Ultrastructure of Flagellated Lambda Symbionts in Paramecium aurelia

SUMMARY: The symbionts called ‘lambda’ present in the cytoplasm of killer stocks 239 (syngen 4) and 299 (syngen 8) of Paramecium aurelia have been investigated. Observations with the electron microscope of ultrathin sections and of negatively stained material revealed that these symbionts have peritrichous flagellation. The ultrastructures of symbionts from both stocks were identical and were those of flagellated bacteria.