Biodiversity among Lactobacillus helveticus strains isolated from different natural whey starter cultures as revealed by classification trees

Abstract

Lactobacillus helveticus is a homofermentative thermophilic lactic acid bacterium used extensively for manufacturing Swiss type and aged Italian cheese. In this study, the phenotypic and genotypic diversity of strains isolated from different natural dairy starter cultures used for Grana Padano, Parmigiano Reggiano, and Provolone cheeses was investigated by a classification tree technique. A data set was used that consists of 119 L. helveticus strains, each of which was studied for its physiological characters, as well as surface protein profiles and hybridization with a species-specific DNA probe. The methodology employed in this work allowed the strains to be grouped into terminal nodes without difficult and subjective interpretation. In particular, good discrimination was obtained between L. helveticus strains isolated, respectively, from Grana Padano and from Provolone natural whey starter cultures. The method used in this work allowed identification of the main characteristics that permit discrimination of biotypes. In order to understand what kind of genes could code for phenotypes of technological relevance, evidence that specific DNA sequences are present only in particular biotypes may be of great interest.

FIG.1.

Dendrogram based on the UPGMA clustering of the Pearson association coefficient of RFLP patterns obtained after hybridization of the internal PCR-amplified 388-bp fragment of IS1201 with total genomic DNA from all 119 L. helveticus strains following restriction with EcoRI. The scale at the top right shows the Pearson correlation from 0 to 100% (RFLP insertion sequence).

FIG. 2.

Classification tree. Term., terminal.