ELECTROPHORETIC PATTERN OF PEPTIDOGLYCAN HYDROLASES, A NEW TOOL FOR BACTERIAL SPECIES IDENTIFICATION - APPLICATION TO 10 LACTOBACILLUS SPECIES

Lactobacilli have been used as industrial starters for a long time, bu t in many cases their phenotypic identification is still neither easy nor reliable. previously we observed that the cell wall peptidoglycan hydrolases of Lactobacillus helveticus were highly conserved enzymes; the aim of the present work was to determine whether peptidoglycan hyd rolase patterns obtained by renaturing SDS-PAGE could be of interest i n the identification of lactobacilli species. For that purpose, the pe ptidoglycan hydrolase patterns of 94 strains of lactobacilli belonging to 10 different species were determined; most of the species studied are used either in dairy, meat, bakery or vegetable fermentations: L. helveticus, L. acidophilus, L. delbrueckii, L. brevis, L. fermentum, L . jensenii, L. plantarum, L. sake, L. curvatus and L. reuteri. Within a species, the strains exhibited highly similar patterns: the apparent molecular weights of the lytic bands were identical, with only slight variations of intensity. Moreover, each species, including phylogenet ically close species such as L. sake and L. curvatus, or L. acidophilu s and L. helveticus, gave a different pattern. Interestingly, the clos er the species were phylogenetically, the more related were their patt erns. The sensitivity of the method was checked using various quantiti es of L. acidophilus cells: a peptidoglycan hydrolase extract of 5 x 1 0(6) cells was sufficient to obtain an informative pattern, as was a s ingle colony. Finally, the method was also successfully applied to dis tinguish two Carnobacterium species. In conclusion, the electrophoreti c pattern of peptidoglycan hydrolases is proposed as a new tool for la ctobacilli identification: it is rapid, sensitive and effective even f or phylogenetically close species. Furthermore, this work provides the first evidence of the potential overall taxonomic value of bacterial peptidoglycan hydrolases.