(cis-1,4-isoprene) and vulcanized natural rubber. Growth on the polymers was poor but significantly greater than that of the nondegrading strain Streptomyces lividans 1326 (control). Measurement of the molecular weight distribution of the polymer before and after degradation showed a time-dependent increase in low-molecular-weight polymer molecules for S. coelicolor 1A and P. citronellolis, whereas the molecular 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-dione, and (5Z,9Z)-6, 10-dimethyl-pentadec-5,9-diene-2,13-dione. An oxidative pathway 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 double bond resulting in a beta-keto acid, and (iv) decarboxylation.

Figures

FIG. 1
FIG. 1
Structures of poly(cis1,4-isoprene) degradation products. Compound 2, (6Z)-2,6-dimethyl-10-oxo-undec-6-enoic acid (C13H22O3; molecular weight, 226.32); compound 3, (5Z)-6-methyl-undec-5-ene-2,9-dione (C12H20O2; molecular weight, 196.29); compound 4, (5Z,9Z)-6,10-dimethyl-pentadec-5,9-diene-2,13-dione (C17H28O2; molecular weight, 264.41).
FIG. 2
FIG. 2
Growth of selected bacteria on synthetic poly(cis-1,4-isoprene). Twenty Erlenmeyer flasks (100 ml), each containing 20 ml of growth medium with or without rubber, were inoculated with the strain of interest and incubated at 30°C for 10 weeks. Two flasks were harvested at 2-week intervals, and the protein concentrations were determined. Evaporated water was replaced by the addition of sterile water. Mean values of the two determinations are given. A noninoculated sterile culture with rubber served as a control. P.c., P. citronellolis.
FIG. 3
FIG. 3
Calibration of the GPC system with narrowly distributed poly(cis-1,4-isoprene) standards. The relationship between the elution volumes (in milliliters) at the peak maximum (solid circles) and the molecular masses of the standards and the relationship between the refractive index detector signals [rel. W(logM)] and the molecular masses of the standards are shown. The eluent was toluene and the flow rate was 1 ml/min.
FIG. 4
FIG. 4
GPC elution profiles for the residual polymers after incubation of S. lividans 1326, S. coelicolor 1A, and P. citronellolis with synthetic poly(cis-1,4-isoprene) for 6 weeks (black line) and 2 weeks (medium grey line) and at zero time (light grey line). rel. W(logM), refractive index detector signal.
FIG. 5
FIG. 5
Hypothetical biochemical route for degradation of poly(cis-1,4-isoprene) to compounds 2 to 4 by S. coelicolor 1A.

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