ASP Online Seminar Series: 19th July 2024 @ 1pm AEST

Capella Maguire undertook her Honours project in the ANU Toxo Lab supervised by Assoc. Prof. Giel van Dooren. She explored the role of the mitochondrion in central carbon metabolism in the apicomplexan parasite Toxoplasma gondii. Her Honours work raised several new questions about the exact nature of metabolic pathways in the parasite. Intrigued to find some answers she continued as a PhD student in the van Dooren Group. Capella’s PhD is focused on mitochondrial metabolism in T. gondii primarily investigating the TCA cycle and its integration with key cytosolic metabolic pathways.

Toxoplasma gondii is an apicomplexan parasite that causes severe disease in immunocompromised individuals, newborns, and livestock. This ubiquitous parasite uses central carbon metabolism pathways to generate energy and macromolecules for its proliferation and survival. In other eukaryotes, the mitochondrial tricarboxylic acid (TCA) cycle plays a key role in energy generation and the provision of biosynthetic intermediates. T. gondii harbours a complete functional mitochondrial TCA cycle, but the enzymes that catalyse the individual metabolic reactions remain understudied, and the overall importance of the TCA cycle is still uncertain. To address this knowledge gap, we investigated the importance and role of the TCA cycle in T. gondii, using a combination of forward and reverse genetics as well as physiological and metabolomic analyses. We found that the loss of some TCA cycle reactions led to severe defects in parasite proliferation and mitochondrial oxygen consumption in vitro, whereas loss of others had minimal impact. Using CRISPR/Cas9 genome-wide screening of TCA cycle mutants we discovered the presence of several functional redundancies. One notable redundancy was in the reactions catalysed by the mitochondrial TCA cycle enzyme malate:quinone oxidoreductase (MQO) and the cytosolic enzyme malate dehydrogenase (MDH), both of which mediate malate oxidation but in different subcellular compartments. Parasites which simultaneously lack both MQO and MDH exhibited a defective TCA cycle, impaired pyrimidine biosynthesis and accumulation of fumarate. We are currently investigating the essential metabolic process(es) that require malate oxidation in the parasite. Overall, our findings enhance the understanding of a key metabolic pathway and the flexible nature of central carbon metabolism in T. gondii.

Lizenn Delisle is a shellfish physiologist in the Aquatic animal health team at Cawthron Institute, New Zealand. She is a passionate marine scientist working on diseases in aquaculture and physiology of marine invertebrates. Currently, her research aims to identify pathogens associated with severe mortality episodes occurring on aquaculture species in New Zealand and their mechanisms of infection through the analyses of field samples, experimental infection in laboratory and in vitro propagation. Her research also focuses on mechanisms of host response to infection, by using large scale molecular approaches like transcriptomic, metabarcoding or proteomic and targeted analyses (PCR, qPCR) to improve understanding of shellfish resilience to pathogens which will support the aquaculture industry.

“Health Challenges in Aquaculture: A Perkinsus olseni in Green-lipped Mussel case study.”

Perkinsus olseni is a protozoan parasite that infects a wide variety of molluscs and gastropods. Regularly associated with mass mortality events, P. olseni causes signficant economic losses in the aquaculture sector worldwide. P. olseni was first identified in New Zealand in clams from the Mangamangaroa stream near Auckland in May 2000. It rapidly spread to other shellfish species such as cockles and abalone in the North Island in 2001 and was first detected in the South Island in 2014, in Green-lipped mussels (GLM, Perna canaliculus). The presence of the parasite has never been clearly associated with large GLM mortality events. However it is regularly detected in young GLM and adults where it preferentially develops in the mantle, palps and gills. No gross pathology such as pustules are associated with Perkinosis, but histopathological examination of infected adult GLM reveals focal hemocytosis and hemocyte apoptosis and necrosis surrounding the parasite. The emergence of P. olseni in commercially important species such as Green-lipped mussel is a major concern, and further investigations are needed to assess the risk associated with this parasite for aquaculture industry. Using infected mussels collected in Nelson Bay, we established for the first-time an in-vitro culture of P. Olseni from Green-lipped mussel enabling the description of the parasite’s life cycle and the definition of its thermal optimum. Our team recently conducted our first experimental infection in adult and juvenile Greenshell™ mussels providing valuable data on the disease progression and on the infectivity of the different Perkinsus life stages.

Our ASP Online Seminar Series image is created by Thorey Jonsdottir.