Formation of n-alkane-2-ones and n-alkane-2-ols from triglycerides by a black yeast, Aureobasidium

Abstract

The n-alkane-forming-strains were screened from soil by checking n-alkane-2-one (2-one) formation from both synthetic and natural triglycerides. All of the 2-one-accumulative strains were filamentous fungi with the exception of a black yeast (SM-25). The yeast (SM-25) was identified to be a strain which belongs to the genus Aureobasidium, and had the following interesting activity: extracellular accumulation of n-undecane-2-one (C 11-2-one) and n-undecane-2-ol (C 11-2-ol) in significant yields with consumption of lauric acid (C 12:0), a major component, in palm-kernel oil. The maximal accumulations of 2-ones and 2-ols were achieved in 4-d and 6-d cultures, respectively, with a subsequent decrease in their volume. The time-shift in the maximal accumulation suggests that 2-one is a precursor for 2-ol. When synthetic triglycerides were used as substrate, the yeast indicated a specific accumulation of n-pentane-2-one (C 5-2-one) in a high yield and of n-pentane-2-ol (C 5-2-ol) in a low yield with consumption of tricaproin (caproic triglyceride). In tricaprylin-, tricaprin- and trilaurin-basal media, accumulation of 2-one and 2-ol was small or undetectable. Although there is a clear discrepancy between molecular species of 2-ones and 2-ols formed from palm-kernel oil and synthetic triglycerides, we don't have a clear explanation for this yet. In order to clarify the metabolic pathway in the yeast for n-alkane-2-one or n-alkane-2-ol formation from fatty acids, the metabolites from 2-ones and 2-ols were characterized. Subsequently, the occurrence of interconversion between n-alkane-2-one and n-alkane-2-ol by the yeast cells was demonstrated. This observation did not lead us to a definite answer to the question: which is the upstream intermediate in the fatty-acid-metabolic pathway, 2-one or 2-ol?