Limonene (4-isopropenyl-1-methyl-cyclohexene), a monocyclic monoterpene, is the most widespread terpene in the world and is formed by more than 300 plants. (+)-(4R)-limonene is its most widespread form ([http://www.ncbi.nlm.nih.gov/pubmed/10224006|van der Werf et al., 1999]). Limonene is the major constituent of citrus essential oils and is used as a raw material for the chemical synthesis of terpene resin adhesives and flavor materials, such as menthol and carvone. So far, five different microbial biotransformation pathways for limonene have been proposed. In the middle branch, a soil Pseudomonassp. degradates limonene in the same way as Rhodococcus erythropolis DCL14, but its final product is 1-hydroxy-2-oxolimonene rather than 3-isopropenyl-6-oxoheptanoyl-CoA. The middle branch shows a pathway for (+)-(4R)-limonene; a similar pathway using many of the same enzymes is known for (-)-(4S)-limonene ([http://www.ncbi.nlm.nih.gov/pubmed/10224006|van der Werf et al., 1999]).