The role of genotype and phenotype in the infraspecific taxonomy of Lactobacillus species.

Data recently obtained for two infraspecific groups within the species Lactobacillus delbrueckii and Lactobacillus plantarum led to the description of two novel subspecies: Lactobacillus delbrueckii subsp. indicus (Dellaglio et al., 2005) and Lactobacillus plantarum subsp. argentoratensis (Bringel et al., in press), respectively. Subspecies are the lowest taxonomic ranks with standing in nomenclature and are based on the recognition of phenotypic and/or genotypic heterogeneities (Rosselló-Mora & Amann, 2001). The descriptions of the aforementioned subspecies were the result of a polyphasic approach. It allowed to highlight that, in both species, the genotypic/genomic diversity was more marked than the phenotypic one. Moreover, in the case of L. delbrueckii, the phenotypic similarity between two subspecies was due to a phenomenon of convergent evolution: two different genetic equipments were responsible of the same phenotypic manifestation (Germond et al., 2003). On the basis of those results, we present some considerations on the contribution that phenotypic and genotypic/genomic data may give to the delineation of subspecies. The experimental results presented make us suggest that prominent role in infraspecific taxonomy should be given to genotype since laboratory conditions could be misleading in the evaluation of “in vivo” expressed traits (phenotype) and, most of all, genotypic/genomic analysis is fundamental to understand which potentialities an organism could express.