Molecular genetic diversity and characterization of conjugation genes in the fish parasite Ichthyophthirius multifiliis.
Ichthyophthirius multifiliis is the etiologic agent of "white spot", a commercially important disease of freshwater fish. As a parasitic ciliate, I. multifiliis infects numerous host species across a broad geographic range. Although Ichthyophthirius outbreaks are difficult to control, recent sequencing of the I. multifiliis genome has revealed a number of potential metabolic pathways for therapeutic intervention, along with likely vaccine targets for disease prevention. Nonetheless, major gaps exist in our understanding of both the life cycle and population structure of I. multifiliis in the wild. For example, conjugation has never been described in this species, and it is unclear whether I. multifiliis undergoes sexual reproduction, despite the presence of a germline micronucleus. In addition, no good methods exist to distinguish strains, leaving phylogenetic relationships between geographic isolates completely unresolved. Here, we compared nucleotide sequences of SSUrDNA, mitochondrial NADH dehydrogenase subunit I and cox-1 genes, and 14 somatic SNP sites from nine I. multifiliis isolates obtained from four different states in the US since 1995. The mitochondrial sequences effectively distinguished the isolates from one another and divided them into at least two genetically distinct groups. Furthermore, none of the nine isolates shared the same composition of the 14 somatic SNP sites, suggesting that I. multifiliis undergoes sexual reproduction at some point in its life cycle. Finally, compared to the well-studied free-living ciliates Tetrahymena thermophila and Paramecium tetraurelia, I. multifiliis has lost 38% and 29%, respectively, of 16 experimentally confirmed conjugation-related genes, indicating that mechanistic differences in sexual reproduction are likely to exist between I. multifiliis and other ciliate species.
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Elisabeth
E
MacColl
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Matthew D
MD
Therkelsen
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Tshering
T
Sherpa
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Hannah
H
Ellerbrock
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Lily A
LA
Johnston
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Ravi H
RH
Jariwala
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
WeiShu
W
Chang
Simons Center for Quantitative Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
James
J
Gurtowski
Simons Center for Quantitative Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Michael C
MC
Schatz
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
M
M
Mozammal Hossain
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Donna M
DM
Cassidy-Hanley
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA. Electronic address: tgc3@cornell.edu.
Theodore G
TG
Clark
Department of Biology, Hamilton College, Clinton, NY 13323, USA. Electronic address: wchang@hamilton.edu.
Wei-Jen
WJ
Chang
D000818:Animals; D001499:Bayes Theorem; D004272:DNA, Mitochondrial / Q000235:genetics; D005399:Fishes / Q000469:parasitology*; D016803:Hymenostomatida / Q000145:classification* / Q000235:genetics; D016013:Likelihood Functions; D008957:Models, Genetic; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D012098:Reproduction / Q000235:genetics; D017422:Sequence Analysis, DNA; D014481:United States
D004272:DNA, Mitochondrial
Barcoding; Ciliophora; Hypotrich; IES; Phylogeny; Sexual reproduction