Molecular Biology and Evolution, Vol 16, 1135-1144, Copyright © 1999 by Society for Molecular Biology and Evolution
PT Monis, RH Andrews, G Mayrhofer and PL Ey
The long-standing controversy regarding whether Giardia intestinalis is a
single species prevalent in both human and animal hosts or a species
complex consisting of morphologically similar organisms that differ in host
range and other biotypic characteristics is an issue with important
medical, veterinary, and environmental management implications. In the past
decade, highly distinct genotypes (some apparently confined to particular
host groups) have been identified by genetic analysis of samples isolated
from different host species. The aim of this study was to undertake a
phylogenetic analysis of G. intestinalis that were representative of all
known major genetic groups and compare them with other Giardia species,
viz. G. ardeae, G. muris, and G. microti. Segments from four "housekeeping"
genes (specifying glutamate dehydrogenase, triose phosphate isomerase,
elongation factor 1 alpha, and 18S ribosomal RNA) were examined by analysis
of 0.48-0.69- kb nucleotide sequences determined from DNA amplified in
polymerase chain reactions from each locus. In addition, isolates were
compared by allozymic analysis of electrophoretic data obtained for 21
enzymes representing 23 gene loci. The results obtained from these
independent techniques and different loci were essentially congruous.
Analyses using G. ardeae and/or G. muris as outgroups supported the
monophyly of G. intestinalis and also showed that this species includes
genotypes that represent at least seven deeply rooted lineages, herein
designated assemblages A-G. Inclusion of G. microti in the analysis of 18S
rRNA sequence data demonstrated the monophyly of Giardia with the same
median body morphology but did not support the monophyly of G.
intestinalis, instead placing G. microti within G. intestinalis. The
findings support the hypothesis that G. intestinalis is a species complex
and suggest that G. microti is a member of this complex.
ORIGINAL ARTICLE
Molecular systematics of the parasitic protozoan Giardia intestinalis
Department of Microbiology and Immunology, University of Adelaide, Australia. paul.monis@sawater.sa.gov.au
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