Molecular and functional characterization of Lactobacillus sanfranciscensis strains isolated from sourdoughs

Fifty isolates of Lactobacillus sanfranciscensis from Italian sourdoughs were identified and typed by a polyphasic approach which included genotypic and phenotypic criteria. Genotypic diversity was characterized by Ribosomal Intergenic Spacer Analysis (RISA) of PCR amplified 16S–23S rDNA spacer region, denaturing gradient gel electrophoresis (DGGE) of PCR amplified rpoB (β subunit of RNA polymerase) gene, and rep-PCR (PCR amplification of repetitive bacterial DNA elements) analyses. The RISA analysis produced a unique electrophoretical profile of four bands (ranging from 300 to 600 bp) for all L. sanfranciscensis isolates. The DGGE analysis of rpoB gene allowed the subdivision of isolates in four clusters. The resolution found by using rep-PCR with primers BOXA1R and REP1R-I/REP2-I allowed the widening of the level of isolates heterogeneity. Phenotypic diversity was evaluated by Biolog System and characterization of several technological traits (e.g., acidification kinetics, proteinase and peptidase activities). L. sanfranciscensis isolates used a large varieties of carbon sources such as dextrin, D-fructose, L-fucose, α-D-glucose, maltose, palatinose, L-rhanmose, L- and D,L-lactic acids and L-methionine. The acidification activity and related quotient of fermentation, and the peptidase (PepN, PepV, PepT, PepI, PepX, PepQ and PepR) activities markedly varied among strains. The same was found concerning the capacity to liberate amino acids during sourdough fermentation. This study could be considered as an example of a computerized analysis of the genotypic and phenotypic traits to reliably and rapidly differentiate sourdough isolates. Although some L. sanfranciscensis isolates combined several technological traits, the association of more selected strains seemed to be a requisite to get optimal sourdough characteristics.