Biology subjects

Kals, E.

Publications and source records attributed to Kals, E..

5 recordsLinked to original sources

bioRxiv2026

A combinatorial genetics approach reveals limits to redundancy within Plasmodium falciparum invasion ligand families

To maintain infection in the human bloodstream, Plasmodium falciparum parasites undergo repeated cycles of invasion of and multiplication inside red blood cells (RBCs). Two protein families, the Erythrocyte binding-like (EBA) and Reticulocyte binding-like (Rh) proteins, are known to play a key role in invasion, mediating early stages of attachment of the P. falciparum merozoite to the host RBC. There is a degree of redundancy within these families, such that disrupting the function of individual EBA/Rh proteins in vitro is not sufficient to prevent invasion. By employing a novel approach to disrupt multiple EBA and Rh genes in combination, we systematically assessed functional interdependency across these families for the first time. This analysis, and further characterisation of mutant parasites, revealed that disruption of some pairs of EBA/Rh ligands significantly impacted P. falciparum invasion, whereas others did not. Disruption of PfEBA175 in combination with either PfRh2b or PfRh4 significantly reduced parasite multiplication in vitro, indicating that the remaining EBA/Rh proteins could not fully compensate for the absence of these three key invasion ligands. PfEBA175, PfRh2b and PfRh4 may therefore represent a critical nexus of the parasite invasion machinery, and combinatorial approaches that target these specific ligands could be a beneficial therapeutic approach.

microbiology↗

bioRxiv2025

Microfluidic Platform for Automatic Quantification of Malaria Parasite Invasion Under Physiological Flow Conditions

Understanding the impact of forces generated by blood flow on biological processes in the circulatory system, such as the invasion of human red blood cells by malaria parasites, is currently limited by the lack of experimental systems that integrate them. Recent systematic quantification of the growth of Plasmodium falciparum, the species that causes the majority of malaria mortality, under a range of shaking conditions has shown that parasite invasion of erythrocytes is affected by the shear stress to which the interacting P. falciparum merozoites and their target red blood cells are exposed. Blood flow could similarly impact shear stress and therefore invasion in vivo, but there is currently no method to test the impact of flow-induced forces on parasite invasion. We have developed a microfluidic device with four channels, each with dimensions similar to those of a post-capillary venule, but with different flow velocities. Highly synchronised P. falciparum parasites are injected into the device, and parasite egress and invasion rates are quantified using newly developed custom video analysis, which fully automates cell type identification and trajectory tracking. The device was tested with both wild-type P. falciparum lines and lines in which genes encoding proteins involved in parasite invasion had been deleted. Deletion of Erythrocyte Binding Antigen 175 (PfEBA175) has a significant impact on invasion under flow, but not in static culture. These findings establish for the first time that flow conditions can critically affect parasite invasion in a genotype-dependent manner. The method can be applied to other biological processes affected by fluid motion, such as cell adhesion, migration, and mechanotransduction.

microbiology↗

bioRxiv2024

Growing Malaria Parasites at a Critical Shaking Speed Mimicking Physiological Flow Reveals New Phenotypes for Invasion Ligands

Malaria kills over 600,000 people annually, with all the clinical symptoms being caused by the blood stage of the infection. Malaria parasites invade red blood cells (RBCs), where they grow and multiply until daughter parasites egress to invade new RBCs. This cycle happens primarily in the blood circulation, bone marrow, and spleen, where parasites and RBCs are exposed to flow-generated forces. Despite this, almost all in vitro growth assays are carried out in static conditions, which are a poor mimic for the conditions that malaria parasites encounter in the body. Therefore, we systematically tested the impact of dynamic conditions created by orbital shaking platforms on parasite growth and explored the link between growth and the wall shear stress forces generated by fluid motion. For several strains of the deadliest malaria species, Plasmodium falciparum, we showed that strikingly, for any given vessel, there is a critical shaking speed at which growth rates are reduced, corresponding to when the RBCs start to aggregate in the centre of the well, before growth increases again at higher shaking speeds. The force that parasites are exposed to at this critical shaking speed corresponds cloesly with previous measurements for the forces that RBCs and parasites are exposed to in the microvasculature. During invasion, the early attachment of the parasites to RBCs is dependent on two families of attachment proteins, the Erythrocyte Binding Antigen (PfEBA) family and the Reticulocyte Binding Protein Homologue (PfRH) family, which are thought to be largely redundant in function. We used a panel of PfEBA and PfRH knock-out lines to show for the first time that several of these ligands have greater importance in high wall shear stress conditions. This both adds new understanding to the function of these ligand families, and indicates that the concept of the critical shaking speed can reveal new parasite growth phenotypes.

microbiology↗

bioRxiv2024

Antibiotics change the growth rate heterogeneity and morphology of bacteria

A better understanding of the system-level effects of antibiotics is necessary to fight the rise of antibiotic resistance. Utilising the Multipad Agarose Plate (MAP), we monitor the growth rate and cell morphology of three clinically relevant species (E.coli, S.aureus and P.aeruginosa) after exposure to 11 different concentrations of 13 antibiotics (for a total of 24 microbe-antibiotic combinations). As the drug dose approaches the MIC and regardless of the mode of action, our results show a consistent increase in growth rate heterogeneity. Remarkably, drugs that affect protein synthesis consistently show the opposite trend, reducing heterogeneity. We hypothesize that growth rate heterogeneity under antibiotic treatment might therefore depend on the functional distance of the target from ribosomal activity, which is key in determining growth rate. Low heterogeneity is desirable from a clinical perspective, as the opposite is often associated to persistence and antibiotic survival. For all of the antibiotics and species tested, we also find a striking and non-trivial correlation between morphological alterations and growth inhibition. This observation allows us to introduce a new morphological parameter, MOR50, that enables the estimation of minimum inhibitory concentration (MIC) for antibiotic susceptibility testing (AST) with a single snapshot after 2.5 hours of incubation. In addition to introducing a novel, resource-efficient, rapid AST method, our findings shed new light on the effects of antibiotic perturbations on bacteria at the system level that might inform treatment design.

microbiology↗

bioRxiv2024

Optical tweezers reveal that PfEBA and PfRH ligands, not PfMSP1, play a central role in Plasmodium-falciparum merozoite-erythrocyte attachment

Malaria pathogenesis and parasite multiplication both depend on the ability of Plasmodium falciparum merozoites to invade human erythrocytes. Invasion is a complex multi-step process that is known to involve multiple P. falciparum proteins but dissecting the precise role of individual proteins has to date been limited by the availability of quantifiable phenotypic assays. In this study, we apply a new approach to assigning function to invasion proteins by using optical tweezers to directly manipulate recently egressed merozoites and erythrocytes and quantify the strength of attachment between them, as well as the frequency with which such attachments occur. Using a range of inhibitors, antibodies, and genetically modified P. falciparum strains, we quantitated the contribution of individual P. falciparum proteins to these merozoite-erythrocyte attachment phenotypes for the first time. Most of the interactions investigated did not affect the force needed to pull merozoites and erythrocytes apart, including loss of the major P. falciparum merozoite surface protein PfMSP1 and PfGAP45, part of the glideosome actinomyosin motor complex. The only factors that significantly reduced the strength of merozoite-erythrocyte attachment were ones that disrupted the function of members of the EBA-175 like Antigen (PfEBA) family and Reticulocyte Binding Protein Homologue (PfRH) invasion ligand families. While these assays also reinforced the known redundancy within these families, with the deletion of some ligands not impacting detachment force, it appears that the PfEBA/PfRH families play a central role in merozoite attachment, not the major merozoite surface protein PfMSP1. Author summaryMalaria is a devastating disease caused by a parasitic infection. The deadliest species is Plasmodium falciparum, which causes more than 600,000 deaths annually. The parasites life cycle is complex, but all the symptoms of malaria are caused when the parasites replicate in human red blood cells. Replication depends on the invasion of the red blood cells by the parasites which is a complex process involving multiple molecular interactions and multiple steps. Invasion begins with the attachment of the parasite to the red blood cell, making this step of particular interest in the development of new therapeutics. We assessed which interactions are key to the strength of attachment using an optical tweezer assay, which allowed us to directly measure the binding force between individual parasites and red blood cells whilst using a range of molecular and genetic tools that target specific interactions known to have a role in invasion. This showed that loss of a protein commonly thought to be critical to the early stages of binding (PfMSP1) had no effect on attachment strength, whereas disruptions of several members from two families of proteins (the Erythrocyte Binding Like protein family and the reticulocyte binding-like protein family) affect attachment strength.

molecular biology↗