Light and electron microscopic study of a Rickettsiella species from the cockroach Blatta orientalis

An infection with Rickettsiella sp. was responsible for an illness causing heavy body swelling in the Oriental cockroach Blatta orientalis. Reproducti on of the colony stagnated. Vacuoles with parasitic bacteria occurred mainl y in the fat body, but also in nearly all other organs, such as gut epithel ium, Malpighian tubules, blood cells, and ovarioles. The parasites clearly differed from the symbiotic bacteria of the genus Blattabacterium, which re gularly occur in the mycetocytes of B. orientalis. The vacuoles contained f our stages of Rickettsiella: (1) infectious, electron-dense, rod-like eleme ntary bodies (mean size 300 x 145 nm); (2) an electron-dense, flat intermed ium stage, called hat body (mean size 515 x 255 x 125 nm); (3) an electron- light, spherical intermedium stage, called condensing sphere (mean size 340 nm); portions of cytoplasm condensed crescent-like at the border or in the center of the cell; and (4) large, spherical, electron-light initial bodie s that multiplied by binary fission (mean size 600 nm). The initial bodies had a three-layered cell boundary, but all other stages had a five-layered cell boundary. Elementary and flat bodies contained an electron-light, obli que lamella and an oval structure with an array of ribosome-like granules, respectively. In contrast to other species of Rickettsiella, crystal format ion or multiple division did not occur. The described species of Rickettsie lla is different from "R. blattae," which belongs to the R. popilliae group . Instead, it shares more similarities with the R. chironomi group. To avoi d confusion, it was provisionally named "R. crassificans." (C) 2000 Academi c Press.