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. 2016 Oct 29;1(1):797–798. doi: 10.1080/23802359.2016.1197076

The complete mitochondrial genome of Acanthosentis cheni (Acanthocephala: Quadrigyridae)

Rui Song a, Dong Zhang b, Shiming Deng a, Deming Ding a, Fuchu Liao a,✉, Lusha Liu c
PMCID: PMC7799462  PMID: 33473631

Abstract

Acanthosentis cheni is a marine or brackish acanthocephalan found in fish. The complete mitochondrial genome of A. cheni (Acanthocephala: Quadrigyridae) is first sequenced. It is a circular molecule of 13,695 bp in size and consists of 12 protein-coding genes (PCGs), 20 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes. Except tRNA-Gln, all other mitochondrial genes were encoded on the heavy strand. The gene order and orientation of A. cheni mitogenome are basically identical to that of other acanthocephala. This study will facilitate the further research of the population genetics of this species and systematic analyses of the acanthocephala.

Keywords: Acanthosentis cheni, mitogenomics, parasite, phylogeny

Acanthosentis cheni is a marine or brackish acanthocephalan found in fish. The complete mitochondrial genome of A. cheni (Acanthocephala: Quadrigyridae) is first sequenced. It is a circular molecule of 13,695 bp in size and consists of 12 protein-coding genes (PCGs), 20 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes. Except tRNA-Gln, all other mitochondrial genes were encoded on the heavy strand. The gene order and orientation of A. cheni mitogenome are basically identical to that of other acanthocephala. This study will facilitate the further research of the population genetics of this species and systematic analyses of the acanthocephala.

Acanthocephalans (thorny headed worms), which use vertebrates as definitive hosts and arthropods as intermediate hosts, are a small group of obligate endoparasites with a total of about 1200 species in the world (Kennedy 2006). Acanthosentis cheni is a marine or brackish acanthocephalan found in the anadromous fish Coilia nasus (Li et al. 2011). Despite the osmotic pressure is rather stable in the stomach and intestine of fish, it is difficult for endoparasites to survive for a long time in an environment of increased or decreased salinity (Möller 1978). However, Song et al. (2014) confirmed the samples from marine, brackish and fresh water are the same parasite A. cheni using the ITS gene. Here, the complete mitogenome of this species was first determined. A. cheni was dissected out under a microscope from intestines of C. nasus from Dongting Lake in Yueyang, Hunan province of China, with voucher number ACCN20160122. The accurate annotated mitochondrial genome sequence was submitted to GenBank with accession number KX108947.

The complete mtDNA is 13,695 bp in length and contains 12 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, which is similar to that of other acanthocephala (Gazi et al. 2012), but with only 20 transfer RNA (tRNA) genes while generally there are 22 tRNA in other acanthocephala (Gazi et al. 2012; Pan & Nie 2013; Gazi et al. 2016). The base composition of the complete mitochondrial genome was A (22.38%), C (10.01%), G (24.74%), T (42.87%), with an obvious AT bias (65.25%), as generally shown in other acanthocephalans’ mitogenomes (Gazi et al. 2012; Pan & Nie 2013; Gazi et al. 2016). Except tRNA-Gln, all other mitochondrial genes were encoded on the heavy strand (H-strand). Six PCGs, COX1, ND6, ND3, Cytb, COX2 and ND2 start with GTG. Three other PCGs, NAD4L, ND4 and ND1 start with ATT, ND5 and COX3 with ATA, while ATP6 with ATG as start codon. Six genes use complete stop codons, including four genes with TAG (ND6, ND3, NAD4L and ND1), two with TAG (ATP6 and Cytb), whereas other six genes appear to end incomplete stop codons with T (COX1, ND4, ND5, COX2, COX3, and ND2). In 12 PCGs, the shortest one is NAD4L gene (249 bp) and the longest one is ND5 (1,549 bp). The tRNAscan algorithm detected only two tRNA genes within the complete mitochondrial genome sequence. Additional putative tRNA genes were detected by searching by eye for the anticodon sequences and surrounding sequences for secondary structure. The 20 tRNA genes with the size ranging from 51 bp to 72 bp are interspersed along the whole genome. The sequence length of the rrnL and rrnS rRNA is 876 and 591 bp, respectively. The total length of the non-coding region (NCR) for A. cheni is 1,209 bp, which is composed of nine intergenic spacer sequences, ranging from 16 to 711 bp.

Based on the nine published mitogenome sequences of acanthocephala and an outgroup of Rotatoria Philodina citrine, a phylogenetic tree (Figure 1) was constructed using MEGA 6.0 (Tamura et al. 2013). Mitochondrial genome analyses based on MP, ML and NJ yielded identical phylogenetic trees, indicating a close phylogenetic affinity of nine species of acanthocephala and P. citrine (Figure 1). It appeared A. cheni, Hebesoma violentum, Pallisentis celatus which from Eoacanthocephala and Polyacanthorhynchus caballeroi formed a monophyletic group with the high bootstrap value (100%). The present study will facilitate the further research of the population genetics of this species and systematic analyses of the acanthocephala.

Figure 1.

Figure 1.

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Phylogenetic tree generated using the NJ method based on 12 protein-coding genes for nine acanthocephala and one Rotatoria. Acanthosentis cheni (KX108947), Southwellina hispida (NC_026516.1), Pallisentis celatus (NC_022921.1), Oncicola luehei (NC_016754.1), Plagiorhynchus transverses (NC_029767.1), Polyacanthorhynchus caballeroi (NC_029766.1), Centrorhynchus aluconis (NC_029765.1), Leptorhynchoides thecatus (NC_006892.1), Hebesoma violentum (KC415004.1) and Philodina citrine (NC_019806.1).

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Funding information

This study was supported by the Earmarked Fund for China Agriculture Research System (No. CARS-46-41) and Important Research Project of Hunan Provincial Science and Technology Department (2015NK3060).

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