Colonization and disintegration of tire rubber by a colonial mutant of Nocardia.

Forty-seven percent of a tire tread strip with a natural rubber content of 100 phr (parts per hundred of rubber) was completely mineralized by a mutant strain, Rc, of the rubber-degrading organism, Nocardia sp. strain 835A, while 34% was disintegrated into very small particles after a cultivation period of 8 weeks.

Degradation of the rubber in truck tires by a strain of Nocardia.

A strip of tread compound cut from a truck tire was degraded only slightly when it was used as the sole growth substrate for a strain of Nocardia. On the contrary, its degradation was markedly enhanced by addition of a strip cut from a latex glove which the organism readily utilized as a growth substrate. When a glove strip was added, the biomass concentration in the experimental flask became more than 10-fold higher than the control without a glove strip and the colonization of the tire strip was significantly enhanced. After 8 weeks' cultivation, about 28% of the tire strip was disintegrated into very small black particles (mostly less than 30 microns in diameter) and the weight of the remaining unchanged portion of the strip was about 49% of the initial weight. Four kinds of truck tire treads were attacked in differing degrees by the organism under the same conditions. The treads containing more than 70 phr (parts per hundred of rubber) of natural rubber were considerably attacked, while those with a natural rubber content of less than 55 phr were attacked only slightly. The microbial activity against the rubber in the side wall of a truck tire was relatively high, but the inner liner was hardly attacked and the bead rubber not at all.

Rubber-degrading enzyme from a bacterial culture.

Rubber-degrading activity was found in the extracellular culture medium of Xanthomonas sp. strain 35Y which was grown on natural rubber latex. Natural rubber in the latex state was degraded by the crude enzyme, and two fractions were separately observed by gel permeation chromatography of the reaction products. One fraction was of higher molecular weight (HMW) with a very wide MW distribution from 10 to 10, and the other fraction was of lower molecular weight (LMW) with a MW of a few hundred. H-nuclear magnetic resonance spectra of the partially purified fractions were those expected of cis-1,4-polyisoprene mixtures with the structure OHC-CH(2)-(-CH(2)-C(-CH(3)) = CH-CH(2)-)(n)-CH(2)-C(=O)-CH(3), with average values of n of about 113 and 2 for HMW and LMW fractions, respectively. The LMW fraction consisted mostly of one component in gas-liquid chromatography as well as in gel permeation chromatography, and the main component was identified as 12-oxo-4,8-dimethyl trideca-4,8-diene-1-al (acetonyl diprenyl acetoaldehyde, A(l)P(2)A(t)) by C-nuclear magnetic resonance and gas chromatography-mass spectra. Not only the latices of natural and synthetic isoprene rubber, but also some kinds of low-MW polyisoprene compounds of cis-1,4 type, were degraded by the crude enzyme. The rubber-degrading reaction was found to be at least partly oxygenase catalyzed from the incorporation of O into A(l)P(2)A(t) under an O(2) atmosphere.

Microbial degradation of natural rubber vulcanizates.

An actinomycete, Nocardia sp. strain 835A, grows well on unvulcanized natural rubber and synthetic isoprene rubber, but not on other types of synthetic rubber. Not only unvulcanized but also various kinds of vulcanized natural rubber products were more or less utilized by the organism as the sole source of carbon and energy. The thin film from a latex glove was rapidly degraded, and the weight loss reached 75% after a 2-week cultivation period. Oligomers with molecular weights from 10 to 10 were accumulated during microbial growth on the latex glove. The partially purified oligomers were examined by infrared and H nuclear magnetic resonance and C nuclear magnetic resonance spectroscopy, and the spectra were those expected of cis-1, 4-polyisoprene with the structure, OHC-CH(2)-[-CH(2)-C(-CH(3))=CH -CH(2)-](n)-CH(2)-C(=O)- CH(3), with average values of n of about 114 and 19 for the two oligomers.

Effect of methyl substitution on microbial degradation of linear styrene dimers by two soil bacteria.

The microbial degradation of 10 linear unsaturated dimers (I to IV) prepared from styrene and o-, m-, or p-methylstyrene was investigated with two soil bacteria, Alcaligenes sp. strain 559 and Pseudomonas sp. strain 419. The two strains decomposed styrene dimer I and all styrene-methylstyrene codimers II and III, but methylstyrene homodimers IV remained intact. The degradation rates of codimers II and III of o- and m-methylstyrenes were found to depend on both their structure and the strain used; i.e., Alcaligenes sp. strain 559 decomposed III faster than II, whereas the reverse order (II > III) was obtained with Pseudomonas sp. strain 419. In biodegradation by the former strain, the codimers were degraded faster in the presence of styrene dimer I than in its absence, but no such effect of dimer I was observed with the latter.