The adzuki bean beetle,Callosobruchus chinensis, is triple-infected with distinct lineages ofWolbachiaendosymbiont, wBruCon, wBruOri, and wBruAus, which were identified by theirwsp(Wolbachiasurface protein) gene sequences. Whereas wBruCon and wBruOri caused cytoplasmic incompatibility of the host insect, wBruAus did not. Although wBruCon and wBruOri were easily eliminated by antibiotic treatments, wBruAus persisted over five treated generations and could not be eliminated. The inheritance pattern of wBruAus was, surprisingly, explained by sex-linked inheritance in male-heterozygotic organisms, which agreed with the karyotype ofC. chinensis(2n= 20, XY). Quantitative PCR analysis demonstrated that females contain around twice as muchwsptiter as males, which is concordant with an X chromosome linkage. Specific PCR and Southern blot analyses indicated that the wBruAus-bearing strain ofC. chinensiscontains only a fraction of theWolbachiagene repertoire. Several genome fragments of wBruAus were isolated using an inverse PCR technique. The fragments exhibited a bacterial genome structure containing a number of ORFs typical of the α-proteobacteria, although some of the ORFs contained disruptive mutations. In the flanking region offtsZgene, a non-long terminal repeat (non-LTR) retrotransposon sequence, which is typical of insects but not found from bacteria, was present. These results strongly suggest that wBruAus has no microbial entity but is a genome fragment ofWolbachiaendosymbiont transferred to the X chromosome of the host insect.

Kondo, N., Nikoh, N., Ijichi, N., Shimada, M., & Fukatsu, T. (2002). Genome fragment ofWolbachiaendosymbiont transferred to X chromosome of host insect. Proceedings of the National Academy of Sciences, 99(22), 14280–14285.