Confocal micrographs (optical sections) showing dynamics of <i>Carsonella</i> and <i>Profftella</i> during the embryogenesis of <i>D</i>. <i>citri</i>.

<p>Whole-mount FISH images of embryos. Red (Alexa Fluor 594), green (Alexa Fluor 488), and blue (DAPI) signals indicate <i>Carsonella</i>, <i>Profftella</i>, and the host nuclei, respectively. (A) Blastula-stage embryo collected at 0–6 h post-oviposition. A tightly aggregated ball-like mosaic mass of <i>Carsonella</i> and <i>Profftella</i> can be observed at the posterior pole of the embryo. (B) An embryo at 6–12 h post-oviposition. The symbiont mass was loosening. (C) An embryo at 12–18 h post-oviposition. <i>Carsonella</i> and <i>Profftella</i> can be observed in the central and peripheral parts of the mass, respectively. Host nuclei are observed in the symbiont mass. (D) An embryo18–24 h post-oviposition. <i>Carsonella</i> and <i>Profftella</i> can be observed in the central syncytium and peripheral uninucleate bacteriocytes, respectively. (E) An embryo at 24–30 h post-oviposition. The head of the germ band nears the proto-bacteriome. Uninucleate bacteriocytes harboring <i>Profftella</i> migrate toward the posterior pole. (F) A katatrepsis-stage embryo at 30–36 h post-oviposition. The uninucleate bacteriocytes harboring <i>Profftella</i> assemble at the posterior pole, whereas the syncytium containing <i>Carsonella</i> resides on the anterior side of the mass. (G) An embryo (36–48 h post-oviposition) in the process of dorsal closure. The syncytium harboring <i>Carsonella</i> is divided into uninuclear bacteriocytes and begins to surround the mass of <i>Profftella</i>-containing bacteriocytes. (H) An embryo at 48–60 h post-oviposition. The proto-bacteriome is settled within the embryo. (I) An embryo at 60–72 h post-oviposition. The mass of bacteriocytes harboring <i>Profftella</i> is fused into a syncytium, which is completely surrounded by uninuclear bacteriocytes containing <i>Carsonella</i>. (J) An embryo at 72–84 h post-oviposition. Two wing-like protrusions start to grow from the lateral sides of the bacteriome. (K) Enlarged image of the symbiont mass with host nuclei shown in C. (L) Enlarged image of the cellularized proto-bacteriome shown in D. (M) Enlarged image of the proto-bacteriome shown in H. <i>Profftella</i>-containing bacteriocytes are still uninucleate. (N) Enlarged image of the proto-bacteriome shown in I. <i>Profftella</i>-containing bacteriocytes are fused into a syncytium. Abbreviations: a, abdomen; gb, germ band; h, head; t, thorax; y, yolk. Scale bars: 50 μm for A–J, 10 μm for K–N. Arrows indicate the presumed direction of motion of the embryo.