Search

Since its original launch in Lorne in 2000, the Molecular Approaches to Malaria Conference (MAM) has evolved as one of the most important conferences for malaria researchers globally. On February 23rd-27th this year, the sixth MAM took place in the same charming Australian coast town, bringing leading experts across diverse research fields to share the latest scientific advances and cutting-edge technologies in malaria research. Apart from the excellent science, the conference also set a standard for modern scientific events as a carbon neutral and gender balanced conference. In this TrendsTalk, we invite the section chairs to highlight the inspiring research across all section themes in the conference.

To monitor Symbiodiniaceae uptake and measure their colonization rate in Exaiptasia diaphana, we extended the methods presented in earlier works by including a calibration curve that allows symbiont coverage to be expressed as in hospite cell density. Our approach takes advantage of fluorescent microscopy and symbionts red chlorophyll auto-fluorescence.

To monitor Symbiodiniaceae uptake and measure their colonization rate in Exaiptasia pallida, we extended the methods presented in earlier works by including a calibration curve that allows symbiont coverage to be expressed as in hospite cell density. Our approach takes advantage of fluorescent microscopy and symbionts red chlorophyll auto-fluorescence.

We have synthesized new derivatives of the macrolide antibiotics erythromycin and azithromycin. Novel deoxysugar moieties were attached to these standard antibiotics by biotransformation using a heterologous host. The resulting compounds were tested against several standard laboratory and clinically isolated bacterial strains. In addition, they were also tested in vitro against standard and drug-resistant strains of human malaria parasites (Plasmodium falciparum) and the liver stages of the rodent malaria parasite (Plasmodium berghei). Antibacterial activity of modified erythromycin and azithromycin showed no improvement over the unmodified macrolides, but the modified compounds showed a 10-fold increase in effectiveness after a short-term exposure against blood stages of malaria. The new compounds also remained active against azithromycin-resistant strains of P. falciparum and inhibited growth of liver-stage parasites at concentrations similar to those used for primaquine. Our findings show that malaria parasites have two distinct responses to macrolide antibiotics, one reflecting the prokaryotic origin of the apicoplast and a second, as-yet uncharacterized response that we attribute to the eukaryotic nature of the parasite. This is the first report for macrolides that target two different functions in the Plasmodium parasites. Fil: Goodman, Christopher D.. The University of Melbourne; Australia Fil: Useglio, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina Fil: Peirú, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina Fil: Labadie, Guillermo Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: McFadden, Geoff. The University of Melbourne; Australia Fil: Rodriguez, Eduardo Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina Fil: Gramajo, Hugo Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina

Expression of a bacterial transporter protein in Toxoplasma gondii results in parasite susceptibility to Formidomycin, a drug targeting isoprenoid precursor synthesis., Apicomplexa are important pathogens that include the causative agents of malaria, toxoplasmosis, and cryptosporidiosis. Apicomplexan parasites contain a relict chloroplast, the apicoplast. The apicoplast is indispensable and an attractive drug target. The apicoplast is home to a 1-deoxy-d-xylulose-5-phosphate (DOXP) pathway for the synthesis of isoprenoid precursors. This pathway is believed to be the most conserved function of the apicoplast, and fosmidomycin, a specific inhibitor of the pathway, is an effective antimalarial. Surprisingly, fosmidomycin has no effect on most other apicomplexans. Using Toxoplasma gondii, we establish that the pathway is essential in parasites that are highly fosmidomycin resistant. We define the molecular basis of resistance and susceptibility, experimentally testing various host and parasite contributions in T. gondii and Plasmodium. We demonstrate that in T. gondii the parasite plasma membrane is a critical barrier to drug uptake. In strong support of this hypothesis, we engineer de novo drug-sensitive T. gondii parasites by heterologous expression of a bacterial transporter protein. Mice infected with these transgenic parasites can now be cured from a lethal challenge with fosmidomycin. We propose that the varied extent of metabolite exchange between host and parasite is a crucial determinator of drug susceptibility and a predictor of future resistance.

Microsporidia are obligate intracellular parasites that infect a wide range of eukaryotes, causing severe diseases in immunocompromised humans and losses to apiaries, fisheries and silk farms. They have often been considered to be primitive eukaryotes; however, more recent evidence suggests they are more closely related to fungi.

New molecular data confirm what electron microscopists long suspected - fusion of two different eukaryotic cells into a single more-complex cell created novel groups of protists. By engulfing an algal cell and putting it to work as a solar-powered food factory, heterotrophic protozoans became autotrophic. Drastically reduced, the engulfed cell now exists as an organelle in the host cell. Such blending of lineages was perhaps a driving force in early eukaryotic diversification.

The malaria parasite undergoes a remarkable series of morphological transformations, which underpin its life in both human and mosquito hosts. The advent of molecular transfection technology coupled with the ability to introduce fluorescent reporter proteins that faithfully track and expose the activities of parasite proteins has revolutionized our view of parasite cell biology. The greatest insights have been realized in the erythrocyte stages of Plasmodium falciparum. P. falciparum invades and remodels the human erythrocyte: it feeds on haemoglobin, grows and divides, and subverts the physiology of its hapless host. Fluorescent proteins have been employed to track and dissect each of these processes and have revealed details and exposed new paradigms.

Apical membrane antigen 1 of Plasmodium falciparum (PfAMA1) contains an N-terminal propeptide that is removed prior to the translocation of the mature protein onto the merozoite surface. We localized unprocessed PfAMA1 to the microneme organelles of the intraerythrocytic schizont. The results have suggested that the processed form of PfAMA1 translocates from the microneme compartment independently of another microneme protein, EBA175, which is also involved in the invasion of human erythrocytes.

Eubacterial and eukaryotic translation initiation systems have very little in common, and therefore the evolutionary events that gave rise to these two disparate systems are difficult to ascertain. One common feature is the presence of initiation, elongation, and release factors belonging to a large GTPase superfamily. One of these initiation factors, the gamma subunit of initiation factor 2 (eIF-2gamma), is found only in eukaryotes and archaebacteria. We have sequenced eIF-2gamma gene fragments from representative diplomonads, parabasalia, and microsporidia and used these new sequences together with new archaebacterial homologues to examine the phylogenetic position of eIF-2gamma within the GTPase superfamily. The archaebacterial and eukaryotic eIF-2gamma proteins are found to be very closely related, and are in turn related to SELB, the selenocysteine-specific elongation factor from eubacteria. The overall topology of the GTPase tree further suggests that the eIF-2gamma/SELB group may represent an ancient subfamily of GTPases that diverged prior to the last common ancestor of extant life.

Chlorarachniophytes are amoeboid algae with unusual chloroplasts. Instead of the usual two membranes that surround the chloroplasts of plants, green algae, and red algae, the chloroplasts of chlorarachniophytes have four bounding membranes. The extra membranes may reflect an unusual origin of chlorarachniophyte chloroplasts. Rather than inheriting the organelle directly from their ancestors, chlorarachniophytes may have adopted the chloroplast of an algal cell ingested as prey. Parts of the algal cell are postulated to remain within the amoeba as a reduced eukaryotic endosymbiont [Hibberd, D. J. & Norris, R. E. (1984) J. Phycol. 20, 310-330]. A small nucleus-like structure, proposed to be a vestige of the endosymbiont's nucleus, is located in a space between the second and third chloroplast membranes. We cloned and sequenced nuclear-type rRNA genes from chlorarachniophytes and found two highly divergent genes. In situ hybridization shows that one gene is expressed by the amoebal (host) nucleus and the other is expressed by the putative endosymbiont nucleus, suggesting that the latter is indeed a foreign genome. Transcripts from the endosymbiont gene accumulate in the small cytoplasmic compartment between the second and third chloroplast membranes, which we believe to be the remnant cytoplasm of the endosymbiont. Using the endosymbiont gene as a probe, we identified three small chromosomes belonging to the endosymbiont nucleus. This knowledge should allow a detailed molecular analysis of the role of the endosymbiont's genome and cytoplasm in the partnership.

The genome of the dinoflagellate chloroplast has been analysed, and it is decidedly odd. Chloroplasts are photosynthetic organelles, and in these marine algae their genome is composed of a small family of plasmid-like molecules each carrying a gene for a protein or ribosomal RNA. Tantalizing connections with the relict chloroplasts of the parasitesToxoplasma and Plasmodiumsuggest themselves.

The division Chlorarachniophyta comprises amoeboflagellate protists with complex chloroplasts derived from the endosymbiosis of a eukaryotic alga. Analysis of chlorarachniophyte chromosomal DNAs by pulsed-field gel electrophoresis revealed an apparently linear 36-kb chromosome that could not be ascribed to either the host or endosymbiont nuclei. A single eubacterial-like small subunit ribosomal RNA gene is encoded on this chromosome and phylogenetic analyses places this gene within a clade of mitochondrial genes from other eukaryotes. High resolution in situ hybridization demonstrates that transcripts of the small subunit ribosomal RNA gene encoded by the 36-kb chromosome are exclusively located in the mitochondria. The 36-kb chromosome thus likely represents a linear mitochondrial genome. Small amounts of an apparently dimeric (72 kb) form are also detectable in pulsed-field gel electrophoresis.

Dinoflagellates possess many cellular characteristics with unresolved evolutionary histories. These include nuclei with greatly expanded genomes and chromatin packaged using histone-like proteins and dinoflagellate-viral nucleoproteins instead of histones, highly reduced mitochondrial genomes with extensive RNA editing, a mix of photosynthetic and cryptic secondary plastids, and tertiary plastids. Resolving the evolutionary origin of these traits requires understanding their ancestral states and early intermediates. Several early-branching dinoflagellate lineages are good candidates for such reconstruction, however these cells tend to be delicate and environmentally sparse, complicating such analyses. Here, we employ transcriptome sequencing from manually isolated and microscopically documented cells to resolve the placement of two cells of one such genus, Abedinium, collected by remotely operated vehicle in deep waters off the coast of Monterey Bay, CA. One cell corresponds to the only described species, Abedinium dasypus, whereas the second cell is distinct and formally described as Abedinium folium, sp. nov. Abedinium has classically been assigned to the early-branching dinoflagellate subgroup Noctilucales, which is weakly supported by phylogenetic analyses of small subunit ribosomal RNA, the single characterized gene from any member of the order. However, an analysis based on 221 proteins from the transcriptome places Abedinium as a distinct lineage, separate from and basal to Noctilucales and the rest of the core dinoflagellates. The transcriptome also contains evidence of a cryptic plastid functioning in the biosynthesis of isoprenoids, iron-sulfur clusters, and heme, a mitochondrial genome with all three expected protein-coding genes (cob, cox1, and cox3), and the presence of some but not all dinoflagellate-specific chromatin packaging proteins.