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Reevaluation of the Phylogenetic Relationship Between Mobilid and Sessilid Peritrichs (Ciliophora, Oligohymenophorea) Based on Small Subunit Rrna Genes Sequences

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Reevaluation of the Phylogenetic Relationship Between Mobilid and Sessilid Peritrichs (Ciliophora, Oligohymenophorea) Based on Small Subunit Rrna Genes Sequences View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Institute of Hydrobiology, Chinese Academy Of Sciences J. Eukaryot. Microbiol., 53(5), 2006 pp. 397–403 r 2006 The Author(s) Journal compilation r 2006 by the International Society of Protistologists DOI: 10.1111/j.1550-7408.2006.00121.x Reevaluation of the Phylogenetic Relationship between Mobilid and Sessilid Peritrichs (Ciliophora, Oligohymenophorea) Based on Small Subunit rRNA Genes Sequences YING-CHUN GONG,a,b YU-HE YU,a EDUARDO VILLALOBO,c FEI-YUN ZHUa and WEI MIAOa aLaboratory of Taxonomy and Ecology of Protozoa, Institute of Hydrobiology, The Chinese Academy of Sciences, Wuhan 430072, China, and bGraduate School of the Chinese Academy of Sciences, Beijing 100039, China, and cDepartamento de Microbiologia, Facultad de Biologia, Universidad de Sevilla, Sevilla 41012, Spain ABSTRACT. Based on morphological characters, peritrich ciliates (Class Olygohymenophorea, Subclass Peritrichia) have been sub- divided into the Orders Sessilida and Mobilida. Molecular phylogenetic studies on peritrichs have been restricted to members of the Order Sessilida. In order to shed more light into the evolutionary relationships within peritrichs, the complete small subunit rRNA (SSU rRNA) sequences of four mobilid species, Trichodina nobilis, Trichodina heterodentata, Trichodina reticulata, and Trichodinella myakkae were used to construct phylogenetic trees using maximum parsimony, neighbor joining, and Bayesian analyses. Whatever phylogenetic method used, the peritrichs did not constitute a monophyletic group: mobilid and sessilid species did not cluster together. Similarity in morphology but difference in molecular data led us to suggest that the oral structures of peritrichs are the result of evolutionary convergence. In addition, Trichodina reticulata,aTrichodina species with granules in the center of the adhesive disc, branched separately from its con- geners, Trichodina nobilis and Trichodina heterodentata, trichodinids without such granules. This indicates that granules in the adhesive disc might be a phylogenetic character of high importance within the Family Trichodinidae. Key Words. Adhesive disc, granule, Mobilida, phylogeny, SSrRNA, Trichodina, Trichodinella. ERITRICH ciliates (Ciliophora, Oligohymenophorea), Subclass Peritrichia. Four mobilid species, and three different P characterized by possession of an expanded oral area, the phylogenetic methodologies, namely maximum parsimony peristome, and encircled by two prominent bands of cilia that run (MP), neighbor joining (NJ), and Bayesian analysis were includ- in counterclockwise fashion, have been long recognized as a high- ed in this study. er taxon among ciliates (Corliss 1968). The Subclass Peritrichia is traditionally subdivided into two Orders based on the mode of MATERIALS AND METHODS attachment: the Order Sessilida (Kahl 1933) includes mostly ses- sile representatives having a scopula as a substrate-attaching Samples collection, isolation, and identification. Samples organ, while the Order Mobilida (Kahl 1933) includes mostly free- were collected from different fish hatcheries in Wuhan, Hubei swimming forms, although parasitic form representatives have Province, China (Table 1). Fishes with symptoms of serious in- an aboral adhesive disc as a substrate-attaching organ. fections were taken and trichodinids present in different organs Most species of the Order Mobilida, hereafter referred as mobi- were isolated using glass micropipettes under a dissecting micro- lids, occur epizootically on various freshwater and marine hosts. scope. Organisms were selected by their dimensions, body shape, More than 280 mobilid species have been reported to infect the characteristic movement, and location on the host. Every speci- skin, gills, and urinary bladders of fishes and amphibians and in- men was washed three times by double-distilled and autoclave- tegument of a few invertebrates (Beers 1964; Van As and Basson sterilized water to assure no contaminants were carried over. 1989; Xu 1999). These peritrichs have been implicated in severe Specimens were stained by silver nitrate, using a modification disease and mortalities of fish, causing many economic losses in of Klein’s technique, as described by Lom (1958) and Wellborn various parts of the world (Van As and Basson 1987; Van As and (1967). The main structural character used to classify mobilid Viljoen 1984). Despite their economic and ecological importance, peritrichs is the precise structure of the adhesive disc (Basson mobilid peritrichs, represented by Trichodina and Urceolaria, and Van As 1989; Beers 1964). The specimens were identified remain less studied than their close-relatives, sessilid peritrichs, after visualization in a Zeiss Axioplan microscope (Carl Zeiss, represented by Vorticella and Epistylis. For instance, only sessilid Hallberg-moos, Germany) and comparison with published de- peritrichs with molecular markers have been included in studies of scriptions (Basson and Van As 1993; Chen 1963; Duncan 1977; evolutionary relationships within the Class Oligohymenophorea Hirschman and Partsch 1955; Mueller 1937). (Greenwood, Sogin, and Lynn 1991b; Miao, Yu, and Shen 2001; Sampling is an important factor affecting consistency of phylo- Miao et al. 2004). Morphological characters, such as the pattern of gentic analyses. We aimed at analyzing as many species as pos- ciliary organelles in the oral area and the shape of denticles in the sible, but because culturing trichodinid ciliates is not possible we adhesive disc, have been used tentatively to study the systematics relied on harvesting individuals to obtain DNA. In the light of of the families Urceolariidae and Trichodinidae of the Order these drawbacks, we selected for further work those species that Mobilida (Gong et al. 2005; Raabe 1963; Xu et al. 2000), but seemed to establish monospecific infections, namely Trichodina these characters have proved inadequate to reconstruct evolution- heterodentata (Duncan 1977), Trichodina nobilis (Chen 1963), ary history as they are unique features of this order of ciliates and Trichodina reticulata (Hirschman and Partsch 1955), and Tricho- their weighting is difficult to determine. This led us to search for dinella myakkae (Mueller 1937). other characters that could be useful for phylogenetic analysis, DNA extraction. For each species, about 100 individuals were such as the small subunit (SSU) rRNA gene sequence, to deter- harvested, suspended in lysis buffer (10 mM Tris-HCl, pH 8.0; mine the phylogenetic relationship of mobilids within the 1 M EDTA, pH 8.0; 0.5% sodium dodecyl sulfate [w/v]; 60 mg/ml proteinase K), and incubated at 55 1C for 12–20 h. DNA was Corresponding Author: Y.-H. Yu, Laboratory of Taxonomy and Ecol- extracted using a standard phenol/chloroform method, precipitat- ogy of Protozoa, Institute of Hydrobiology, The Chinese Academy of ed with ethanol, and resuspended in TE buffer (10 mM Tris- Sciences, Wuhan, 430072, People’s Republic of China—Telephone HCl, pH 8.0; 1 mM EDTA, pH 8.0; Sambrook, Fritsch, and number: 0086-27-68780773; FAX number: 0086-27-68780773; e-mail: Maniatis 1989). Polymerase chain reaction (PCR) amplifications [email protected] were carried out in 25- ml vol. reactions containing 50 ng of 397 398 J. EUKARYOT. MICROBIOL., VOL. 53, NO. 5, SEPTEMBER– OCTOBER 2006 Table 1. List of trichodinids used in this paper including name of species and host species, and the place, and year of isolation. Species Host species Origin Isolator, Year Trichodinella heterodentata Ctenopharynodon idella Guanqiao hatchery F.Y. Zhu, 2001 Trichodinella nobilis Hypophthalmichtys molitrix Hanyang hatchery Y.C. Gong, 2004 Trichodinella reticulata Ctenopharynodon idella Haogou hatchery Y.C. Gong, 2004 Trichodinella myakkae Ctenopharynodon idella Hanyang hatchery F.Y. Zhu, 2001 template DNA, 1 mM of both forward and reverse primers (F: 50- Phylogenetic analysis. Multiple sequence alignment was per- AACCTGGTTGATCCTGCCAGT-30;R:50-TGATCCTTCTG- formed using ClustalX (Thompson et al. 1997). Considering sec- CAGGTTCACCTAC-30) (Medlin et al. 1988), 0.2 mM dNTP, ondary structural features of the SSrRNA molecule, we further 2 mM MgCl2, and 1 U of Taq DNA polymerase (Fermentas, Fos- refined the alignment by removing hypervariable regions of he- ter City, CA). Temperature cycling was five cycles of denaturation lixes E23_1 and E23_2 with the DCSE (Dedicated Comparative for 1 min at 94 1C, primer annealing for 2 min at 56 1C, and ex- Sequence Editor; De Rijk and De Wachter 1993). MP (Farris tension for 2 min at 72 1C, followed by 35 cycles in the same 1970) and NJ (Saitou and Nei 1987) analyses were performed with manner, but with the annealing temperature increased to 62 1C. PAUP 4.0b10 (Swofford 2002), and Bayesian analysis (Mau PCR amplifications were performed in a Perkin-Elmer GeneAmp 1996; Rannala and Yang 1996) was carried out with MrBayes PCR System 9600 (PE Applied Biosystems, Mississauga, ON, 3.0b (Huelsenbeck and Ronquist 2001). For MP analysis, charac- Canada). ters were not weighted. Tree searches used tree bisection- PCR products were purified using the Biostar Glassmilk DNA reconnection (TBR) branch swapping and 1,000 simple sequence Purification Kit (BioStar International, Toronto, ON, Canada) fol- addition replicates. For NJ and Bayesian analyses, the tree top- lowing supplier’s instructions. Ligation reactions were performed ologies were inferred using the model ‘‘GTR1I1G,’’ which was overnight at 4 1C in 10-ml reaction mixtures containing
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