Genetic Determinants of Hydroxycinnamic Acid Metabolism in Heterofermentative Lactobacilli

The metabolism of secondary plant metabolites, including phenolic compounds, by food-fermenting lactobacilli is a significant contributor to the safety, quality, and nutritional quality of fermented foods. The enzymes mediating hydrolysis, reduction, and decarboxylation of phenolic acid esters and phenolic acids in lactobacilli, however, are not fully characterized. The genomic analyses presented here provide evidence for three novel putative phenolic acid reductases. Matching comparative genomic analyses with phenotypic analysis and quantification of gene expression indicates that two of the three putative phenolic acid reductases, Par1 and HcrF, are involved in reduction of hydroxycinnamic acids to phenylpropionic acids; however, the activity of Par2 may be unrelated to phenolic acids and recognizes other secondary plant metabolites. These findings expand our knowledge on the metabolic potential of lactobacilli and facilitate future studies on activity and substrate specificity of enzymes involved in metabolism of phenolic compounds.