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pH regulatory systems of marine larvae: new models for gastro-intestinal health and biomineralization in a changing environment

Subject Area Animal Physiology and Biochemistry
Term from 2018 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 403529967
 
Final Report Year 2024

Final Report Abstract

In this project I employed the sea urchin larva, a highly tractable model system that can work from the whole animal level to specific manipulations of the genetic material, to investigate pH regulatory systems relevant for gastro-intestinal-health and biomineralization of the larval skeleton. In the frame of this fife year program my group made exiting new discoveries in the different parts of this project. The first objective addressed the epithelial transport mechanisms that regulate the ionic and pH homeostasis of the midgut. We were able to identify some of the major ion transporters that are responsible to maintain these specific conditions in the larval midgut. Exposure to acidified conditions as predicted for the near future in the frame of the ongoing global change phenomenon ocean acidification (OA) led to a partial reduction in midgut pH that was however compensated by increased ion transport activity to defend midgut homeostasis. This for the first time identified a physiological process that explains a shift in the animal´s energy budget towards compensatory processes leaving less energy for growth and development- a commonly observed phenomenon when organisms are raised under OA conditions. Interestingly, this compensatory reaction was particularly strong when larvae were exposed to a marine pathogen in combination with decreased seawater pH. This finding of the second objective addressing the role of midgut pH as a first line of defense against environmental pathogens confirmed our initial hypothesis that alkaline conditions help to regulate a healthy gut microbiome. Furthermore, we could show that a pharmacological reduction in midgut pH substantially increases the susceptibility of the organisms to a marine pathogen. The third objective, addressed the cellular mechanisms that marine organisms use to generate mineralized shells and skeletons. This part has led to new fundamental discoveries in the cellular physiology of calcifying systems. We identified a proton channel that allows protons that are produced by the mineralization process to exit the cell. However, such a mechanism requires very stable pH conditions and may represent the Achilles heel of marine calcifiers to OA. Furthermore, this project identified a carbon concentration mechanisms in calcifying cells of the sea urchin larva that utilize metabolic CO2 to generate its calcitic skeletons. This project allowed me to develop and consolidate my scientific profile over the course of five years. Based on these findings, in particular the cellular mechanisms of mineralization I was able to generate new scientific venues for future research directions.

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