Ultrathin sections of high-pressure frozen cells of the Negativicutes member Megamonas rupellensis (A,C), and the Halanerobiales member Halanaerobium saccharolyticum (B,D). A Gram-negative like cell wall architecture is visible for both taxa (A,B): a cytoplasmic membrane (CM) surrounding the cytoplasm (C), a thin peptidoglycan layer (PG), and an outer membrane (OM). Pili-like structures (P) are also visible in M. rupelllensis. In some cases and due to a preparation artifact caused by swelling of the cells, the OM detaches from the IM creating an enlarged periplasmic space (PP) between two dividing cells (C,D). In these cases, the peptidoglycan becomes more apparent as it is also the case for an electron dense surface coat (SC), which might represent lipopolysaccharide (LPS) or a potential S-layer. Scale bars: 200 nm (A,C) and 100 nm (B,D).