cell surface, endosymbiosis, Escherichia coli,
A logical prerequisite for establishing endosymbiotic relationships in ciliates is evading digestion and later escaping from food vacuoles of the host by food bacteria. With the technique described in this report, we provide a versatile experimental model that allows defining biochemical and biophysical surface properties of food bacteria, enabling them to evade digestion in feeding experiments. By chemical coupling with the carbodiimide EDAC [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide], any substance carrying amino- or carboxyl groups can be added covalently to the bacteria’s surface and, in consequence, change the surface properties in a predetermined manner. For modification, two different transformant strains of Escherichia coli were used, either expressing red or green fluorescent protein, to follow their fate after uptake by Tetrahymena pyriformis by fluorescence microscopy. The viability of E. coli is not severely impaired by the modification process itself. Sufficient amounts of cells remain viable for feeding. The number of viable cells remains constant over two days of storage in the refrigerator. This technique offers the additional advantage to be experimentally facile and much faster and more versatile than approaches based on constructing defined surface mutants.