Structural organization of StyA/StyB- and StyA1/StyA2B-gene clusters from Rhodococcus opacus 1CP. The styABCD cluster of strain 1CP harboring a styrene monooxygenase (StyA) and the associated oxidoreductase (StyB), as well as the styrene oxide isomerase (StyC) and the phenylacetaldehyde dehydrogenase (StyD) (Oelschlägel et al. 2014). Upstream two putative transcriptional regulators (AraC family) are shown. Rhodococcus sp. ST-5 harbors a similar cluster (Toda and Itoh 2012). The StyA1/StyA2B system of strain 1CP containing the styrene monooxygenase StyA1 and the self-sufficient StyA2B where the StyA part is fused to the StyB subunit. ORF2x directly upstream from the genes responsible for conversion of styrene encodes a PaaX-like regulator. This regulator is responsible for activation of the styrene upper pathway metabolism product phenylacetic acid, which is then converted in their CoA-associated product in order to be available for the Krebs cycle. SDR short-chain dehydrogenase, DLH dienelactone hydrolase (Patrauchan et al. 2005; Tischler et al. 2012). Pseudomonas sp. Y2 exhibits a styABCD cluster and the PaaX-like regulator. In comparison to rhodococci Pseudomonas species feature two histidine sensor kinases StyS and StyR.