Molecules with carbon-phosphorus (C-P) bonds are found on the surface of many cells but their biological role is not known. In Tetrahymena thermophila, 60% of phosphorus in the flagellar lipid is covalently bound to carbon as 2-aminoethylphosphonate (AEP). This makes T. thermophila an ideal model to understand the cellular role of AEP as the most common natural C-P molecule. Our preliminary data and the literature posit that AEP synthesis is linked to core mitochondrial metabolism and cell surface interactions. In this project, we aim to identify the interactome of AEP biosynthesis and its importance for mitochondrial function and cell physiology. To do this, we will generate knockout and knockdown mutants in AEP biosynthesis, identify interacting proteins, and dissect how AEP synthesis links to mitochondrial metabolism and phenotype changes in mutant physiology and behaviour. The findings will connect early biochemical studies on AEP with molecular genetics and help to understand the strikingly neglected role of C-P molecules in cells and cell evolution.