Genotypic identification and species names in Acanthamoeba: correlation and conflict

Abstract

Many named isolates of Acanthamoeba, e.g. isolates designated Acanthamoeba polyphaga, are used widely in studies of pathogenicity, and other biological characters. However, molecular analyses show that isolates designated A. polyphaga are polyphyletic. Isolates may be very dissimilar at the molecular level, but share a species name, leading investigators to believe that they should share biological characteristics. Here, we present a summary of the correlation in Acanthamoeba between genotypes and the named species of this genus. Analyses of sequences of the nuclear small subunit ribosomal RNA gene (ssu rDNA) have identified at least fifteen genotypes of the free‐living ameba genus Acanthamoeba. Genotype determination has been defined by a sequence dissimilarity of five percent or greater in pairwise sequence comparisons. The ssu rDNA genotypes correlate well with many of the named species of Acanthamoeba. However, in some cases a species name exists as an invalid synonym of other species names within monophyletic genotypic clades. In addition, numerous species names are associated with the large and widely distributed Acanthamoeba genotype T4. Using molecular examination, some of these species designations are shown to be polyphyletic. The genotypes identified by nuclear ssu rDNA are supported by the addition of data from the mitochondrial ssu rDNA, which also provide some resolution of clades within genotype T4. Some lineages within the T4 genotype are associated with named species. Robust identification of Acanthamoeba isolates, including molecular data such as genotypic designation, is required so that data from studies on physiology or pathology may be correctly interpreted.