The complete mitochondrial genome sequence ofEimeria magna(Apicomplexa: Coccidia)

The Complete Mitochondrial Genome Sequence of Eimeria kongi (Apicomplexa: Coccidia)

Rabbit coccidiosis is caused by infection with one or, more commonly, several Eimeria species that parasitize the hepatobiliary ducts or intestinal epithelium of rabbits. Currently, there are eleven internationally recognized species of rabbit coccidia, with the complete mitochondrial (mt) genomes of six species commonly infecting rabbits having been sequenced and annotated. Eimeria kongi was initially discovered in 2011 and prompted a preliminary study on this species. Through traditional morphological analysis, E. kongi was identified as a novel species of rabbit coccidia. To further validate this classification, we sequenced and annotated its mitochondrial genome. The complete mt genome of E. kongi spans 6258 bp and comprises three cytochrome genes (cytb, cox1, cox3), fourteen gene fragments for the large subunit (LSU) rRNA, and nine gene fragments for the small subunit (SSU) rRNA, lacking transfer RNA (tRNA) genes. Moreover, phylogenetic analysis of the mitochondrial genome sequence of E. kongi revealed its clustering with six other species of rabbit coccidia into a monophyletic group. Additionally, E. irresidua and E. flavescens were grouped within the lineage lacking oocyst residuum, consistent with their morphological characteristics. Consistent with multiple molecular phylogenies, in this investigation, E. kongi was further confirmed as a new species of rabbit coccidia. Our research findings are of great significance for the classification of coccidia and for coccidiosis prevention and control in rabbits.

Eimeria zuernii (Eimeriidae: Coccidia): mitochondrial genome and genetic diversity in the Chinese yak

BACKGROUND

Coccidiosis caused by Eimeria zuernii (Eimeriidae: Coccidia) represents a significant economic threat to the bovine industry. Understanding the evolutionary and genetic biology of E. zuernii can assist in new interaction developments for the prevention and control of this protozoosis.

METHODS

We defined the evolutionary and genetic characteristics of E. zuernii by sequencing the complete mitogenome and analyzing the genetic diversity and population structure of 51 isolates collected from eight yak breeding parks in China.

RESULTS

The 6176-bp mitogenome of E. zuernii was linear and encoded typical mitochondrial contents of apicomplexan parasites, including three protein-coding genes [PCGs; cytochrome c oxidase subunits I and III (cox1 and cox3), and cytochrome b (cytb)], seven fragmented small subunit (SSU) and 12 fragmented large subunit (LSU) rRNAs. Genome-wide comparative and evolutionary analyses showed cytb and cox3 to be the most and least conserved Eimeria PCGs, respectively, and placed E. zuernii more closely related to Eimeria mephitidis than other Eimeria species. Furthermore, cox1-based genetic structure defined 24 haplotypes of E. zuernii with high haplotype diversities and low nucleotide diversities across eight geographic populations, supporting a low genetic structure and rapid evolutionary rate as well as a previous expansion event among E. zuernii populations.

CONCLUSIONS

To our knowledge, this is the first study presenting the phylogeny, genetic diversity, and population structure of the yak E. zuernii, and such information, together with its mitogenomic data, should contribute to a better understanding of the genetic and evolutionary biological studies of apicomplexan parasites in bovines.

Transcriptome mining of RNA viruses (family Totiviridae ) in Eimeria necatrix and Eimeria stiedai

Coccidian protozoa from the genus Eimeria are widespread parasites of vertebrates, causing serious disease (coccidiosis) and economic loss most notably in poultry. Several species of Eimeria are themselves infected with small RNA viruses assigned to the family Totiviridae . In this study, the sequences of two such viruses were newly determined, one of which represents the first complete protein-coding sequence of a virus from E. necatrix , an important pathogen of chickens, and the other of which is from E. stiedai , an important pathogen of rabbits. Sequence features of the newly identified viruses, compared with those of ones reported previously, provide several insights. Phylogenetic analyses suggest that these eimerian viruses constitute a well-demarcated clade, probably deserving of recognition as a distinct genus.

Nematode chromosomes

The nematode Caenorhabditis elegans has shed light on many aspects of eukaryotic biology, including genetics, development, cell biology, and genomics. A major factor in the success of C. elegans as a model organism has been the availability, since the late 1990s, of an essentially gap-free and well-annotated nuclear genome sequence, divided among 6 chromosomes. In this review, we discuss the structure, function, and biology of C. elegans chromosomes and then provide a general perspective on chromosome biology in other diverse nematode species. We highlight malleable chromosome features including centromeres, telomeres, and repetitive elements, as well as the remarkable process of programmed DNA elimination (historically described as chromatin diminution) that induces loss of portions of the genome in somatic cells of a handful of nematode species. An exciting future prospect is that nematode species may enable experimental approaches to study chromosome features and to test models of chromosome evolution. In the long term, fundamental insights regarding how speciation is integrated with chromosome biology may be revealed.

The Elusive Mitochondrial Genomes of Apicomplexa: Where Are We Now?

Mitochondria are vital organelles of eukaryotic cells, participating in key metabolic pathways such as cellular respiration, thermogenesis, maintenance of cellular redox potential, calcium homeostasis, cell signaling, and cell death. The phylum Apicomplexa is entirely composed of obligate intracellular parasites, causing a plethora of severe diseases in humans, wild and domestic animals. These pathogens include the causative agents of malaria, cryptosporidiosis, neosporosis, East Coast fever and toxoplasmosis, among others. The mitochondria in Apicomplexa has been put forward as a promising source of undiscovered drug targets, and it has been validated as the target of atovaquone, a drug currently used in the clinic to counter malaria. Apicomplexans present a single tubular mitochondria that varies widely both in structure and in genomic content across the phylum. The organelle is characterized by massive gene migrations to the nucleus, sequence rearrangements and drastic functional reductions in some species. Recent third generation sequencing studies have reignited an interest for elucidating the extensive diversity displayed by the mitochondrial genomes of apicomplexans and their intriguing genomic features. The underlying mechanisms of gene transcription and translation are also ill-understood. In this review, we present the state of the art on mitochondrial genome structure, composition and organization in the apicomplexan phylum revisiting topological and biochemical information gathered through classical techniques. We contextualize this in light of the genomic insight gained by second and, more recently, third generation sequencing technologies. We discuss the mitochondrial genomic and mechanistic features found in evolutionarily related alveolates, and discuss the common and distinct origins of the apicomplexan mitochondria peculiarities.

The complete mitochondrial genome of Eimeria anseris from the wintering greater white-fronted goose in Shengjin Lake, China, and phylogenetic relationships among Eimeria species

Coccidiosis is recognized as one of the most widespread and pathogenic parasitic infections in migratory waterfowl throughout the world. It can be caused by several species of Eimeria. We sequenced the complete mitochondrial genome (mtDNA) of Eimeria anseris from wintering greater white-fronted geese (Anser albifrons) in China. The complete E. anseris mtDNA is 6179 bp in size and contains three protein-coding genes (CYT B, COI, and COIII), 12 gene fragments for large subunit ribosomal RNA (rRNA), and seven gene fragments for small subunit rRNA, but no transfer RNA genes. Available complete Eimeria mtDNA sequences are highly conserved in sequence: the sequences are all similar in length; with the same three protein-coding genes and fragmented rRNA genes; ATG is generally the start codon, and TAA and TAG are the most frequently used stop codons. Our molecular phylogenetic analyses show some species clustering into host-specific clades, but many species do not follow clear coevolutionary host segregating patterns. The results suggest that Eimeria spp. from turkeys and chickens are paraphyletic groups, while Eimeria species isolated from rabbits are a monophyletic group. E. anseris, which infects A. albifrons, and another group of Eimeria isolated from chickens form a closely related monophyletic clade.

Host species and pathogenicity effects in the evolution of the mitochondrial genomes of Eimeria species (Apicomplexa; Coccidia; Eimeriidae)

Background

Mitochondria are fundamental organelles responsible for cellular metabolism and energy production in eukaryotes via the oxidative phosphorylation pathway. Mitochondrial DNA is often used in population and species studies with the assumption of neutral evolution. However, evidence of positive selection in mitochondrial coding genes of various animal species has accumulated suggesting that amino acid changes in mtDNA might be adaptive. The functional and physiological implications of the inferred positively selected sites are usually unknown and are only evaluated based on available structural and functional models. Such studies are absent in unicellular organisms that show several crucial differences to the electron transport chain of animal mitochondria. In the present study, we explored Eimeria mitogenomes for positive selection. We also tested for association between mtDNA polymorphism and environmental variation (i.e. host species), parasite life cycle (i.e. sporulation period), and efficient host cell invasion (i.e. pathogenicity, prepatent period).

Findings

We used site- and branch-site tests to estimate the extent of purifying and positive selection at each site and each lineage of several Eimeria parasite mitogenomes retrieved from GenBank. We founded sixteen codons in the three mtDNA-encoded proteins to be under positive selection compared to a strong purifying selection. Variation in the ratios of non-synonymous to synonymous changes of the studied parasites was associated with their different host species (F = 13.748; p < 0.001), whereas pathogenicity levels were associated with both synonymous and non-synonymous changes. This association was also confirmed by the multiple regression analysis.

Conclusions

Our results suggest that host species and pathogenicity are important factors that might shape mitochondrial variation in Eimeria parasites. This supports the important role of mtDNA variations in the evolution and adaptation of these parasites.

Mitochondrial DNA Evidence Supports the Hypothesis that Triodontophorus Species Belong to Cyathostominae

Equine strongyles, the significant nematode pathogens of horses, are characterized by high quantities and species abundance, but classification of this group of parasitic nematodes is debated. Mitochondrial (mt) genome DNA data are often used to address classification controversies. Thus, the objectives of this study were to determine the complete mt genomes of three Cyathostominae nematode species (Cyathostomum catinatum, Cylicostephanus minutus, and Poteriostomum imparidentatum) of horses and reconstruct the phylogenetic relationship of Strongylidae with other nematodes in Strongyloidea to test the hypothesis that Triodontophorus spp. belong to Cyathostominae using the mt genomes. The mt genomes of Cy. catinatum, Cs. minutus, and P. imparidentatum were 13,838, 13,826, and 13,817 bp in length, respectively. Complete mt nucleotide sequence comparison of all Strongylidae nematodes revealed that sequence identity ranged from 77.8 to 91.6%. The mt genome sequences of Triodontophorus species had relatively high identity with Cyathostominae nematodes, rather than Strongylus species of the same subfamily (Strongylinae). Comparative analyses of mt genome organization for Strongyloidea nematodes sequenced to date revealed that members of this superfamily possess identical gene arrangements. Phylogenetic analyses using mtDNA data indicated that the Triodontophorus species clustered with Cyathostominae species instead of Strongylus species. The present study first determined the complete mt genome sequences of Cy. catinatum, Cs. minutus, and P. imparidentatum, which will provide novel genetic markers for further studies of Strongylidae taxonomy, population genetics, and systematics. Importantly, sequence comparison and phylogenetic analyses based on mtDNA sequences supported the hypothesis that Triodontophorus belongs to Cyathostominae.

The complete mitochondrial genome of Caryospora bigenetica (Eimeriidae, Eucoccidiorida, Coccidiasina, Apicomplexa)

The 6313 bp complete mitochondrial (mt) genome of Caryospora bigenetica was sequenced directly from PCR products. The mt genome was comparable in size, gene content and order to those of other Eimeriid coccidia (e.g. Isospora or Eimeria species). Three protein-coding genes encoding COI, COIII and CytB were identified; numerous rDNA fragments (19 LSU and 14 SSU) were interspersed among the CDS. Nucleotide composition was A + T biased (66%). The mitochondrial genomes of Eimeriid coccidia appear to share the same gene order and content; mt genome sequences can provide molecular data useful for diagnostics, taxonomy and phylogenetic relationships of Eimeriid coccidia.

Complete mitochondrial genome sequences from five Eimeria species (Apicomplexa; Coccidia; Eimeriidae) infecting domestic turkeys

BACKGROUND

Clinical and subclinical coccidiosis is cosmopolitan and inflicts significant losses to the poultry industry globally. Seven named Eimeria species are responsible for coccidiosis in turkeys: Eimeria dispersa; Eimeria meleagrimitis; Eimeria gallopavonis; Eimeria meleagridis; Eimeria adenoeides; Eimeria innocua; and, Eimeria subrotunda. Although attempts have been made to characterize these parasites molecularly at the nuclear 18S rDNA and ITS loci, the maternally-derived and mitotically replicating mitochondrial genome may be more suited for species level molecular work; however, only limited sequence data are available for Eimeria spp. infecting turkeys. The purpose of this study was to sequence and annotate the complete mitochondrial genomes from 5 Eimeria species that commonly infect the domestic turkey (Meleagris gallopavo).

METHODS

Six single-oocyst derived cultures of five Eimeria species infecting turkeys were PCR-amplified and sequenced completely prior to detailed annotation. Resulting sequences were aligned and used in phylogenetic analyses (BI, ML, and MP) that included complete mitochondrial genomes from 16 Eimeria species or concatenated CDS sequences from each genome.

RESULTS

Complete mitochondrial genome sequences were obtained for Eimeria adenoeides Guelph, 6211 bp; Eimeria dispersa Briston, 6238 bp; Eimeria meleagridis USAR97-01, 6212 bp; Eimeria meleagrimitis USMN08-01, 6165 bp; Eimeria gallopavonis Weybridge, 6215 bp; and Eimeria gallopavonis USKS06-01, 6215 bp). The order, orientation and CDS lengths of the three protein coding genes (COI, COIII and CytB) as well as rDNA fragments encoding ribosomal large and small subunit rRNA were conserved among all sequences. Pairwise sequence identities between species ranged from 88.1% to 98.2%; sequence variability was concentrated within CDS or between rDNA fragments (where indels were common). No phylogenetic reconstruction supported monophyly of Eimeria species infecting turkeys; Eimeria dispersa may have arisen via host switching from another avian host. Phylogenetic analyses suggest E. necatrix and E. tenella are related distantly to other Eimeria of chickens.

CONCLUSIONS

Mitochondrial genomes of Eimeria species sequenced to date are highly conserved with regard to gene content and structure. Nonetheless, complete mitochondrial genome sequences and, particularly the three CDS, possess sufficient sequence variability for differentiating Eimeria species of poultry. The mitochondrial genome sequences are highly suited for molecular diagnostics and phylogenetics of coccidia and, potentially, genetic markers for molecular epidemiology.