Recent advances in understanding resin acid biodegradation: microbial diversity and metabolism

Resin acids are tricyclic diterpenoids that are found in the oleoresin of c oniferous trees. Resin-acid-degrading microorganisms are ubiquitous in the environment. The bacterial isolates that grow on resin acids as sole organi c substrates are physiologically and phylogenetically diverse, and include psychrotolerant, mesophilic, and thermophilic bacteria. Recent studies of t he biodegradation of resin acids by these organisms have demonstrated that in gram-negative bacteria, distinct biochemical pathways exist for the degr adation of abietane- and pimerane-type resin acids. One of these organisms, Pseudomonas abietaniphila BKME-9, harbors a convergent pathway that channe ls the nonaromatic abietanes and dehydroabietic acid into 7-oxodehydroabiet ic acid. This dioxygenolytic pathway is encoded by the recently cloned and sequenced dit gene cluster. The dit cluster encodes the ferredoxin and the alpha- and beta-subunits of a new class of ring-hydroxylating dioxygenases as well as an extradiol ring-cleavage dioxygenase. Although it was previous ly thought that resin acids are very recalcitrant under anoxic conditions, recent investigations have demonstrated that they are partially metabolized under anoxic conditions by undefined microorganisms. The anaerobic degrada tion of resin acids principally generates aromatized and decarboxylated pro ducts (such as retene) that are thought to persist in the environment.