Abstract
Knowledge is scarce about the degradation of ketones in yeasts. For bacteria a subterminal degradation of alkanes to ketones and their further metabolization has been described which always involved Baeyer-Villiger monooxygenases (BVMOs). In addition, the question has to be clarified whether alkenes are converted to ketones, in particular for the oil degrading yeast Candida maltosa little is known. In this study we show the degradation of the aliphatic ketone dodecane-2-one by Candida maltosa and the related yeasts Candida tropicalis, Candida catenulata and Candida albicans as well as Trichosporon asahii and Yarrowia lipolytica. One pathway is initiated by the formation of decyl acetate, resulting from a Baeyer-Villiger-oxidation of this ketone. Beyond this, an initial reduction to dodecane-2-ol by a keto reductase was clearly shown. In addition, two different ways to metabolize dodec-1-ene were proposed. One involved the formation of dodecane-2-one and the other one a conversion leading to carboxylic and dicarboxylic acids. Furthermore the induction of ketone degrading enzymes by dodecane-2-one and dodec-1-ene was shown. Interestingly, with dodecane no subterminal degradation products were detected and it did not induce any enzymes to convert dodecane-2-one.
Highlights
Aliphatic hydrocarbons are major components of natural gasoline and crude oil
Yeast strains and culture conditions Experiments were carried out using Candida maltosa SBUG 700, Candida tropicalis SBUG 1019, Candida catenulata SBUG 512, Yarrowia lipolytica SBUG 1888, Trichosporon asahii SBUG 833 and Candida albicans SBUG 5121 which are deposited at the strain collection of the Department of Biology of the University of Greifswald (SBUG) from where they can be obtained upon request
Biotransformation of dodecane-2-one, dodec-1-ene and dodecane by growing yeast cells All the investigated yeasts C. maltosa, C. albicans, C. catenulata, C. tropicalis, Y. lipolytica and T. asahii and were able to grow with dodecane-2-one (1) as a sole source of carbon and energy
Summary
Aliphatic hydrocarbons (alkanes) are major components of natural gasoline and crude oil. Alkanes can be found in wax layers of plants and animals to reduce their loss of water by evaporation (Cheesbrough and Kolattukudy 1988) These mostly very hydrophobic substances can be used as sole carbon and energy sources for microbial growth. In most cases especially in eukaryotic microorganisms - the degradation of alkanes is initiated by cytochrome P450 monooxygenases The function of these enzymes is the oxidation of the n-alkanes to alcohols and the ω-hydroxylation of fatty acids (Scheller et al 1998). The availability of only short-chain hydrocarbons as carbon source results in a complete degradation to acetyl-CoA. This is amongst others used for the de novo fatty acid synthesis under requirement of biotin as cofactor for carboxylases (Tehlivets et al 2007). In case that long-chain hydrocarbons are available as well, these can be converted to fatty acids directly and in conclusion no carboxylation and no biotin is required (Schauer 1988)
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