ULTRASTRUCTURE AND DISTRIBUTION OF AN INTRACELLULAR BACTERIUM-LIKE MICROORGANISM IN TISSUES OF LARVAE OF THE SOYBEAN CYST NEMATODE, HETERODERA-GLYCINES

Ultrastructural studies of the anterior region of second-stage larvae of the soybean cyst nematode, Heterodera glycines Ichinohe, revealed the presence of a bacterium-like microorganism within various tissues. The microorganism is found throughout most of the tissues of the larva but especially in the sarcoplasm of the stylet protractor and median bulb muscles, and in the highly reticulate and ribosome-rich tissues of the esophageal glands. The intimate contact between the microorganism and the host nuclei and the presence of parallel arrays of rough endoplasmic reticulum of the host cytoplasm indicate that there may be a mutualistic relationship. However, the microorganisms seem damaged by microbodies in the esophageal gland. The microorganism is rod shaped with average dimensions of 0.4 × 1.8 μm. Both the outer wall, about 9 nm thick, and the plasma membrane, about 7 nm thick, are trilaminar. These membranes are separated by a space of variable width. Rod or tubular structures, about 14-17 nm in diameter, extend from the plasma membrane into the cytoplasm or even right across the width of the cell. © 1979 Academic Press, Inc.