Refractile bodies (R bodies) from the macronuclear killer particle Caedibacter caryophila

Abstract

ABSTRACT The macronuclei of certain isolates of Paramecium caudatum are inhabited by the bacterial endonucleobiont Caedibacter caryophila. These symbionts confer upon host paramecia a killer trait, which is clearly associated with the presence of R bodies in the endosymbionts. R bodies are unique inclusion bodies of caedi-bacteria (which are obligate endosymbionts of Paramecium) and of certain free-living bacteria of the genus Pseudomonas. They have been grouped into four classes on the basis of morphology and behaviour. A fifth R body type, introduced in this study, is named the Cc R body to indicate its presence in bright particles of Caedibacter caryophila. Type Cc R bodies are approximately 0–8 pm in width and diameter. They unroll in a telescopic fashion from the inside and are distinguished by a tapered inner and a blunt outer terminus. They are further associated with icosahedral bacteriophages, which stick to the inner terminus. Cc R body proteins show a ladder-like pattern of stained bands on polyacrylamide gels and exhibit a certain degree of antigenic cross-reactivity with type 51 R bodies.