Empirical evidence of the host–parasite arms race
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Metabolic crosstalk between the mitochondrion and the nucleus is essential for Toxoplasma gondii infection
Toxoplasma gondii, an intracellular pathogenic protist with a remarkable ability to infect a wide range of host cells, displays an equally exceptional design of its carbon metabolism. There are, however, critical gaps in our understanding of the metabolic network in T. gondii. We characterized the mito-nuclear metabolism and organelle coupling during its acute infection (lytic cycle). The major enzymes of the TCA cycle, i.e., citrate synthase (CS1), succinyl-CoA synthase alpha subunit (SCSα), succinate dehydrogenase (SDHA) and FAD malate dehydrogenase (MDH-FAD) located in the parasite mitochondrion support its asexual reproduction but are not needed for its survival. The SCSα and SDHA mutants are nearly avirulent in a mouse model, and they can protect the host against a lethal challenge infection. Genetic deletion of MDH-FAD dysregulated glucose-derived carbon flux, leading to a collapse of the mitochondrial membrane potential. The parasite also harbors a cytosolic isoform of MDH and a nuclear malic enzyme (ME) contributing to malate oxidation; however, only the latter is essential for the lytic cycle. Expression of ME in the nucleus is crucial for the parasite development. Besides, conditional knockdown of ME impairs the histone acetylation and disrupts the expression of several genes in tachyzoites. Our work discloses novel network design features of T. gondii and highlights the therapeutic and vaccination potential of the parasite metabolism.
Genome-wide gene expression profiles throughout human malaria parasite liver stage development in humanized mice
Gene expression of Plasmodium falciparum (Pf) liver-stage (LS) parasites has remained poorly characterized, although they are major vaccine and drug targets. Using a human liver-chimaeric mouse model and a fluorescent parasite line (PfNF54CSPGFP), we isolated PfLS and performed transcriptomics on key LS developmental phases. We linked clustered gene expression to ApiAP2, a major family of transcription factors that regulate the parasite life cycle. This provided insights into transcriptional regulation of LS infection and expression of essential LS metabolic and biosynthetic pathways. We observed expression of antigenically variant PfEMP1 proteins and the major Pf protein export machine PTEX and identified protein candidates that might be exported by LS parasites. Comparing Pf and P. vivax LS transcriptomes, we uncovered differences in their expression of sexual commitment factors. This data will aid LS research and vaccine and drug target identification for prevention of malaria infection.
Interracial contact shapes racial bias in the learning of person-knowledge
During impression formation, perceptual cues facilitate social categorization while person-knowledge can promote individuation and enhance person memory. Although there is extensive literature on the cross-race recognition deficit, observed when racial ingroup faces are recognized more than outgroup faces, it is unclear whether a similar deficit exists when recalling individuating information about outgroup members. To better understand how perceived race can bias person memory, the present study examined how self-identified White perceivers’ interracial contact impacts learning of perceptual cues and person-knowledge about perceived Black and White others over five sessions of training. While person-knowledge facilitated face recognition accuracy for low-contact perceivers, face recognition accuracy did not differ for high-contact perceivers based on person-knowledge availability. The results indicate a bias towards better recall of ingroup person knowledge, which decreased for high-contact perceivers across the five-day training but simultaneously increased for low-contact perceivers. Overall, the elimination of racial bias in recall of person-knowledge among high-contact perceivers amid a persistent cross-race deficit in face recognition suggests that contact may have a greater impact on the recall of person-knowledge than on face recognition.
The succession of epiphytic microalgae conditions fungal community composition: how chytrids respond to blooms of dinoflagellates
This study aims to investigate the temporal dynamics of the epiphytic protist community on macroalgae, during the summer months, with a specific focus on fungi, and the interactions between zoosporic chytrid parasites and the proliferation of the dinoflagellates. We employed a combination of environmental sequencing techniques, incubation of natural samples, isolation of target organisms and laboratory experiments. Metabarcoding sequencing revealed changes in the dominant members of the epiphytic fungal community. Initially, fungi comprised < 1% of the protist community, mostly accounted for by Basidiomycota and Ascomycota, but with the emergence of Chytridiomycota during the mature phase of the biofilm, the fungal contribution increased to almost 30%. Chytridiomycota became dominant in parallel with an increase in the relative abundance of dinoflagellates in the community. Microscopy observations showed a general presence of chytrids following the peak proliferation of the dinoflagellate Ostreopsis sp., with the parasite, D. arenysensis as the dominant chytrid. The maximum infection prevalence was 2% indicating host-parasite coexistence. To further understand the in-situ prevalence of chytrids, we characterised the dynamics of the host abundance and prevalence of chytrids through co-culture. These laboratory experiments revealed intraspecific variability of D. arenysensis in its interaction with Ostreopsis, exhibiting a range from stable coexistence to the near-extinction of the host population. Moreover, while chytrids preferentially parasitized dinoflagellate cells, one of the strains examined displayed the ability to utilize pollen as a resource to maintain its viability, thus illustrating a facultative parasitic lifestyle. Our findings not only enrich our understanding of the diversity, ecology, and progression of epiphytic microalgal and fungal communities on Mediterranean coastal macroalgae, but they also shed light on the presence of zoosporic parasites in less-explored benthic habitats.
Pathogens and planetary change
Emerging infectious diseases, biodiversity loss, and anthropogenic environmental change are interconnected crises with massive social and ecological costs. In this Review, we discuss how pathogens and parasites are responding to global change, and the implications for pandemic prevention and biodiversity conservation. Ecological and evolutionary principles help to explain why both pandemics and wildlife die-offs are becoming more common; why land-use change and biodiversity loss are often followed by an increase in zoonotic and vector-borne diseases; and why some species, such as bats, host so many emerging pathogens. To prevent the next pandemic, scientists should focus on monitoring and limiting the spread of a handful of high-risk viruses, especially at key interfaces such as farms and live-animal markets. But to address the much broader set of infectious disease risks associated with the Anthropocene, decision-makers will need to develop comprehensive strategies that include pathogen surveillance across species and ecosystems; conservation-based interventions to reduce human–animal contact and protect wildlife health; health system strengthening; and global improvements in epidemic preparedness and response. Scientists can contribute to these efforts by filling global gaps in disease data, and by expanding the evidence base for disease–driver relationships and ecological interventions.
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