Most of the lactic acid bacteria (LAB) are able to grow in milk mainly due to the activity of a complex and well-developed proteolytic system. Cell envelope-associated proteinases (CEPs) begin casein hydrolysis and allow for releasing the peptides, enclosed in the structure of native milk proteins that are essential for growth of Lactobacillus helveticus. The biodiversity of genes encoding CEPs among L. helveticus strains can have an effect on some technological parameters such as acid production, bacterial growth rate in milk as well as liberation of biologically active peptides. The study reveals significant differences in the presence of various variants of CEPs encoding genes among ten novel Polish strains and indicates the intraspecific diversity exhibited by L. helveticus. In terms of distribution of CEPs genes, four different genetic profiles were found among the microorganisms analyzed. Furthermore, the strains exhibited also various levels of proteolytic activity. Molecular analysis revealed that prtH3 is the most abundant CEPs-encoding gene among the strains investigated. The results indicate also that ecological niche and environmental conditions might affect proteolytic properties of L. helveticus strains. The greatest variety in terms of quantity of the detected CEP encoding genes was noticed in L. helveticus 141, T105 and T104 strains. In these strains, the combination of three nucleotide gene sequences (prtH/prtH2/prtH3) was identified. Interestingly, T104 and T105 exhibited the highest proteolytic activity and also the fastest dynamic of milk acidification among the tested strains of L. helveticus.
Keywords: Lactobacillus helveticus; cell envelope proteinases (CEPs); proteolytic activity.