On the basis of 16S-23S ribosomal DNA analyses, the whitefly Bemisia tabaci (Sternorrhyncha, Aleyrodidae) and the eriococcid Eriococcus spurius (Sternorrhyncha, Eriococcidae) were each found to harbor novel related chlamydial species within the family Simkaniaceae. The generic designation Fritscheagen. nov. is proposed to accommodate the two species, F. bemisiaesp. nov. and F. eriococci sp. nov. The finding of chlamydial 16S-23S ribosomal DNA in B. tabaci is consistent with a previous electron microscopy study which found that bacteriocytes of this species contain structures that we consider to resemble the elementary and reticulate bodies of chlamydia (Costa HS, Westcot DM, Ullman DE, Rosell R, Brown JK, Johnson MW. Protoplasma 189:194-202, 1995). The cloning and sequencing of a 16.6 kilobase DNA fragment from F. bemisiae indicated that it contains six genes encoding for proteins similar to those found in other species of chlamydia. These results extend the range of organisms that harbor chlamydia.
Mealybugs (Hemiptera, Coccoidea, Pseudococcidae), like aphids and psyllids, are plant sap-sucking insects that have an obligate association with prokaryotic endosymbionts that are acquired through vertical, maternal transmission. We sequenced two fragments of the genome of Tremblaya princeps, the endosymbiont of mealybugs, which is a member of the  subdivision of the Proteobacteria. Each of the fragments (35 and 30 kb) contains a copy of 16S-23S-5S rRNA genes. A total of 37 open reading frames were detected, which corresponded to putative rRNA proteins, chaperones, and enzymes of branched-chain amino acid biosynthesis, DNA replication, protein translation, and RNA synthesis. The genome of T. princeps has a number of properties that distinguish it from the genomes of Buchnera aphidicola and Carsonella ruddii, the endosymbionts of aphids and psyllids, respectively. Among these properties are a high G؉C content (57.1 mol%), the same G؉C content in intergenic spaces and structural genes, and similar G؉C contents of the genes encoding highly and poorly conserved proteins. The high G؉C content has a substantial effect on protein composition; about one-third of the residues consist of four amino acids with high-G؉C-content codons. Sequence analysis of DNA fragments containing the rRNA operon and adjacent regions from endosymbionts of several mealybug species suggested that there was a single duplication of the rRNA operon and the adjacent genes in an ancestor of the present T. princeps. Subsequently, in one mealybug lineage rpS15, one of the duplicated genes, was retained, while in another lineage it decayed. These results extend the diversity of the types of endosymbiotic associations found in plant sap-sucking insects.Mealybugs (Hemiptera, Coccoidea, Pseudococcidae) are plant sap-sucking insects which have a novel symbiotic association (20,21,47,48). Within the body cavity of the insect is a large multicellular structure called a bacteriome that is made up of cells called bacteriocytes. Within the bacteriocytes are host-derived vesicles containing the gram-negative primary endosymbiont Tremblaya princeps (48; M. Thao, P. J. Gullan, and P. Baumann, submitted for publication). This organism is a member of the  subdivision of the Proteobacteria (35;Thao et al., submitted). Remarkably, T. princeps may harbor within its cells other gram-negative bacteria (secondary endosymbionts) belonging to the ␥ subdivision of the Proteobacteria (18, 48; Thao, submitted). Recently, using 16S-23S ribosomal DNA (rDNA) sequences, we have examined the evolutionary relationships of T. princeps from 22 species of mealybugs and the secondary endosymbionts from 12 of these species. The results suggest that the symbiotic association between T. princeps and mealybugs is a result of a single infection of an insect host 100 to 200 million years ago (Thao et al., submitted). In contrast to this result, it appears that infection of T. princeps with different precursors of the secondary endosymbionts occurred multiple times and that following infec...
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