Activity, regulation and evolution of carbohydrate-active enzymes used in cell wall penetration by unicellular predators and parasitoids of microalgae

• Applicant: Professor Dr. Sebastian Hess
• Subject Area: Animal Physiology and Biochemistry ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 417585753

There is a diversity of parasitoid microbes that attack microalgae and fungi in aquatic and terrestrial ecosystems, forming an integral part of the microbial food web. As suggested by environmental sequencing, many of these highly-specialised interactions are still poorly known. This applies in particular to algivorous protoplast feeders, phagotrophic microeukaryotes that perforate the cell walls of algae and consume the cell contents. During the past years we made progress in understanding the phylogenetic diversity, cellular structure and ecology of protoplast feeders. However, it is still unclear how exactly protoplast feeders recognise their prey and perforate the prey cell wall. Transcriptomic data about the viridiraptorid amoeboflagellate Orciraptor agilis (Rhizaria) suggest that carbohydrate-active enzymes (CAZymes) mediate binding to the prey cell wall and cell wall dissolution. The protein sequences of these CAZymes represent an ideal basis for taking the next experimental steps, to establish a refined model of how protoplast feeders recognise and perforate the cell walls of their prey. Employing heterologous expression systems, we will produce recombinant candidate CAZymes and assay their activity on artificial and natural substrates. To establish the cellular localisation of these proteins in Orciraptor, antibodies will be raised and used for immunofluorescence microscopy. Furthermore, we will investigate the evolution of protoplast feeders by exploring the transcriptomes of the bacterivorous relatives of Orciraptor, specifically screening for cellulases and carbohydrate-binding proteins. Finally, we will expand our research to the vampyrellid amoebae to study how these versatile predatory amoebae adapted to diverse prey types. We will compare the feeding ecology and CAZyme expression in a wide phylogenetic framework and test with differential expression analyses if generalist vampyrellids regulate CAZyme expression in response to the prey cell wall biochemistry. By comparing the molecular toolkit of protoplast feeders of several distant phylogenetic lineages, we will finally understand how this fascinating feeding strategy evolved several times independently in the tree of life.

• DFG Programme: Independent Junior Research Groups