Efficient generation of mNeonGreen Plasmodium falciparum reporter lines enables quantitative fitness analysis

The PfK13 G533S mutation confers artemisinin partial resistance in multiple genetic backgrounds of Plasmodium falciparum

Mutations in the Plasmodium falciparum Kelch 13 (PfK13) protein are the key determinant of artemisinin partial resistance. While more than 200 PfK13 mutations have been identified in global parasite populations, only 13 have been validated to confer in vivo or in vitro artemisinin partial resistance. In the western Greater Mekong Subregion, the prevalence of the PfK13 G533S mutation has significantly increased in recent years. Field isolates carrying the PfK13 G533S mutation showed slower parasite clearance and higher day-3 positivity rates after artemisinin treatment, while culture-adapted isolates displayed significantly elevated ring-stage survival rates. Here, the PfK13 G533S mutation was introduced using CRISPR/Cas9 into four parasite strains: Dd2, 3D7, GB4, and F09N25 (a recent culture-adapted field isolate from the China-Myanmar border area). Across all four genetic backgrounds, the PfK13 G533S mutation conferred ring-stage survival rates of 12%-23% with a minimal fitness cost, explaining its rising prevalence in the region. In contrast, the PfK13 G533A mutation, sporadically detected in world P. falciparum populations, did not increase ring-stage survival rates when engineered into the 3D7 and Dd2 strains. These findings validate the PfK13 G533S mutation as a critical marker for artemisinin resistance surveillance and underscore the importance of monitoring its spread.

Expanding the fluorescent toolkit: Blue fluorescent protein-expressing Plasmodium berghei for enhanced multiplex microscopy

Fluorescent proteins are widely used as markers to differentiate genetically modified cells from their wild-type counterparts. In malaria research, the prevalent fluorescent markers include red fluorescent proteins (RFPs) and their derivatives, such as mCherry, along with green fluorescent proteins (GFPs) and their derivatives. Recognizing the need for additional fluorescent markers to facilitate multiplexed imaging, this study introduced parasite lines expressing blue fluorescent protein (BFP). These lines enable simultaneous microscopy studies of proteins tagged with GFP, RFP, or detected by fluorophore-labeled antibodies, enhancing the analysis of complex biological interactions. Expression of BFP throughout the parasite's life cycle was driven by the robust Hsp70 promoter, ensuring stable, detectable protein levels suitable for fluorescent light analysis methods, including flow cytometry and fluorescent microscopy. We generated two Plasmodium berghei (P. berghei) lines expressing cytosolic BFP through double crossover homologous recombination targeting the silent 230p locus: eBFP2 (PbeBFP2) and mTagBFP2 (PbmTagBFP2). We compared these transgenic lines to established mCherry-expressing parasites PbmCherryHsp70 (PbmCherry) across their life cycles. The PbmTagBFP2 parasites exhibited fluorescence approximately 4.5 times brighter than the PbeBFP2 parasites in most life cycle stages. Both BFP-expressing lines developed normally through the entire parasite life cycle, offering a valuable expansion to the toolkit for studying Plasmodium biology at the host-pathogen interface.

Imaging malaria parasites across scales and time

The idea that disease is caused at the cellular level is so fundamental to us that we might forget the critical role microscopy played in generating and developing this insight. Visually identifying diseased or infected cells lays the foundation for any effort to curb human pathology. Since the discovery of the Plasmodium-infected red blood cells, which cause malaria, microscopy has undergone an impressive development now literally resolving individual molecules. This review explores the expansive field of light microscopy, focusing on its application to malaria research. Imaging technologies have transformed our understanding of biological systems, yet navigating the complex and ever-growing landscape of techniques can be daunting. This review offers a guide for researchers, especially those working on malaria, by providing historical context as well as practical advice on selecting the right imaging approach. The review advocates an integrated methodology that prioritises the research question while considering key factors like sample preparation, fluorophore choice, imaging modality, and data analysis. In addition to presenting seminal studies and innovative applications of microscopy, the review highlights a broad range of topics, from traditional techniques like white light microscopy to advanced methods such as superresolution microscopy and time-lapse imaging. It addresses the emerging challenges of microscopy, including phototoxicity and trade-offs in resolution and speed, and offers insights into future technologies that might impact malaria research. This review offers a mix of historical perspective, technological progress, and practical guidance that appeal to novice and advanced microscopists alike. It aims to inspire malaria researchers to explore imaging techniques that could enrich their studies, thus advancing the field through enhanced visual exploration of the parasite across scales and time.

Reporter parasite lines: valuable tools for the study of Plasmodium biology

The human malaria parasite Plasmodium falciparum causes the most severe form of malaria in endemic regions and is transmitted via mosquito bites. To better understand the biology of this deadly pathogen, a variety of P. falciparum reporter lines have been generated using transgenic approaches to express reporter proteins, such as fluorescent proteins and luciferases. This review discusses the advances in recently generated P. falciparum transgenic reporter lines, which will aid in the investigation of parasite physiology and the discovery of novel antimalarial drugs. Future prospects for the generation of new and superior human malaria parasite reporter lines are also discussed, and unresolved questions in malaria biology are highlighted to help boost support for the development and implementation of malaria treatments.

Let it glow: genetically encoded fluorescent reporters in Plasmodium

The use of fluorescent proteins (FPs) in Plasmodium parasites has been key to understand the biology of this obligate intracellular protozoon. FPs like the green fluorescent protein (GFP) enabled to explore protein localization, promoter activity as well as dynamic processes like protein export and endocytosis. Furthermore, FP biosensors have provided detailed information on physiological parameters at the subcellular level, and fluorescent reporter lines greatly extended the malariology toolbox. Still, in order to achieve optimal results, it is crucial to know exactly the properties of the FP of choice and the genetic scenario in which it will be used. This review highlights advantages and disadvantages of available landing sites and promoters that have been successfully applied for the ectopic expression of FPs in Plasmodium berghei and Plasmodium falciparum. Furthermore, the properties of newly developed FPs beyond DsRed and EGFP, in the visualization of cells and cellular structures as well as in the sensing of small molecules are discussed.

Drug resistance and vaccine target surveillance of Plasmodium falciparum using nanopore sequencing in Ghana

Malaria results in over 600,000 deaths annually, with the highest burden of deaths in young children living in sub-Saharan Africa. Molecular surveillance can provide important information for malaria control policies, including detection of antimalarial drug resistance. However, genome sequencing capacity in malaria-endemic countries is limited. We designed and implemented an end-to-end workflow to detect Plasmodium falciparum antimalarial resistance markers and diversity in the vaccine target circumsporozoite protein (csp) using nanopore sequencing in Ghana. We analysed 196 clinical samples and showed that our method is rapid, robust, accurate and straightforward to implement. Importantly, our method could be applied to dried blood spot samples, which are readily collected in endemic settings. We report that P. falciparum parasites in Ghana are mostly susceptible to chloroquine, with persistent sulfadoxine-pyrimethamine resistance and no evidence of artemisinin resistance. Multiple single nucleotide polymorphisms were identified in csp, but their significance is uncertain. Our study demonstrates the feasibility of nanopore sequencing for malaria genomic surveillance in endemic countries.