Notes on the Phylogenetic Background to Lactobacillus Taxonomy

Speculations about the phylogeny and natural relationships of and within the genus Lactobacillus are made, based upon current taxonomic knowledge. Phylogenetic speculation has long held a fascination for biologists who interest themselves in taxonomy and it remains to be seen whether the recent invasion of this field by computers will render this fascination fatal. The present notes are an attempt to extend certain speculations which occur in the literature. For example Davis (1955) suggested that the difficulty found in differentiating species of hetero-fermentative lactobacilli (see Rogosa & Sharpe, 1959; Cheeseman & Berridge, 1959) might indicate that these organisms are of more recent origin than the homo-fermenters and might be derived from them. De Ley (1962) stated ‘one can thus imagine that the “ heterolactic ” (i.e. heterofermentative) bacteria could phylo-genetically be derived from the “ homolactic ” (i.e. homofermentative) bacteria by the loss of aldolase and transketolase’. Lactobacilli have been much studied and the taxonomy is comparatively well