Sequence and annotation of the apicoplast genome of the human pathogen Babesia microti

Apicoplast-Resident Processes: Exploiting the Chink in the Armour of Plasmodium falciparum Parasites

The discovery of a relict plastid, also known as an apicoplast (apicomplexan plastid), that houses housekeeping processes and metabolic pathways critical to Plasmodium parasites' survival has prompted increased research on identifying potent inhibitors that can impinge on apicoplast-localised processes. The apicoplast is absent in humans, yet it is proposed to originate from the eukaryote's secondary endosymbiosis of a primary symbiont. This symbiotic relationship provides a favourable microenvironment for metabolic processes such as haem biosynthesis, Fe-S cluster synthesis, isoprenoid biosynthesis, fatty acid synthesis, and housekeeping processes such as DNA replication, transcription, and translation, distinct from analogous mammalian processes. Recent advancements in comprehending the biology of the apicoplast reveal it as a vulnerable organelle for malaria parasites, offering numerous potential targets for effective antimalarial therapies. We provide an overview of the metabolic processes occurring in the apicoplast and discuss the organelle as a viable antimalarial target in light of current advances in drug discovery. We further highlighted the relevance of these metabolic processes to Plasmodium falciparum during the different stages of the lifecycle.

Effectiveness of Two New Endochin-like Quinolones, ELQ-596 and ELQ-650, in Experimental Mouse Models of Human Babesiosis

Endochin-like quinolones (ELQs) define a class of small molecule antimicrobials that target the mitochondrial electron transport chain of various human parasites by inhibiting their cytochrome bc1 complexes. The compounds have shown potent activity against a wide range of protozoan parasites, including the intraerythrocytic parasites Plasmodium and Babesia, the agents of human malaria and babesiosis, respectively. First-generation ELQ compounds were previously found to reduce infection by Babesia microti and Babesia duncani in animal models of human babesiosis but achieved a radical cure only in combination with atovaquone and required further optimization to address pharmacological limitations. Here, we report the identification of two second-generation 3-biaryl ELQ compounds, ELQ-596 and ELQ-650, with potent antibabesial activity in vitro and favorable pharmacological properties. In particular, ELQ-598, a prodrug of ELQ-596, demonstrated high efficacy as an orally administered monotherapy at 10 mg/kg. The compound achieved radical cure in both the chronic model of B. microti-induced babesiosis in immunocompromised mice and the lethal infection model induced by B. duncani in immunocompetent mice. Given its high potency, favorable physicochemical properties, and low toxicity profile, ELQ-596 represents a promising drug for the treatment of human babesiosis.

Transfusion-transmitted Babesia spp.: a changing landscape of epidemiology, regulation, and risk mitigation

Babesia spp. are tick-borne parasites with a global distribution and diversity of vertebrate hosts. Over the next several decades, climate change is expected to impact humans, vectors, and vertebrate hosts and change the epidemiology of Babesia. Although humans are dead-end hosts for tick-transmitted Babesia, human-to-human transmission of Babesia spp. from transfusion of red blood cells and whole blood-derived platelet concentrates has been reported. In most patients, transfusion-transmitted Babesia (TTB) results in a moderate-to-severe illness. Currently, in North America, most cases of TTB have been described in the United States. TTB cases outside North America are rare, but case numbers may change over time with increased recognition of babesiosis and as the epidemiology of Babesia is impacted by climate change. Therefore, TTB is a concern of microbiologists working in blood operator settings, as well as in clinical settings where transfusion occurs. Microbiologists play an important role in deploying blood donor screening assays in Babesia endemic regions, identifying changing risks for Babesia in non-endemic areas, investigating recipients of blood products for TTB, and drafting TTB policies and guidelines. In this review, we provide an overview of the clinical presentation and epidemiology of TTB. We identify approaches and technologies to reduce the risk of collecting blood products from Babesia-infected donors and describe how investigations of TTB are undertaken. We also describe how microbiologists in Babesia non-endemic regions can assess for changing risks of TTB and decide when to focus on laboratory-test-based approaches or pathogen reduction to reduce TTB risk.

Babesia gibsoni Whole-Genome Sequencing, Assembling, Annotation, and Comparative Analysis

The intracellular protozoan parasite Babesia gibsoni infects canine erythrocytes and causes babesiosis. The hazards to animal health have increased due to the rise of B. gibsoni infections and medication resistance. However, the lack of high-quality full-genome sequencing sets has expanded the obstacles to the development of pathogeneses, drugs, and vaccines. In this study, the whole genome of B. gibsoni was sequenced, assembled, and annotated. The genomic size of B. gibsoni was 7.94 Mbp in total. Four chromosomes with the size of 0.69 Mb, 2.10 Mb, 2.77 Mb, and 2.38 Mb, respectively, 1 apicoplast (28.4 Kb), and 1 mitochondrion (5.9 Kb) were confirmed. KEGG analysis revealed 2,641 putative proteins enriched on 316 pathways, and GO analysis showed 7,571 annotations of the nuclear genome in total. Synteny analysis showed a high correlation between B. gibsoni and B. bovis. A new divergent point of B. gibsoni occurred around 297.7 million years ago, which was earlier than that of B. bovis, B. ovata, and B. bigemina. Orthology analysis revealed 22 and 32 unique genes compared to several Babesia spp. and apicomplexan species. The metabolic pathways of B.gibsoni were characterized, pointing to a minimal size of the genome. A species-specific secretory protein SA1 and 19 homologous genes were identified. Selected specific proteins, including apetala 2 (AP2) factor, invasion-related proteins BgAMA-1 and BgRON2, and rhoptry function proteins BgWH_04g00700 were predicted, visualized, and modeled. Overall, whole-genome sequencing provided molecular-level support for the diagnosis, prevention, clinical treatment, and further research of B. gibsoni. IMPORTANCE The whole genome of B. gibsoni was first sequenced, annotated, and disclosed. The key part of genome composition, four chromosomes, was comparatively analyzed for the first time. A full-scale phylogeny evolution analysis based on the whole-genome-wide data of B. gibsoni was performed, and a new divergent point on the evolutionary path was revealed. In previous reports, molecular studies were often limited by incomplete genomic data, especially in key areas like life cycle regulation, metabolism, and host-pathogen interaction. With the whole-genome sequencing of B. gibsoni, we provide useful genetic data to encourage the exploration of new terrain and make it feasible to resolve the theoretical and practical problems of babesiosis.

New insights into apicoplast metabolism in blood-stage malaria parasites

The apicoplast of Plasmodium falciparum is the only source of essential isoprenoid precursors and Coenzyme A (CoA) in the parasite. Isoprenoid precursor synthesis relies on the iron-sulfur cluster (FeS) cofactors produced within the apicoplast, rendering FeS synthesis an essential function of this organelle. Recent reports provide important insights into the roles of FeS cofactors and the use of isoprenoid precursors and CoA both inside and outside the apicoplast. Here, we review the recent insights into the roles of these metabolites in blood-stage malaria parasites and discuss new questions that have been raised in light of these discoveries.

Plasmodium-a brief introduction to the parasites causing human malaria and their basic biology

Malaria is one of the most devastating infectious diseases of humans. It is problematic clinically and economically as it prevails in poorer countries and regions, strongly hindering socioeconomic development. The causative agents of malaria are unicellular protozoan parasites belonging to the genus Plasmodium. These parasites infect not only humans but also other vertebrates, from reptiles and birds to mammals. To date, over 200 species of Plasmodium have been formally described, and each species infects a certain range of hosts. Plasmodium species that naturally infect humans and cause malaria in large areas of the world are limited to five—P. falciparum, P. vivax, P. malariae, P. ovale and P. knowlesi. The first four are specific for humans, while P. knowlesi is naturally maintained in macaque monkeys and causes zoonotic malaria widely in South East Asia. Transmission of Plasmodium species between vertebrate hosts depends on an insect vector, which is usually the mosquito. The vector is not just a carrier but the definitive host, where sexual reproduction of Plasmodium species occurs, and the parasite’s development in the insect is essential for transmission to the next vertebrate host. The range of insect species that can support the critical development of Plasmodium depends on the individual parasite species, but all five Plasmodium species causing malaria in humans are transmitted exclusively by anopheline mosquitoes. Plasmodium species have remarkable genetic flexibility which lets them adapt to alterations in the environment, giving them the potential to quickly develop resistance to therapeutics such as antimalarials and to change host specificity. In this article, selected topics involving the Plasmodium species that cause malaria in humans are reviewed.

Annotation and characterization of Babesia gibsoni apicoplast genome

Background

Babesia gibsoni is an apicomplexan parasite transmitted by ticks, which can infect canine species and cause babesiosis. The apicoplast is an organelle associated with isoprenoids metabolism, is widely present in apicomplexan parasites, except for Cryptosporidium. Available data indicate that the apicoplast is essential for the survival of apicomplexan parasites.

Methods

Here, the apicoplast genome of B. gibsoni was investigated by high-throughput genome sequencing, bioinformatics analysis, and conventional PCR.

Results

The apicoplast genome of B. gibsoni-Wuhan strain (B. gibsoni-WH) consists of a 28.4 kb circular molecule, with A + T content of 86.33%, similar to that of B. microti. Specifically, this genome encodes genes involved in maintenance of the apicoplast DNA, transcription, translation and maturation of organellar proteins, which contains 2 subunits of ribosomal RNAs, 17 ribosomal proteins, 1 EF-Tu elongation factor (tufA), 5 DNA-dependent RNA polymerase beta subunits, 2 Clp protease chaperones, 23 tRNA genes and 5 unknown open reading frames (hypothetical proteins). Phylogenetic analysis revealed high similarity of B. gibsoni apicoplast genome to that of B. orientalis and B. bovis.

Conclusions

To our knowledge, this is the first report of annotation and characterization of B. gibsoni-WH apicoplast genome. The results will facilitate the development of new anti-Babesia drug targets.

There Is Treasure Everywhere: Reductive Plastid Evolution in Apicomplexa in Light of Their Close Relatives

The phylum Apicomplexa (Alveolates) comprises a group of host-associated protists, predominately intracellular parasites, including devastating parasites like Plasmodium falciparum, the causative agent of malaria. One of the more fascinating characteristics of Apicomplexa is their highly reduced (and occasionally lost) remnant plastid, termed the apicoplast. Four core metabolic pathways are retained in the apicoplast: heme synthesis, iron–sulfur cluster synthesis, isoprenoid synthesis, and fatty acid synthesis. It has been suggested that one or more of these pathways are essential for plastid and plastid genome retention. The past decade has witnessed the discovery of several apicomplexan relatives, and next-generation sequencing efforts are revealing that they retain variable plastid metabolic capacities. These data are providing clues about the core genes and pathways of reduced plastids, while at the same time further confounding our view on the evolutionary history of the apicoplast. Here, we examine the evolutionary history of the apicoplast, explore plastid metabolism in Apicomplexa and their close relatives, and propose that the differences among reduced plastids result from a game of endosymbiotic roulette. Continued exploration of the Apicomplexa and their relatives is sure to provide new insights into the evolution of the apicoplast and apicomplexans as a whole.

Clinical and Molecular Evidence of Atovaquone and Azithromycin Resistance in Relapsed Babesia microti Infection Associated With Rituximab and Chronic Lymphocytic Leukemia

Babesiosis treatment failures with standard therapy have been reported, but the molecular mechanisms are not well understood. We describe the emergence of atovaquone and azithromycin resistance associated with mutations in the binding regions of the target proteins of both drugs during treatment of an immunosuppressed patient with relapsing babesiosis.

Comparative analysis of apicoplast genomes of Babesia infective to small ruminants in China

Background

Babesiosis is an economically important disease caused by tick-borne apicomplexan protists of the genus Babesia. Most apicomplexan parasites, including Babesia, have a plastid-derived organelle termed an apicoplast, which is involved in critical metabolic pathways such as fatty acid, iron-sulphur, haem and isoprenoid biosynthesis. Apicoplast genomic data can provide significant information for understanding and exploring the biological features, taxonomic and evolutionary relationships of apicomplexan parasites, and identify targets for anti-parasitic drugs. However, there are limited data on the apicoplast genomes of Babesia species infective to small ruminants.

Methods

PCR primers were designed based on the previously reported apicoplast genome sequences of Babesia motasi Lintan and Babesia sp. Xinjiang using Illumina technology. The overlapped apicoplast genomic fragments of six ovine Babesia isolates were amplified and sequenced using the Sanger dideoxy chain-termination method. The full-length sequences of the apicoplast genomes were assembled and annotated using bioinformatics software. The gene contents and order of apicoplast genomes obtained in this study were defined and compared with those of other apicomplexan parasites. Phylogenetic trees were constructed on the concatenated amino acid sequences of 13 gene products using MEGA v.6.06.

Results

The results showed that the six ovine Babesia apicoplast genomes consisted of circular DNA. The genome sizes were 29,916–30,846 bp with 78.7–81.0% A + T content, 29–31 open reading frames (ORF) and 23–24 transport RNAs. The ORFs encoded four DNA-directed RNA polymerase subunits (rpoB, rpoCl, rpoC2a and rpoC2b), 13 ribosomal proteins, one elongation factor TU (tufA), two ATP-dependent Clp proteases (ClpC) and 7–11 hypothetical proteins. Babesia sp. has three more genes than Babesia motasi (rpl5, rps8 and rpoB). Phylogenetic analysis showed that Babesia sp. is located in a separate clade. Babesia motasi Lintan/Tianzhu and B. motasi Ningxian/Hebei were divided into two subclades.

Conclusions

To our knowledge, this study is the first to elucidate the whole apicoplast genomic structural features of six Babesia isolates infective to small ruminants in China using Sanger sequencing. The data provide useful information confirming the taxonomic relationships of these parasites and identifying targets for anti-apicomplexan parasite drugs.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3581-x) contains supplementary material, which is available to authorized users.

Evidence for vesicle-mediated antigen export by the human pathogen Babesia microti

The human pathogen Babesia microti undergoes unique morphogenesis during its development within human and mouse red blood cells and uses a novel vesicle-based system for export of antigens into the host cell and environment.

The apicomplexan parasite Babesia microti is the primary agent of human babesiosis, a malaria-like illness and potentially fatal tick-borne disease. Unlike its close relatives, the agents of human malaria, B. microti develops within human and mouse red blood cells in the absence of a parasitophorous vacuole, and its secreted antigens lack trafficking motifs found in malarial secreted antigens. Here, we show that after invasion of erythrocytes, B. microti undergoes a major morphogenic change during which it produces an interlacement of vesicles (IOV); the IOV system extends from the plasma membrane of the parasite into the cytoplasm of the host erythrocyte. We developed antibodies against two immunodominant antigens of the parasite and used them in cell fractionation studies and fluorescence and immunoelectron microscopy analyses to monitor the mode of secretion of B. microti antigens. These analyses demonstrate that the IOV system serves as a major export mechanism for important antigens of B. microti and represents a novel mechanism for delivery of parasite effectors into the host by this apicomplexan parasite.

Insights into the evolution and drug susceptibility of Babesia duncani from the sequence of its mitochondrial and apicoplast genomes

Babesia microti and Babesia duncani are the main causative agents of human babesiosis in the United States. While significant knowledge about B. microti has been gained over the past few years, nothing is known about B. duncani biology, pathogenesis, mode of transmission or sensitivity to currently recommended therapies. Studies in immunocompetent wild type mice and hamsters have shown that unlike B. microti, infection with B. duncani results in severe pathology and ultimately death. The parasite factors involved in B. duncani virulence remain unknown. Here we report the first known completed sequence and annotation of the apicoplast and mitochondrial genomes of B. duncani. We found that the apicoplast genome of this parasite consists of a 34 kb monocistronic circular molecule encoding functions that are important for apicoplast gene transcription as well as translation and maturation of the organelle's proteins. The mitochondrial genome of B. duncani consists of a 5.9 kb monocistronic linear molecule with two inverted repeats of 48 bp at both ends. Using the conserved cytochrome b (Cytb) and cytochrome c oxidase subunit I (coxI) proteins encoded by the mitochondrial genome, phylogenetic analysis revealed that B. duncani defines a new lineage among apicomplexan parasites distinct from B. microti, Babesia bovis, Theileria spp. and Plasmodium spp. Annotation of the apicoplast and mitochondrial genomes of B. duncani identified targets for development of effective therapies. Our studies set the stage for evaluation of the efficacy of these drugs alone or in combination against B. duncani in culture as well as in animal models.

Case report of the patient source of the Babesia microti R1 reference strain and implications for travelers

BACKGROUND

In 2002, a previously healthy 69-year-old man travelled to France from the United States and presented to our hospital with a febrile illness that subsequently was determined to be babesiosis. The blood isolated from this patient served as a source for propagation of the Babesia microti R1 strain with subsequent sequencing and annotation of the parasite genome.

METHODS

Upon admission, we obtained a medical history, performed a physical examination, and examined his blood for the presence of a blood borne pathogen by microscopy, PCR and indirect immunofluorescence antibody testing. Once the diagnosis of babesiosis was made, we reviewed the literature to assess the distribution of B. microti-associated babesiosis cases in immunocompetent patients from outside the USA.

RESULTS

The patient recalled a tick bite during the previous month on Cape Cod, Massachusetts. The diagnosis was confirmed by identification of Babesia-infected red blood cells on blood smears, amplification of B. microti DNA in blood by PCR and the presence of B. microti antibody in the serum. This strain was the first isolate of B. microti to be fully sequenced and its annotated genome serves as a reference for molecular and cell biology studies aimed at understanding B. microti pathophysiology and developing diagnostic tests and therapies. A review of babesiosis cases demonstrates a worldwide distribution of B. microti and identifies potential emerging endemic areas where travelers may be at risk of contracting B. microti infection.

CONCLUSION

This case provides clinical information about the patient infected with the R1 isolate and a review of travel risk, diagnosis and treatment of babesiosis in endemic and non-endemic areas.

Comparative sequence analysis of Cyclospora cayetanensis apicoplast genomes originating from diverse geographical regions

BACKGROUND

Cyclospora cayetanensis is an emerging coccidian parasite that causes endemic and epidemic diarrheal disease called cyclosporiasis, and this infection is associated with consumption of contaminated produce or water in developed and developing regions. Food-borne outbreaks of cyclosporiasis have occurred almost every year in the USA since the 1990s. Investigations of these outbreaks are currently hampered due to lack of molecular epidemiological tools for trace back analysis. The apicoplast of C. cayetanensis, a relict non-photosynthetic plastid with an independent genome, provides an attractive target to discover sequence polymorphisms useful as genetic markers for detection and trace back analysis of the parasite. Distinct differences in the apicoplast genomes of C. cayetanensis could be useful in designing advanced molecular methods for rapid detection and, subtyping and geographical source attribution, which would aid outbreak investigations and surveillance studies.

METHODS

To obtain the genome sequence of the C. cayetanensis apicoplast, we sequenced the C. cayetanensis genomic DNA extracted from clinical stool samples, assembled and annotated a 34,146 bp-long circular sequence, and used this sequence as a reference genome in this study. We compared the genome and the predicted proteome to the data available from other apicomplexan parasites. To initialize the search for genetic markers, we mapped the raw sequence reads from an additional 11 distinct clinical stool samples originating from Nepal, New York, Texas, and Indonesia to the apicoplast reference genome.

RESULTS

We identified several high quality single nucleotide polymorphisms (SNPs) and small insertion/deletions spanning the apicoplast genome supported by extensive sequencing reads data, and a 30 bp sequence repeat at the terminal spacer region in a Nepalese sample. The predicted proteome consists of 29 core apicomplexan peptides found in most of the apicomplexans. Cluster analysis of these C. cayetanensis apicoplast genomes revealed a familiar pattern of tight grouping with Eimeria and Toxoplasma, separated from distant species such as Plasmodium and Babesia.

CONCLUSIONS

SNPs and sequence repeats identified in this study may be useful as genetic markers for identification and differentiation of C. cayetanensis isolates found and could facilitate outbreak investigations.

Babesia microti from humans and ticks hold a genomic signature of strong population structure in the United States

Background

Babesia microti is an emerging tick-borne apicomplexan parasite with increasing geographic range and incidence in the United States. The rapid expansion of B. microti into its current distribution in the northeastern USA has been due to the range expansion of the tick vector, Ixodes scapularis, upon which the causative agent is dependent for transmission to humans.

Results

To reconstruct the history of B. microti in the continental USA and clarify the evolutionary origin of human strains, we used multiplexed hybrid capture of 25 B. microti isolates obtained from I. scapularis and human blood. Despite low genomic variation compared with other Apicomplexa, B. microti was strongly structured into three highly differentiated genetic clusters in the northeastern USA. Bayesian analyses of the apicoplast genomes suggest that the origin of the current diversity of B. microti in northeastern USA dates back 46 thousand years with a signature of recent population expansion in the last 1000 years. Human-derived samples belonged to two rarely intermixing clusters, raising the possibility of highly divergent infectious phenotypes in humans.

Conclusions

Our results validate the multiplexed hybrid capture strategy for characterizing genome-wide diversity and relatedness of B. microti from ticks and humans. We find strong population structure in B. microti samples from the Northeast indicating potential barriers to gene flow.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3225-x) contains supplementary material, which is available to authorized users.

The apicoplast genomes of two taxonomic units of Babesia from sheep

The apicoplast (ap) is a unique, non-photosynthetic organelle found in most apicomplexan parasites. Due to the essential roles that this organelle has, it has been widely considered as target for drugs against diseases caused by apicomplexans. Exploring the ap genomes of such parasites would provide a better understanding of their systematics and their basic molecular biology for therapeutics. However, there is limited information available on the ap genomes of apicomplexan parasites. In the present study, the ap genomes of two operational taxonomic units of Babesia (known as Babesia sp. Lintan [Bl] and Babesia sp. Xinjiang [Bx]) from sheep were sequenced, assembled and annotated using a massive parallel sequencing-based approach. Then, the gene content and gene order in these ap genomes (∼30.7kb in size) were defined and compared, and the genetic differences were assessed. In addition, a phylogenetic analysis of ap genomic data sets was carried out to assess the relationships of these taxonomic units with other apicomplexan parasites for which complete ap genomic data sets were publicly available. The results showed that the ap genomes of Bl and Bx encode 59 and 57 genes, respectively, including 2 ribosomal RNA genes, 25 transfer RNA genes and 30-32 protein-encoding genes, being similar in content to those of Babesia bovis and B. orientalis. Ap gene regions that might serve as markers for future epidemiological and population genetic studies of Babesia species were identified. Using sequence data for a subset of six protein-encoding genes, a close relationship of Bl and Bx with Babesia bovis from cattle and B. orientalis from water buffalo was inferred. Although the focus of the present study was on Babesia, we propose that the present sequencing-bioinformatic approach should be applicable to organellar genomes of a wide range of apicomplexans of veterinary importance.

A method for identification of highly conserved elements and evolutionary analysis of superphylum Alveolata

Background

Perfectly or highly conserved DNA elements were found in vertebrates, invertebrates, and plants by various methods. However, little is known about such elements in protists. The evolutionary distance between apicomplexans can be very high, in particular, due to the positive selection pressure on them. This complicates the identification of highly conserved elements in alveolates, which is overcome by the proposed algorithm.

Results

A novel algorithm is developed to identify highly conserved DNA elements. It is based on the identification of dense subgraphs in a specially built multipartite graph (whose parts correspond to genomes). Specifically, the algorithm does not rely on genome alignments, nor pre-identified perfectly conserved elements; instead, it performs a fast search for pairs of words (in different genomes) of maximum length with the difference below the specified edit distance. Such pair defines an edge whose weight equals the maximum (or total) length of words assigned to its ends. The graph composed of these edges is then compacted by merging some of its edges and vertices. The dense subgraphs are identified by a cellular automaton-like algorithm; each subgraph defines a cluster composed of similar inextensible words from different genomes. Almost all clusters are considered as predicted highly conserved elements. The algorithm is applied to the nuclear genomes of the superphylum Alveolata, and the corresponding phylogenetic tree is built and discussed.

Conclusion

We proposed an algorithm for the identification of highly conserved elements. The multitude of identified elements was used to infer the phylogeny of Alveolata.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-016-1257-5) contains supplementary material, which is available to authorized users.

Regulation of Expression and Evolution of Genes in Plastids of Rhodophytic Branch

A novel algorithm and original software were used to cluster all proteins encoded in plastids of 72 species of the rhodophytic branch. The results are publicly available at http://lab6.iitp.ru/ppc/redline72/ in a database that allows fast identification of clusters (protein families) both by a fragment of an amino acid sequence and by a phylogenetic profile of a protein. No such integral clustering with the corresponding functions can be found in the public domain. The putative regulons of the transcription factors Ycf28 and Ycf29 encoded in the plastids were identified using the clustering and the database. A regulation of translation initiation was proposed for the ycf24 gene in plastids of certain red algae and apicomplexans as well as a regulation of a putative gene in apicoplasts of Babesia spp. and Theileria parva. The conserved regulation of the ycf24 gene expression and specificity alternation of the transcription factor Ycf28 were shown in the plastids. A phylogenetic tree of plastids was generated for the rhodophytic branch. The hypothesis of the origin of apicoplasts from the common ancestor of all apicomplexans from plastids of red algae was confirmed.

Algorithms for reconstruction of chromosomal structures

BACKGROUND

One of the main aims of phylogenomics is the reconstruction of objects defined in the leaves along the whole phylogenetic tree to minimize the specified functional, which may also include the phylogenetic tree generation. Such objects can include nucleotide and amino acid sequences, chromosomal structures, etc. The structures can have any set of linear and circular chromosomes, variable gene composition and include any number of paralogs, as well as any weights of individual evolutionary operations to transform a chromosome structure. Many heuristic algorithms were proposed for this purpose, but there are just a few exact algorithms with low (linear, cubic or similar) polynomial computational complexity among them to our knowledge. The algorithms naturally start from the calculation of both the distance between two structures and the shortest sequence of operations transforming one structure into another. Such calculation per se is an NP-hard problem.

RESULTS

A general model of chromosomal structure rearrangements is considered. Exact algorithms with almost linear or cubic polynomial complexities have been developed to solve the problems for the case of any chromosomal structure but with certain limitations on operation weights. The computer programs are tested on biological data for the problem of mitochondrial or plastid chromosomal structure reconstruction. To our knowledge, no computer programs are available for this model.

CONCLUSIONS

Exactness of the proposed algorithms and such low polynomial complexities were proved. The reconstructed evolutionary trees of mitochondrial and plastid chromosomal structures as well as the ancestral states of the structures appear to be reasonable.