Formation and maturation of phagosomes labeled by magnetic micro particles: an ultrastructural study in Tetrahymena thermophila

Phagosomes of Tetrahymena thermophila were pulse-chase labeled with colloidal magnetic iron-starch particles. These labeled phagosomes are easily purified by magnets in large quantities. They allow us to analyse their biochemical composition which is expected to change stage-specifically during their maturation. Although preliminary observations had shown that these phagosomes are processed similar to phagosomes labeled with food bacteria, we decided to prove the observations at the ultrastructural level. In addition we used phagosomes isolated at defined stages of maturation to study the distribution and number of the intramembrane particles by freeze-fracturing. As no significant differences in processing of phagosomes labeled with bacteria or iron-starch particles were observed, the biochemical data obtained from analysis of magnetically isolated phagosomes will most probably correspond to their authentic composition.