Current Address: Department of Medicine. Division of Infectious Diseases, Indiana University School of Medicine, 435 Emerson Hall, 545 Barnhill Drive. Indianapolis. IN 46202. USA.
The Evolutionary History of the Genus Acanthamoeba and the Identification of Eight New 18S rRNA Gene Sequence Types
Article first published online: 2 MAY 2007
Journal of Eukaryotic Microbiology
Volume 45, Issue 1, pages 45–54, January 1998
How to Cite
Stothard, D. R., Schroeder-Diedrich, J. M., Awwad, M. H., Gast, R. J., Ledee, D. R., Rodriguez-Zaragoza, S., Dean, C. L., Fuerst, P. A. and Byers, T. J. (1998), The Evolutionary History of the Genus Acanthamoeba and the Identification of Eight New 18S rRNA Gene Sequence Types. Journal of Eukaryotic Microbiology, 45: 45–54. doi: 10.1111/j.1550-7408.1998.tb05068.x
- Issue published online: 2 MAY 2007
- Article first published online: 2 MAY 2007
- Received 3-17-97. 8-25-97; accepted 8-25-97
- granulomatous amoebic encephalitis;
- multiple rDNA alleles;
- opportunistic pathogen;
ABSTRACT The 18S rRNA gene (Rns) phylogeny of Acanthamoeba is being investigated as a basis for improvements in the nomenclature and taxonomy of the genus. We previously analyzed Rns sequences from 18 isolates from morphological groups 2 and 3 and found that they fell into four distinct evolutionary lineages we called sequence types T1-T4. Here, we analyzed sequences from 53 isolates representing 16 species and including 35 new strains. Eight additional lineages (sequence types T5-T12) were identified. Four of the 12 sequence types included strains from more than one nominal species. Thus, sequence types could be equated with species in some cases or with complexes of closely related species in others. The largest complex, sequence type T4, which contained six closely related nominal species, included 24 of 25 keratitis isolates. Rns sequence variation was insufficient for full phylogenetic resolution of branching orders within this complex, but the mixing of species observed at terminal nodes confirmed that traditional classification of isolates has been inconsistent. One solution to this problem would be to equate sequence types and single species. Alternatively, additional molecular information will be required to reliably differentiate species within the complexes. Three sequence types of morphological group 1 species represented the earliest divergence in the history of the genus and, based on their genetic distinctiveness, are candidates for reclassification as one or more novel genera.