Development of a Chemically Defined Medium to Assay the Metabolism of Lactic Acid Bacteria

Abstract

The purpose of this study was to develop a chemically-defined medium that is capable of supporting and detecting the metabolism of nutritionally-fastidious Lactic Acid Bacteria (LAB). The resultant Kim Menon Sturino (KMS) medium is comprised of only twelve chemically-defined ingredients. In order to increase the bioavailability of hydrophobic chemical additives, such as the isoflavone genistein (4',5,7-trihydroxyisoflavone), tween 80 was incorporated into the final medium at high levels (10% v/v). Furthermore, a commercial redox indicator was supplemented to the final formulation in order to facilitate the indirect assessment of cellular metabolism through the direct measurement of medium coloration. As proof of concept, the KMS medium was used to identify LAB with specific enzyme activities of interest, specifically β-glycoside hydrolase activity. In this model system, LAB were screened for their capacity to catabolize genistin (Gin^(+)), a glucoside (glycone) of genistein (genistein 7-O-β-D-glucoside) or its complementary aglycone, genistein (Gen^(+)). Of the fifteen strains screened, none were Gen^(+) while L. pentosus was reproducibly Gin^(+). As a result of this work, we conclude that L. pentosus expresses one or more β-glycoside hydrolases capable of hydrolyzing the glucose associated with genistin and fermenting it.