The Evolutionary History of the Genus Acanthamoeba and the Identification of Eight New 18S rRNA Gene Sequence Types

Authors

  • Diane R. Stothard,

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    • 1

      Current Address: Department of Medicine. Division of Infectious Diseases, Indiana University School of Medicine, 435 Emerson Hall, 545 Barnhill Drive. Indianapolis. IN 46202. USA.

  • Jill M. Schroeder-Diedrich,

    1. Department of Molecular Genetics, The Ohio State University. Columbus. Ohio 43210-1292, USA
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  • Mohammad H. Awwad,

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    • 2

      Current Address: Department of Zoology. Faculty of Science, Benha Branch, University of Zagazig. Egypt.

  • Rebecca J. Gast,

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    • 3

      Current Address: Department of Biology, Woods Hole Oceanography Institution. 324 Redfield Building. Woods Hole, MA 02543, USA.

  • Dolena R. Ledee,

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    • 4

      Current Address: Department of Ophthalmology, University of Pennsylvania, Stellar Chance Labs, 422 Curie Boulevard, Philadelphia, PA 19104, USA.

  • Salvador Rodriguez-Zaragoza,

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    • 5

      Current Address: Laboratory of Microbial Ecology, UIICSE. Universidad Nacional Autónoma de Mexico. Campus Iztacala, Apartado Postal 16-491 Azcapotzalco. Déistrio Federal, Código Postal 02011, Mexico.

  • Chantal L. Dean,

    1. Department of Molecular Genetics, The Ohio State University. Columbus. Ohio 43210-1292, USA
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  • Paul A. Fuerst,

    1. Department of Molecular Genetics, The Ohio State University. Columbus. Ohio 43210-1292, USA
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  • Thomas J. Byers

    Corresponding author
      To whom correspondence should be addressed. Telephone: 614-292-5963; Fax: 614-292-4466: Email: byers.2@osu.edu
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To whom correspondence should be addressed. Telephone: 614-292-5963; Fax: 614-292-4466: Email: byers.2@osu.edu

Abstract

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.

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