Arrested development of the myxozoan parasite, Myxobolus cerebralis, in certain populations of mitochondrial 16S lineage III Tubifex tubifex

Abstract

Laboratory populations of Tubifex tubifex from mitochondrial (mt)16S ribosomal DNA (rDNA) lineage III were generated from single cocoons of adult worms releasing the triactinomyxon stages (TAMs) of the myxozoan parasite, Myxobolus cerebralis. Subsequent worm populations from these cocoons, referred to as clonal lines, were tested for susceptibility to infection with the myxospore stages of M. cerebralis. Development and release of TAMs occurred in five clonal lines, while four clonal lines showed immature parasitic forms that were not expelled from the worm (non-TAM producers). Oligochaetes from TAM- and non-TAM-producing clonal lines were confirmed as lineage III based on mt16S rDNA and internal transcribed spacer region 1 (ITS1) sequences, but these genes did not differentiate these phenotypes. In contrast, random amplified polymorphic DNA analyses of genomic DNA demonstrated unique banding patterns that distinguished the phenotypes. Cohabitation of parasite-exposed TAM- and non-TAM-producing phenotypes showed an overall decrease in expected TAM production compared to the same exposure dose of the TAM-producing phenotype without cohabitation. These studies suggest that differences in susceptibility to parasite infection can occur in genetically similar T. tubifex populations, and their coexistence may affect overall M. cerebralis production, a factor that may influence the severity of whirling disease in wild trout populations.

Prevalence of Myxobolus cerebralis Infections Among Genetic Lineages of Tubifex tubifex at Three Locations in the Madison River, Montana

“…In laboratory experiments using worms collected from California, Montana, Utah, and Argentina, Rasmussen et al (2008) observed higher Lineage III susceptibility in comparison to Lineage I. In comparison, Beauchamp et al (2002) found variation between 2 locations of the Colorado River, Colorado.…”

“…There are multiple genetic lineages (I-VI) of T. tubifex (Sturmbauer et al, 1999;Beauchamp et al, 2001;Crottini et al, 2008) that can be distinguished with the use of mitochondrial (16S) and genomic (18S and ITS) DNA sequences. Susceptibility of T. tubifex lineages to infection by the myxospores of M. cerebralis ranges from highly susceptible (Lineage III) and moderately susceptible (Lineage I), to completely resistant (Lineages V and VI; Stevens et al, 2001;Beauchamp et al, 2002;Steinbach et al, 2006;Arsan et al, 2007;Rasmussen et al, 2008). Although much of the work identifying genetic lineages of T. tubifex is based on the mitochondrial 16S rDNA gene, it is unlikely that this gene directly confers resistance to the parasite (Arsan et al, 2007).…”

“…Variation within lineages has also been documented (Beauchamp et al, 2002;Arsan et al, 2007;Rasmussen et al, 2008). Previous assessment of parasitic infection in T. tubifex has been done by observing TAM production (Beauchamp et al, 2002;Kerans et al, 2004Kerans et al, , 2005Rasmussen et al, 2008;Hallett et al, 2009) and by diagnostic PCR originally developed for fish and later used in T. tubifex (Gilbert and Granath, 2001). More recently, qPCR was used to detect the presence of M. cerebralis in T. tubifex (Arsan et al, 2007).…”

“…More recently, qPCR was used to detect the presence of M. cerebralis in T. tubifex (Arsan et al, 2007). In addition, many studies (Gilbert and Granath, 2001;DuBey and Caldwell, 2004;Koel et al, 2006;Arsan et al, 2007;Baxa et al, 2008;Hallett et al, 2009;Granath and Vincent, 2010) used M. cerebralis diagnostic PCR to confirm infection in worms, which had been visually identified as TAM producers.…”

Correlation of environmental attributes with histopathology of native Yellowstone cutthroat trout naturally infected with Myxobolus cerebralis

“…M. cerebralis was detected in Yellowstone Lake in 1998 and over the last decade has posed a growing threat on the declining cutthroat trout population (Koel et al 2005, 2006. The Yellowstone Lake ecosystem is the last stronghold for one of the most ecologically and economically valued inland cutthroat trout populations in North America.We examined Yellowstone cutthroat trout exposed at 4 different times in 3 sites of a Myxobolus cerebralispositive tributary to Yellowstone Lake: Pelican Creek Baxa et al 2008) and abundance of infected T. tubifex to be relatively uniform (J. Alexander, Montana State University, pers. comm.).…”