FIG. 2.

Electron microscopy analysis of G. obscuriglobus reveals a densely packed chromatin structure. (A and B) Transmission electron micrographs of G. obscuriglobus, high-pressure frozen and freeze-substituted (see Materials and Methods), exhibiting the condensed chromatin (white arrowheads). Typical G. obscuriglobus cell characteristics, i.e., the plasma membrane (PM), intracytoplasmic membrane (black arrowheads), peryphoplasm (P), riboplasm (R), and glycogen storage (white asterisk), are indicated. (C and D) Enlarged views of the regions framed white in panels A and B, respectively. The region framed in panel B is rotated 90° in panel D. The dense chromatin regions reveal a cholesteric, liquid crystal-like morphology. The double-membrane structure, separate between densely packed DNA regions, is evident (black asterisks). Scale bars, 500 nm (A and B) and 250 nm (C and D).