J. Eukaryot. Microbiol., 54(5), 2007 pp. 418–426
© 2007 The Author(s)
Journal compilation © 2007 by the International Society of Protistologists

Microheterogeneity and Coevolution: An Examination of rDNA Sequence Characteristics in Neoparamoeba pemaquidensis and Its Prokinetoplastid Endosymbiont
CHARLES G. B. CARAGUEL,^a,b CHARLES J. O’KELLY,^c PIERRE LEGENDRE,^d SALVATORE FRASCA Jr.,^e REBECCA J. GAST,^f
BÉATRICE M. DESPRÉS,^a RICHARD J. CAWTHORN ^a,b and SPENCER J. GREENWOOD^a,b
aAVC Lobster Science Centre, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown,
Prince Edward Island, C1A 4P3, Canada, and
^bDepartment of Pathology & Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown,
Prince Edward Island, C1A 4P3, Canada, and
^cBigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine 04575, USA, and
^d De´partement de Sciences Biologiques, Universite´ de Montre´al, C.P. 6128 succursale Centre-ville, Montre´al, QC, H3C 3J7, Canada, and
^e Department of Pathobiology & Veterinary Science, University of Connecticut, Storrs, Connecticut 06269-3089, USA, and
^f Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

Abstract
Neoparamoeba pemaquidensis, the etiological agent of amoebic gill disease, has shown surprising sequence variability among different copies of the 18S ribosomal RNA gene within an isolate. This intra-genomic microheterogeneity was confirmed and extended to an analysis of the internal transcribed spacer (ITS) region. High levels of intra-genomic nucleotide diversity (Pi50.0201– 0.0313) were found among sequenced ITS regions from individual host amoeba isolates. In contrast, the ITS region of its endosymbiont revealed significantly lower levels of intra-genomic nucleotide diversity (Pi50.0028–0.0056) compared with the host N. pemaquidensis. Phylogenetic and ParaFit coevolution analyses involving N. pemaquidensis isolates and their respective endosymbionts confirmed a significant coevolutionary relationship between the two protists. The observation of non-shared microheterogeneity and coevolution emphasizes the complexity of the interactions between N. pemaquidensis and its obligate endosymbiont.

Email: sgreenwood@upei.ca