Design of catabolic cassettes for styrene biodegradation.
A broad-host range metabolic cassette has been designed that, under the control of the Ptac promoter, expresses the sytABCD catabolic genes from Pseudomonas sp. Y2, which are responsible for the transformation of styrene into phenylacetic acid (styrene upper pathway). This novel cassette confers to phenylacetic acid-degrading bacteria the ability to grow efficiently on styrene as the sole carbon and energy source. By combining both the sty cassette and the archetypal pWW0 TOL plasmid into the well-known Pseudomonas putida F1 aromatic biodegrader, we have constructed a novel derivative strain that shows one of the largest degradative potentials so far described for aromatic hydrocarbons, because it is able to use BTEX compounds (benzene, toluene, ethylbenzene and xylenes) and styrene as a source of carbon and energy. Furthermore, the sty cassette was engineered within a mini-transposon and endowed with a gene containment system, based on the toxic effect of the colicin E3 RNase, to reduce its lateral spread to other hosts. This contained cassette lacks defined transcriptional regulatory signals and, thus, it becomes an alternative strategy to select recombinant strains that efficiently express the desired phenotype from housekeeping regulatory elements.