Towards the bio-production of trans-carveol and carvone from limonene: induction after cell growth on limonene and toluene

Abstract

Rhodococcus opacus PW4 cells were found to produce trans- and cis-carveol and/or carvone as result of limonene metabolism, depending on the type and concentration of the carbon source used for cell growth. In aqueous systems, cells grown on ethanol and toluene only produced trans-carveol, whilst cells grown on limonene and on toluene with a larger head-space available produced both trans-carveol and carvone. In biphasic systems, limonene was converted to trans- and cis-carveol as well as to carvone, regardless of the carbon source used, although carveol and carvone production rates were higher in toluene and limonene grown cells, respectively. A good and stable emulsion was obtained in a magnetically stirred two-phase reactor but both trans-carveol and carvone were produced at low rates: 0.08 and 0.02 nmol/min mg prot, respectively. No cis-carveol was formed. When (−)-carveol was added, carvone production increased 4.7 fold to 0.12 nmol/min mg prot. Using an aerated two-phase reactor, carvone production was enhanced even with cells grown on toluene. The highest trans- and cis-carveol and carvone production rates were attained with cells grown on limonene by continuously supplying limonene to the reactor through the air stream, carvone production reaching 0.58 nmol/min mg prot. The best trans-/ cis-carveol ratio (2.26) was observed with cells grown on toluene when limonene was supplied in the gas phase. When 50 mM limonene was added initially, carvone was produced 27.9 and 141.4 times faster than trans-carveol with cells grown on toluene and limonene, respectively.