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Author: Donna Huber

Metabolic dependency of chorismate in Plasmodium falciparum suggests an alternative source for the ubiquinone biosynthesis precursor

The shikimate pathway, a metabolic pathway absent in humans, is responsible for the production of chorismate, a branch point metabolite. In the malaria parasite, chorismate is postulated to be a direct precursor in the synthesis of p-aminobenzoic acid (folate biosynthesis), p-hydroxybenzoic acid (ubiquinone biosynthesis), menaquinone, and aromatic amino acids. While the potential value of the shikimate pathway as a drug target is debatable, the metabolic dependency of chorismate in P. falciparum remains unclear. Current evidence suggests that the main role of chorismate is folate biosynthesis despite ubiquinone biosynthesis being active and essential in the malaria parasite. Our goal in the present work was to expand our knowledge of the ubiquinone head group biosynthesis and its potential metabolic dependency on chorismate in P. falciparum. We systematically assessed the development of both asexual and sexual stages of P. falciparum in a defined medium in the absence of an exogenous supply of chorismate end-products and present biochemical evidence suggesting that the benzoquinone ring of ubiquinones in this parasite may be synthesized through a yet unidentified route.

Ana Lisa Valenciano, Maria L. Fernández-Murga, Emilio F. Merino, Nicole R. Holderman, Grant J. Butschek, Karl J. Shaffer, Peter C. Tyler & Maria Belen Cassera. 2019. Sci Rep.;9(1):13936. doi: 10.1038/s41598-019-50319-5.

Clinically silent relapsing malaria may still pose a threat

The immune system can control a relapsing form of malaria enough to avoid clinical signs of disease, but it doesn’t eliminate transmissible parasites from the body that may still be infectious to mosquitoes. That’s the conclusion of a study on a nonhuman primate model of Plasmodium vivax infection, which has implications relevant to malaria elimination strategies.

Keep reading about the MaPHIC study at

Humoral immunity prevents clinical malaria during Plasmodium relapses without eliminating gametocytes

Plasmodium relapses are attributed to the activation of dormant liver-stage parasites and are responsible for a significant number of recurring malaria blood-stage infections. While characteristic of human infections caused by Pvivax and Povale, their relative contribution to malaria disease burden and transmission remains poorly understood. This is largely because it is difficult to identify ‘bona fide’ relapse infections due to ongoing transmission in most endemic areas. Here, we use the Pcynomolgi–rhesus macaque model of relapsing malaria to demonstrate that clinical immunity can form after a single sporozoite-initiated blood-stage infection and prevent illness during relapses and homologous reinfections. By integrating data from whole blood RNA-sequencing, flow cytometry, Pcynomolgi-specific ELISAs, and opsonic phagocytosis assays, we demonstrate that this immunity is associated with a rapid recall response by memory B cells that expand and produce anti-parasite IgG1 that can mediate parasite clearance of relapsing parasites. The reduction in parasitemia during relapses was mirrored by a reduction in the total number of circulating gametocytes, but importantly, the cumulative proportion of gametocytes increased during relapses. Overall, this study reveals that Pcynomolgi relapse infections can be clinically silent in macaques due to rapid memory B cell responses that help to clear asexual-stage parasites but still carry gametocytes.

Joyner CJ, Brito CFA, Saney CL, Joice Cordy R, Smith ML, Lapp SA, Cabrera-Mora M, Kyu S, Lackman N, Nural MV, DeBarry JD, MaHPIC Consortium, Kissinger JC, Styczynski MP, Lee FE, Lamb TJ, Galinski MR.. (2019) Humoral immunity prevents clinical malaria during Plasmodium relapses without eliminating gametocytes. PLoS Pathog 15(9): e1007974.

Is reliance on an inaccurate genome sequence sabotaging your experiments?

Advances in genomics have made whole genome studies increasingly feasible across the life sciences. However, new technologies and algorithmic advances do not guarantee flawless genomic sequences or annotation. Bias, errors, and artifacts can enter at any stage of the process from library preparation to annotation. When planning an experiment that utilizes a genome sequence as the basis for the design, there are a few basic checks that, if performed, may better inform the experimental design and ideally help avoid a failed experiment or inconclusive result.

Baptista RP, Kissinger JC (2019) Is reliance on an inaccurate genome sequence sabotaging your experiments? PLoS Pathog 15(9): e1007901.

Visiting Scholar Fellow: Fernando Sanchez-Valdéz

Fellow: Fernando Sanchez ValdezDr. Fernando Sanchez-Valdéz, from Salta, Argentina, completed a Ph.D. in Molecular Biology at the Faculty of Pharmacy and Biochemistry at the University of Buenos Aires, Argentina in 2014. After his Ph.D., he completed a postdoctoral fellowship in Dr. Rick Tarleton´s laboratory at University of Georgia. In 2018, he obtained a Research Scientist position in the career pathway of the National Research Council in Argentina (CONICET). Earlier this year, he was awarded a fellowship from the CTEGD-Janssen Visiting Scholars Program, which enabled him to return to the Tarleton Research Group.

What is your primary research focus? Why are you interested in this subject?

The main focus of my research has been to uncover the mechanism of drug resistance in the Chagas disease agent, Trypanosoma cruzi. The main question we are trying to answer is why the treatment with highly effective drugs like Benznidazole (the current available treatment for Chagas disease) often fails to cure Chagas disease. By combining ex vivo luminescence assays and tissue-clearing techniques we were able to report, for the first time, the presence of dormant non-replicating amastigotes forms in the chronic phase of the disease. Dormant amastigotes were uniquely resistant to extended drug treatment in vivo and in vitro and could re-establish a flourishing infection after treatment interruption. T. cruzi‘s capacity to become dormant makes them transiently drug-resistant, suggesting that this phenomenon accounts for the failure of the otherwise highly active compounds such Benznidazole (Sanchez-Valdéz, et al eLife 2018).

Why did you choose UGA?

I returned to Athens in February 2019 to continue working on the findings we made during my postdoctoral training in the Tarleton Laboratory. I initially decided to come UGA based on a colleague’s recommendations and the fact that Tarleton´s lab is one of the reference centers for Chagas disease research. It’s a really motivating environment to do science since the scientific and technical level here is really high as well as diverse including areas as immunology, drug discovery, genetic manipulation, genomics, diagnostics, etc. Also the amount of resources available is impressive not only from the lab but also from the Biomedical Microscopy Core, Cytometry Shared Resource Laboratory and the animal facility at UGA.

What has been your research project while at UGA?

Currently, we are expanding our knowledge about T. cruzi dormancy and trying to interfere T. cruzi dormancy using new compounds or the conventional drugs but in a different treatment schedule. One of the approaches we are testing now involves the evaluation of drug doses and treatment schemes able to kill dormant parasites. For this purpose, we are optimizing a robust platform to detect low levels of parasites in whole clarified mice organs using light-sheet fluorescent microscopy. This technique will allow us the specific detection of low levels of persistent dormant parasites.

How has the CTEGD-Janssen Visiting Scholar Fellowship and your time at UGA impacted your research and professional goals?

I am so glad about the opportunity to continue working on T. cruzi dormancy with such experienced and renowned scientists and particularly using state-of-the-art microscopy techniques currently unavailable in South America. This experience will definitely have a positive impact on my career development and probably in the Chagas disease research field.

Accessing Cryptosporidium Omic and Isolate Data via

Cryptosporidium has historically been a difficult organism to work with, and molecular genomic data for this important pathogen have typically lagged behind other prominent protist pathogens. CryptoDB ( ) was launched in 2004 following the appearance of draft genome sequences for both C. parvum and C. hominis. CryptoDB merged with the EuPathDB Bioinformatics Resource Center family of databases ( ) and has been maintained and updated regularly since its establishment. These resources are freely available, are web-based, and permit users to analyze their own sequence data in the context of reference genome sequences in our user workspaces. Advances in technology have greatly facilitated Cryptosporidium research in the last several years greatly enhancing and extending the data and types of data available for this genus. Currently, 13 genome sequences are available for 9 species of Cryptosporidium as well as the distantly related Gregarina niphandrodes and two free-living alveolate outgroups of the Apicomplexa, Chromera velia and Vitrella brassicaformis. Recent years have seen several new genome sequences for both existing and new Cryptosporidium species as well as transcriptomics, proteomics, SNP, and isolate population surveys. This chapter introduces the extensive data mining and visualization capabilities of the EuPathDB software platform and introduces the data types and tools that are currently available for Cryptosporidium. Key features are demonstrated with Cryptosporidium-relevant examples and explanations.

Warrenfeltz S, Kissinger JC, EuPathDB Team. Methods Mol Biol. 2020;2052:139-192. doi: 10.1007/978-1-4939-9748-0_10.

Protozoan persister-like cells and drug treatment failure

Antimicrobial treatment failure threatens our ability to control infections. In addition to antimicrobial resistance, treatment failures are increasingly understood to derive from cells that survive drug treatment without selection of genetically heritable mutations. Parasitic protozoa, such as Plasmodium species that cause malaria, Toxoplasma gondii and kinetoplastid protozoa, including Trypanosoma cruzi and Leishmaniaspp., cause millions of deaths globally. These organisms can evolve drug resistance and they also exhibit phenotypic diversity, including the formation of quiescent or dormant forms that contribute to the establishment of long-term infections that are refractory to drug treatment, which we refer to as ‘persister-like cells’. In this Review, we discuss protozoan persister-like cells that have been linked to persistent infections and discuss their impact on therapeutic outcomes following drug treatment.

Michael P. Barrett, Dennis E. Kyle, L. David Sibley, Joshua B. Radke & Rick L. Tarleton. Nat Rev Microbiol. 2019 Aug 23. doi: 10.1038/s41579-019-0238-x.

Enteropathogen antibody dynamics and force of infection among children in low-resource settings

Little is known about enteropathogen seroepidemiology among children in low-resource settings. We measured serological IgG responses to eight enteropathogens (Giardia intestinalis, Cryptosporidium parvum, Entamoeba histolytica, Salmonella enterica, enterotoxigenic Escherichia coliVibrio cholerae, Campylobacter jejuni, norovirus) in cohorts from Haiti, Kenya, and Tanzania. We studied antibody dynamics and force of infection across pathogens and cohorts. Enteropathogens shared common seroepidemiologic features that enabled between-pathogen comparisons of transmission. Overall, exposure was intense: for most pathogens the window of primary infection was <3 years old; for highest transmission pathogens primary infection occurred within the first year. Longitudinal profiles demonstrated significant IgG boosting and waning above seropositivity cutoffs, underscoring the value of longitudinal designs to estimate force of infection. Seroprevalence and force of infection were rank-preserving across pathogens, illustrating the measures provide similar information about transmission heterogeneity. Our findings suggest antibody response can be used to measure population-level transmission of diverse enteropathogens in serologic surveillance.

Benjamin F Arnold, Diana L Martin, Jane Juma, Harran Mkocha, John B Ochieng, Gretchen M Cooley, Richard Omore, E Brook Goodhew, Jamae F Morris, Veronica Costantini, Jan Vinjé, Patrick J Lammie, Jeffrey W Priest. Elife. 2019 Aug 19;8. pii: e45594. doi: 10.7554/eLife.45594.