Diaminopimelic Acid in the Mu Particles of Paramecium aurelia

Abstract

Mu particles, found in the cytoplasm of Paramecium aurelia, stock 540, syngen 1, are responsible for the mate killing effect of this stock on other syngen 1 stocks after conjugation with them¹. The particles are visible in the phase contrast microscope as rods 2–5µ × 10.5µ in size, and several thousand may be present in the cytoplasm of a single animal. Beale and Jurand² carried out a cytochemical and electron microscope study of these particles and suggested that they were probably bacterial in nature. Van Wagtendonk, Clark and Godoy³ succeeded in growing the lambda particle of stock 299 (syngen 4) in a complex medium outside the host cell, thus clearly showing that this particle was a symbiont inside the Paramecium. It will be shown here that the mu particle is a bacterium in a similar situation, because the analysis of isolated particles has shown the presence of α-ε-diaminopimelic acid (DAP), and possibly of muramic acid; these are compounds typical of the bacterial cell wall⁴.