Kageyama Daisuke, Anbutsu Hisashi, Watada Masayoshi, Hosokawa Takahiro, Shimada Masakazu, Fukatsu Takema
Graduate School of Arts and Sciences, University of Tokyo, Tokyo, Japan.
Appl Environ Microbiol. 2006 Oct;72(10):6667-73. doi: 10.1128/AEM.00803-06.
Male-killing phenotypes are found in a variety of insects and are often associated with maternally inherited endosymbiotic bacteria. In several species of Drosophila, male-killing endosymbionts of the genus Spiroplasma have been found at low frequencies (0.1 to 3%). In this study, spiroplasma infection without causing male-killing was shown to be prevalent (23 to 66%) in Japanese populations of Drosophila hydei. Molecular phylogenetic analyses showed that D. hydei was infected with a single strain of spiroplasma, which was closely related to male-killing spiroplasmas from other Drosophila species. Artificial-transfer experiments suggested that the spiroplasma genotype rather than the host genotype was responsible for the absence of the male-killing phenotype. Infection densities of the spiroplasma in the natural host, D. hydei, and in the artificial host, Drosophila melanogaster, were significantly lower than those of the male-killing spiroplasma NSRO, which was in accordance with the hypothesis that a threshold infection density is needed for the spiroplasma-induced male-killing expression.
雄性致死表型在多种昆虫中都有发现，并且通常与母系遗传的内共生细菌有关。在几种果蝇物种中，已发现低频率（0.1%至3%）的螺旋体属雄性致死内共生菌。在本研究中，未导致雄性致死的螺旋体感染在日本海德氏果蝇种群中很普遍（23%至66%）。分子系统发育分析表明，海德氏果蝇感染了单一菌株的螺旋体，该菌株与其他果蝇物种的雄性致死螺旋体密切相关。人工转移实验表明，螺旋体基因型而非宿主基因型导致了雄性致死表型的缺失。螺旋体在自然宿主海德氏果蝇和人工宿主黑腹果蝇中的感染密度显著低于雄性致死螺旋体NSRO的感染密度，这与螺旋体诱导雄性致死表达需要阈值感染密度的假设一致。
