xenosome

{{Short description|Bacterium that lives in the body of some marine protozoans}}

A xenosome is a bacterium that lives in the body of some marine protozoans. It primarily refers to bacterial invaders of the cytoplasm of a single genus of marine scuticociliates.{{Cite journal |last=Corliss |first=John O. |date=August 1985 |title=Concept, Definition, Prevalence, and Host‐Interactions of Xenosomes (Cytoplasmic and Nuclear Endosymbionts) 1, 2 |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1550-7408.1985.tb04030.x |journal=The Journal of Protozoology |language=en |volume=32 |issue=3 |pages=373–376 |doi=10.1111/j.1550-7408.1985.tb04030.x |issn=0022-3921}} They are found in ciliates, sometimes with a methanogenic role inside anaerobic ciliates.{{cite book|first1=Michael|last1=Levandowsky|chapter=Physiological Adaptations of Protists|title=Cell Physiology Sourcebook: Essentials of Membrane Biophysics|editor-first1=Nicholas|editor-last1=Sperelakis|edition=Fourth|publication-place=Amsterdam; Boston|publisher=Elsevier/AP|date=2012|pages=874–890|isbn=978-0-12-387738-3}}

In 1985, researcher John Corliss proposed to expand the definition of the term to include all DNA-containing, membrane-bounded bodies or organelles—prokaryotic or eukaryotic in original nature—found within the cytoplasm or nucleus of eukaryotic cells of any or all kinds, regardless of whether the occupation was temporary or permanent.