The Structure and Function of the Spore Outer Membrane in Dormant and Germinating Spores of Bacillus megaterium

Attempts to demonstrate the presence of the spore outer membrane in mature, dormant spores of a strain of Bacillus megaterium are described. The outer, integument, layers of this organism were found to contain one-third of the total spore cytochrome content, several enzymes of the electron transport chain (specifically NADH oxidase, dehydrogenase, cytochrome c reductase and NADPH dehydrogenase) and a large number of polypeptides extractable with sodium dodecylsulphate in the presence of dithiothreitol and protease inhibitors. These all suggest the presence of a membraneous element. Electron microscopic evidence is presented on the structure of the dormant integument enzymes. Changes in the integument enzymes and in the gel electrophoresis profile of the extractable integument polypeptides which occur during spore gemination, are described and compared with those that take place in the spore inner membrane. The heat sensitivity of the integument enzymes is compared with that of the inner membrane enzymes and the implications for theories of spore heat resistance discussed.