FIG. 1.

Micrographs of Epulopiscium-like symbionts of N. lituratus. Collection times are provided in the upper left of each set of images. (A and B) Phase-contrast (PC) images of surgeonfish intestinal contents. In these panels, representatives of the C and J morphotypes are indicated with arrows. Note the prominent phase-bright intracellular offspring seen in the midnight (00:00) sample only. (C to H) Higher magnification images of individual type C (C and D) or J (E to H) cells. The type of image is indicated above each column: DAPI, fluorescence; DIC, Nomarski differential interference contrast. For some, PC images are also provided. PC images were taken with short exposure times to prevent saturation of pixels and to preserve cell structure. (C) Bright DNA staining within the cytoplasm of two large, phase-dark forespores. (D) DAPI cannot penetrate the phase-bright spores but instead associates with the outer most layers of these offspring. (E to H) Developmental progression of a type J endospore. Each panel focuses on the tip of a type J cell. Drawings are provided in the DIC panels for E and G to illustrate the position of the forespore within a mother cell. (E) Bright DAPI staining within the cytoplasm of a forespore. (F) The forespore DNA takes on a rope-like configuration (upper cell). A mature endospore (lower cell in this series) shows smooth, peripheral staining with DAPI. (G) PC and DIC show an offspring with a slightly rough or irregular surface appearance. DAPI can enter the cytoplasm of this forespore and stain the DNA. (H) A mature endospore is phase-bright and has a smooth outer surface in DIC and PC optics. DAPI cannot enter the core of the mature spore but instead staining of the cortex is observed. Scale bars represent 20 μm. Scale bar in A also applies to B. The scale in D applies to C also. The bar in H applies to panels E to H.