BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Transmission electron micrograph (TEM) of endonuclear bacteria. Nucleus showing nuclear envelope, chromosomes, nucleoplasm and bacteria in the euglenoid Trachelomonas. The endonuclear bacteria (blue) cluster around the central nucleolus, whereas the cytoplasmic bacteria lie among the ribosomes, mitochondria (red) and Golgi bodies. All the bacteria are encapsulated, but do not fix nitrogen and do not appear to have either a symbiotic or parasitic relationship with the host cell; they have apparently acquired an unusual ecological niche without aiding or harming the host (though they must be withdrawing nutrients) and divide to keep pace with host cell and nuclear division. Magnification 30,000x.
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