Comparative study on cell envelope‐associated proteinases in natural isolates of mesophilic lactobacilli

Abstract

Lactobacilli isolated from different natural sources were screened for the presence of cell envelope‐associated proteinases (Prt + strains). Among them 17 of 75 tested isolates were Prt + . All Prt + strains were producers of a serine‐type proteinase, since their proteolytic activity was inhibited by phenylmethylsulfonyl fluoride. Most of the natural isolates of mesophilic lactobacilli degraded only β‐casein such as Lactobacillus paracasei subsp. paracasei strains BGLI17 and BGLI18 and Lact. rhamnosus BGEN1. Only Lact. divergens BG742 cleaved all three, α‐, β‐ and κ‐caseins, even in the presence of Ca 2+ ions. Total DNA isolated from Lact. paracasei subsp. paracasei strains BGLI17 and BGLI18 hybridized to the lactococcal proteinase gene probes originated from Lactococcus lactis subsp. cremoris Wg2. Hybridization could not be linked to the plasmid DNA, and pulse‐field gel electrophoresis analysis suggested that the proteinase genes of these two strains are most probably chromosomally located.