Genetic relationship among gill-infecting Myxobolus species (Myxosporea) of cyprinids: molecular evidence of importance of tissue-specificity

Abstract

The importance of tissue-specificity was studied in Myxobolus spp. infecting the gills of 7 cyprinid species. The 18S rDNA of 10 Myxobolus species was amplified by optimised nested-PCR, resulting in ~1600 bp PCR products. Phylogenetic trees generated by distance matrix and parsimony analyses revealed 4 main groups. Muscle-infecting species all belonged to the same group, while members of 2 gill-infecting groups were clearly distinguishable on the basis of tissue-specificity, and were also recognisable by differences in spore morphology. On the basis of tissue tropism, phylogenetic relationships among the species examined indicate that genetic separation is a more ancient evolutionary feature than host-specificity.KEY WORDS: Myxobolus · Myxosporeans · Phylogeny · 18S rDNA · Tissue tropism · Cyprinids · Gills Resale or republication not permitted without written consent of the publisherDis Aquat Org 58: 35-40, 2004 (2002). Myxobolus species parasitising the gills were also differentiated using a combined polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method by Xiao & Desser (2000) and Eszterbauer et al. (2001). Using this method, Eszterbauer (2002) confirmed that the morphologically indistinguishable M. elegans from orfe and M. hungaricus from common bream are indeed valid species. Furthermore, Eszterbauer et al. (2002) proved that M. pavlovskii is also present in bighead and silver carp.The present paper reports the results of phylogenetic analyses of 10 Myxobolus species infecting the gills of cyprinids in order to determine their genetic relationship and examine the importance of tissuespecificity in the fish hosts. MATERIALS AND METHODS Collection of spores. Myxospores of 10Myxobolus species were collected from 7 fish species in Hungarian natural lakes or rivers and fish farms between 1999 and 2002 (Table 1). After collection and transportation to the laboratory, the 2 to 4 yr old fish were sacrificed using an overdose of the anaesthetic MS 222, followed by severance of the spinal cord.For studying the occurrence of plasmodia in the gills, samples were examined with a stereomicroscope at 10 × magnification. Spores isolated from the plasmodia were carefully examined under coverslip at 100 × magnification with a compound microscope to identify the parasites. Digital pictures of the spore samples were also taken.In most cases, we freed the plasmodia from the host cells or from the capsule formed by the connective tissue of the host under a stereomicroscope, and froze them at -20°C in 1.5 ml centrifuge tubes until further use. The samples contained different numbers of spores (10 2 to 10 6 ). At least 2 different samples of myxospores collected from different fish specimens at different times were used for molecular biological examinations. In the case of Myxobolus bramae, 4 samples of spores were collected from different fish specimens at different times.DNA extraction. After defrosting the spores, samples were centrifuged at low speed (1000 × g). The spores were suspen...

Morphological and molecular characterization of Myxobolus mucosus sp. n. (Myxosporea: Myxobolidae) with basifilamental sporulation in two cyprinid fishes, Rutilus rutilus (L.) and Leuciscus leuciscus (L.) in Russia

“…n. clustered with M. feisti, M. margitae, and M. macrocapsularis and formed an independent clade among cyprinid fish-infecting Myxobolus species but genetically distant from M. basilamellaris. Previous reports showed that genetic separation is a more ancient evolutionary feature than host specificity based on the tissue tropism (Eszterbauer 2004). However, M. feisti develop in a cartilaginous gill ray of the roach surrounding by chondrocytes, M. margitae inside the afferent arteries of the gill filaments of bleak, Alburnus alburnus, and M. macrocapsularis in the filament artery of apical part of the gill filaments of white bream (Molnár 2000;Molnár et al 2008Molnár et al , 2011.…”

“…Most of Myxobolus species of cyprinid fishes select a specific site for their sporulation, and tissue tropism was thought to be one of important taxonomic features (Eszterbauer 2004;Molnár et al 2014). Up to now, more than 260 Myxobolus species have been reported to infect the fish gills (Eiras et al 2005(Eiras et al , 2014.…”

Supplementary studies on Henneguya doneci Schulman, 1962 (Myxozoa: Myxosporea) infecting the gill filaments of Carassius auratus gibelio (Bloch) in China: histologic, ultrastructural, and molecular data

“…Actually, this method always failed to identify the highly similar species that are found in the same tissue and host, which only have subtle differences in spore size and shape. Fortunately, this problem was solved through the molecular approach (Smothers et al 1994;Kent et al 1998;Andree et al 1999;Astrid et al 2004;Eszterbauer 2004). Nowadays, morphologic description of myxozoan species is insufficient.…”

Redescription of Myxobolus pyramidis Chen, 1958(Myxosporea: Bivalvulida)

“…n. (Ali et al 2002); most of these species were reported to infect gills of the host. Exact infection location and tissue tropism are important characters for specific assignment (Molnár 1994;Eszterbauer 2004). M. follius, M. lokiaensis and M. fahmii were noticed to have similar spore shape with M. pyramidis.…”