Degradation of phenylalkanes and characterization of aromatic intermediates acting as growth inhibiting substances in hydrocarbon utilizing yeast Candida maltosa

Phenylalkanes constitute up to 28% of refined gasoline fuel oil. Because of the widespread use of petroleum, oil and gasoline and the environmental risks associated with accidental spills, the ability to degrade these compounds is a major goal of environmental research. We here report our investigation in the use of yeast to degrade phenylalkanes. Among the studied strains of the genera Candida, Hansenula, Pichia, Saccharomyces and Arxula the alkane-assimilating ones grew on phenylalkanes with alkyl side chains longer than C7, utilizing them as sole carbon and energy source. Detailed studies on phenylalkane metabolism were carried out with Candida maltosa SBUG 700. During incubation of this yeast with phenyldecane, phenyloctane and phenylhexane 4-phenylbutanoic acid, 4-phenyl-3-butenoic acid and phenylacetic acid were produced whereas benzoic acid was the only detectable degradation product of phenylnonane and phenylheptane. Phenylacetic acid and benzoic acid were accumulated in high amounts due to the inability of C. maltosa to oxidize these acids further. Oxidation of phenylalkanes was inhibited in the presence of 1-aminobenzotriazole acting as inhibitor of cytochrome P450. Furthermore, toxic effects of benzoic acid and phenylacetic acid amplified by fallen pH values of growth medium strongly inhibited the metabolism of phenylalkanes as well as glucose assimilation and this led to incomplete phenylalkane degradation.