Transcriptomic Analysis ofRhodococcus opacusR7 Grown ono-Xylene by RNA-Seq

Xylenes are considered one of the most common hazardous sources of environmental contamination. The biodegradation of these compounds has been often reported, rarer the ability to oxidize theortho-isomer. Among fewo-xylene-degrading bacteria,Rhodococcus opacusR7 is well known for its capability to degrade diverse aromatic hydrocarbons and toxic compounds, includingo-xylene as only carbon and energy source. This work shows for the first time the RNA-seq approach to elucidate the genetic determinants involved in theo-xylene degradation pathway inR. opacusR7. Transcriptomic data showed 542 differentially expressed genes that are associated with the oxidation of aromatic hydrocarbons and stress response, osmotic regulation and central metabolism. Gene ontology (GO) enrichment and KEGG pathway analysis confirmed significant changes in aromatic compound catabolic processes, fatty acid metabolism,beta-oxidation, TCA cycle enzymes, and biosynthesis of metabolites when cells are cultured in the presence ofo-xylene. Interestingly, the most up-regulated genes belong to theakbgene cluster encoding for the ethylbenzene (Akb) dioxygenase system. Moreover, the transcriptomic approach allowed identifying candidate enzymes involved in R7o-xylene degradation for their likely participation in the formation of the metabolites that have been previously identified. Overall, this approach supports the identification of several oxidative systems likely involved ino-xylene metabolism confirming thatR. opacusR7 possesses a redundancy of sequences that converge ino-xylene degradation through R7 peculiar degradation pathway. This work advances our understanding ofo-xylene metabolism in bacteria belonging toRhodococcusgenus and provides a framework of useful enzymes (molecular tools) that can be fruitfully targeted for optimizedo-xylene consumption.