The Bacteroidetes Blattabacterium and Sulcia as Primary Endosymbionts of Arthropods

The study of intracellular microorganisms harbored by arthropods, particularly by insects, began in the second half of the nineteenth century, following the wider use of light microscopy. It was only at the end of the century, however, that Blochmann (1887) observed peculiar structures in cells of the fat body of cockroaches, cells that are now known as bacteriocytes (Sacchi et al. 1988). Bacteriocytes are cells specialized to harbor obligatory beneficial symbionts in insects. At the beginning of the twentieth century, Karel Sulc (1910, 1924) described aggregations of bacteriocytes (bacteriomes) in the body cavity of cicads, while Carlo Jucci (1932) observed bacteriocytes in the fat body of the termite Mastotermes darwiniensis. Jucci recognized the similarity between this type of cell in M. darwiniensis and those present in the fat body of cockcroaches. These three scientists (Blochmann, Sulc, and Jucci) thus reported the first observations of the bacterial symbionts that are now known to belong to the Bacteroidetes phylum. The work of Blochmann, Sulc, and Jucci is reviewed in detail in Buchner (1965).