Characterisation of p-hydroxycinnamate catabolism in a soil Actinobacterum

p-Hydroxycinnamates, such as p-coumarate and ferulate, are components of plant cell walls and have a number of commercial applications. Previously, we had shown that the soil Actinobacterium Rhodococcus jostii RHA1 (RHA1) grows on ferulate, catabolizing it via vanillate and the ß-ketoadipate pathway. We used transcriptomics to identify genes in RHA1 that were specifically up-regulated during growth on ferulate. These include three operons predicted to encode the uptake and ß-oxidative deacetylation of ferulate and p-coumarate: couHLT, couMNO and couR. A couL mutant did not grow on p-coumarate, ferulate or their dihydro derivatives, but grew on vanillate. Purified CouL catalyzed the thioesterification of several p-hydroxycinnamates. Among the tested substrates, the best were p-coumarate and caffeate (kcat/KM ~400 mM-1s-1), and sinapate was not transformed. Of these, p-coumarate was also RHA1's preferred growth substrate. Although the data indicate that p-hydroxycinnamates are catabolized via ß-oxidation, the pathway lacks a typical ß-ketothiolase. The data further suggest the involvement of two formaldehyde detoxification pathways in vanillate catabolism. This study augments our understanding of the bacterial catabolism of biomass and facilitates the production of aromatics from renewable feedstocks. Overall design: Transcriptomes of R. jostii RHA1 from ferulate and benzoate cultures were analysed using Ion PGMTM system.