Reproduction and morphogenesis of Rickettsiella chironomi, an unusual intracellular procaryotic parasite of midge larvae.

The reproduction and morphogenesis of Rickettsiella chironomi, an unusual procaryotic parasite of midge larvae, was studied with electron microscopy. The morphogenic cycle was similar to that found in chlamydia and consisted of four major cell types: (i) medium-sized spherical initial bodies (ca. 1 micrometers in diameter), (ii) large spherical initial bodies (1.5-2 micrometers), (iii) spherical intermediate bodies (600 to 700 nm), and (iv) disk-shaped elementary bodies (60 X 600 nm). The primary mode of reproduction involved binary fission of initial bodies to form other initial bodies or intermediate bodies. Each intermediate body condensed, forming an elementary body. The morphogenesis of R. chironomi is compared with that of several other organisms to which it is possibly related, including vertebrate chlamydia and invertebrate pathogens of the genera Rickettsiella and Porochlamydia, and its taxonomic position in regard to these is discussed. Additionally, a brief description of the pathology caused by the development of R. chironomi in larvae of Chironomus decorus and Chironomus frommeri is given.