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We have identified a new Bacillus subtilis gene, spoVT, whose gene product is homologous to the transcriptional regulator AbrB and serves as a regulator of E G

Bacterial cell envelope ultrastructure was investigated both by the progressive lowering of temperature embedding technique and freeze-substitution, using conventional and scanning transmission electron microscopy. Comparison with standard embedding procedures revealed a new aspect of cell envelope structure in specimens at low temperatures. The envelope was delimited by an electron-dark layer, beneath which was a uniform matter-containing layer lying between the outer and inner membranes. There was no empty periplasmic space. Buoyant densities of isolated peptidoglycan obtained in Percoll (1.02 to 1.07 g ml-') and CsC12 (1.44 g ml-') led to a calculated hydration of the peptidoglycan which was more than was previously assumed. Peptidoglycan therefore possibly finls the entire space between the inner and outer membranes in the form of a periplasmic gel. The new model of cell envelope organization is discussed with respect to the current knowledge on bacterial cell wall structure and function.

SUMMARY Studies using polar and non‐polar methacrylate‐based resins (Lowicryl® K4M and HM20) suitable for low temperature embedding are described. We present the first applications of the system to various membrane structures in glutaraldehyde‐fixed, uranyl acetate‐stained thin sections of bacteria, mitochondria and cell‐cell contact regions.

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