Knockout of the two ldh genes has a major impact on peptidoglycan precursor synthesis in Lactobacillus plantarum

Most bacteria synthesize muramyl-pentapeptide peptidoglycan precursors ending with a D-alanyl residue (e.g., UDP-N-acetylmuramyl-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Ala), However, it was recently demonstrated that other types of precursors, notably D-lactate-ending molecules, could be synthesized by several Lactic acid bacteria. This particular feature leads to vancomycin resistance, Vancomycin is a glycopeptide antibiotic that blocks cell wall synthesis by the formation of a complex with the extremity of peptidoglycan precursors, Substitution of the terminal D-alanine by D-lactate reduces the affinity of the antibiotic for its target, Lactobacillus plantarum is a lactic acid bacterium naturally resistant to vancomycin, It converts most of the glycolytic pyruvate to L- and D-lactate by using stereospecific enzymes designated L- and D-lactate dehydrogenases, respectively, In the present study, we show that L. plantarum actually synthesizes D-lactate-ending peptidoglycan precursors, We also report the construction of a strain which is deficient for both D- and L-Lactate dehydrogenase activities and which produces only trace amounts of D- and L-lactate. As a consequence, the peptidoglycan synthesis pathway is drastically affected, The wild-type precursor is still present, but a new type of D-alanine-ending precursor is also synthesized in large quantities, which results in a highly enhanced sensitivity to vancomycin.