Remarks on the validity of Myxobolus ampullicapsulatus and Myxobolus honghuensis (Myxozoa: Myxosporea) based on SSU rDNA sequences

Abstract

In the present study, we isolated three populations of Myxobolus ampullicapsulatus from the gills of crucian carp, Carassius auratus auratus, two from Yongchuan, Chongqing area and one from Poyang Lake, Jiangxi area, China, sequenced their complete small subunit ribosome RNA gene, analyzed their genetic distance and gene similarity, and explored their relationship based on Bayesian inference and maximum likelihood analyses of their small subunit ribosomal DNA. The results combined with their morphological characteristics suggest that M. ampullicapsulatus infecting the gills and pharynx of allogynogenetic gibel carp, Carassius auratus gibelio, should be Myxobolus honghuensis. This study highlights the importance of DNA sequence comparisons for distinguishing Myxobolus species and indicates that the intra-species identification for the two Myxobolus species mentioned in the present research should be less than ten variation sites. In morphology, M. honghuensis Liu et al. (2012) parasitic on the gills of C. auratus auratus (goldfish) was collected from Chongqing area, and its mature spore was 16.5-19.5 × 8.5-10.0 μm in size, polar capsule was 7.0-10.0 × 2.5-4.0 μm in size, and polar filament had 9-10 coils. M. honghuensis Liu et al. (2012) isolated from the pharynx of C. auratus gibelio was sampled in Hubei area, and its mature spore was 15.1-19.5 × 9.0-11.3 μm in size, polar capsule was 7.9-8.1 × 3.0-4.5 μm in size, and polar filament had 7-8 coils.

Fig. 1

Comparison of spores among the populations of M. ampullicapsulatus and M. honghuensis morphologically. a M. ampullicapsulatus CQLg (from Zhao et al. 2008). b M. ampullicapsulatus CQ collected in the present study. c M. ampullicapsulatus JXa.a collected in the present study. d M. ampullicapsulatus JSa.g (from Xi et al. 2011). e M. honghuensis HBa.g (from Liu et al. 2012). Bar = 10 μm

Fig. 2

Regions of alignment of SSU rRNA gene sequences of populations of M. ampullicapsulatus and M. honghuensis. Regions are separated by vertical lines and the reference sequence. Insertions and deletions were compensated by introducing alignment gaps (dash). Matched sites are represented by dots. Distinct sequence signatures of each clade are shaded

Fig. 3

Phylogenetic tree generated by maximum likelihood analysis of the aligned small subunit ribosomal RNA gene sequences. Nodal supports are indicated for bootstrap confidence values resulting from ML and posterior probability of Bayesian analysis. “-” reflects minor differences between maximum likelihood and other methods. GenBank accession numbers for each taxon are listed. The distance scale is shown under the tree. Schematic of (a) M. ampullicapsulatus and (b) M. honghuensis. Bar = 10 m