The ZbYME2 gene from the food spoilage yeast Zygosaccharomyces bailii confers not only YME2 functions in Saccharomyces cerevisiae, but also the capacity for catabolism of sorbate and benzoate, two major weak organic acid preservatives

A factor influencing resistances of food spoilage microbes to sorbate and b enzoate is whether these organisms are able to catalyse the degradation of these preservative compounds. Several fungi metabolize benzoic acid by the beta -ketoadipate pathway, involving the hydroxylation of benzoate to 4-hyd roxybenzoate. Saccharomyces cerevisiae is unable to use benzoate as a sole carbon source, apparently through the lack of benzoate-4-hydroxylase activi ty. However a single gene from the food spoilage yeast Zygosaccharomyces ba ilii, heterologously expressed in S. cerevisiae cells, can enable growth of the latter on benzoate, sorbate and phenylalanine. Although this ZbYME2 ge ne is essential for benzoate utilization by Z. bailii, its ZbYme2p product has little homology to other fungal benzoate-4-hydroxylases studied to date , all of which appear to be microsomal cytochrome P450s. Instead, ZbYme2p h as strong similarity to the matrix domain of the S. cerevisiae mitochondria l protein Yme2p/Rna12p/Prp12p and, when expressed as a functional fusion to green fluorescent protein in S. cerevisiae growing on benzoate, is largely localized to mitochondria. The phenotypes associated with loss of the nati ve Yme2p from S. cerevisiae, mostly apparent in yme1,yme2 cells, may relate to increased detrimental effects of endogenous oxidative stress. Heterolog ous expression of ZbYME2 complements these phenotypes, yet it also confers a potential for weak acid preservative catabolism that the native S. cerevi siae Yme2p is unable to provide. Benzoate utilization by S. cerevisiae expr essing ZbYME2 requires a functional mitochondrial respiratory chain, but no t the native Yme1p and Yme2p of the mitochondrion.