Disruption of the alsSD operon of Enterococcus faecalis impairs growth on pyruvate at low pH

REPIZO, GUILLERMO; MORTERA, PABLO; MAGNI, CHRISTIAN

MICROBIOLOGY-UK

SOC GENERAL MICROBIOLOGY

Lugar: Basingstoke Road, Spencers Wood, Reading, RG7 1AG, UK; Año: 2011 vol. 157 p. 2708 - 2719

1350-0872

Diacetyl and acetoin are pyruvate-derived metabolites excreted by many micro-organisms, and areimportant in their physiology. Although generation of these four-carbon (C4) compounds inEnterococcus faecalis is a well-documented phenotype, little is known about the gene regulationof their biosynthetic pathway and the physiological role of the pathway in this bacterium. In thiswork, we identified the genes involved in C4 compound biosynthesis in Ent. faecalis and reporttheir transcriptional analysis. These genes are part of the alsSD bicistronic operon, whichencodes a-acetolactate synthase (AlsS) and a-acetolactate decarboxylase (AlsD). Our studiesshowed that alsSD operon transcription levels are maximal during the exponential phase ofgrowth, decreasing thereafter. Furthermore, we found that this transcription is enhanced uponaddition of pyruvate to the growth medium. In order to study the functional role of the alsSDoperon, an isogenic alsSD mutant strain was constructed. This strain lost its capacity to generateC4 compounds, confirming the role of alsSD genes in this metabolic pathway. In contrast to thewild-type strain, the alsSD-deficient strain was unable to grow in LB medium supplemented withpyruvate at an initial pH of 4.5. This dramatic reduction in growth parameters for the mutant strainwas simultaneously accompanied by the inability to alkalinize the internal and external mediumunder these conditions. In sum, these results suggest that the decarboxylation reactions related tothe C4 biosynthetic pathway give enterococcal cells a competitive advantage during pyruvatemetabolism at low pH