MICROBIAL CELL WALLS 



developing wall of Phycomyces blakesleeanus sporangio- 

 phores were 150 to 250 A thick. The average fibril direction 

 was too uncertain to suggest a spiral structure, but the inner 

 layer showed a roughly transverse orientation. Thin sections 

 of Neurospora crassa prepared by Shatkin and Tatum ^~ 

 showed a wall containing fine fibrils in a homogeneous 

 matrix. The wall structure is much more readily shown in 

 isolated mycelial fragments prepared by disintegration of 

 Neurospora crassa by the methods used for bacterial cell- 

 wall isolation. Figure 2>a illustrates the appearance of an 

 isolated mycelial wall with a rough outer texture and the 

 more detailed microfibrillar structure of the wall in Fig. 36 

 (Chapman and Salton ^^). 



No such fibrillar layer has been detected in the walls of 

 bacteria, although the walls of Bacillus megaterium give a 

 vague impression of being fibrous (Fig. 4). The walls of 

 many Gram-positive bacteria, such as those of Staphylococ- 

 cus aureus and Streptococcus faecalis, have a homogeneous 

 appearance, and only thickened bands at what is presumed 

 to be the site of new wall formation can be seen. 



A type of fine structure differing from that observed in 

 yeast walls and various algae 2^- ^^ was first reported by 

 Houwink ^^ on examination of the wall of a large Spirillum 

 species. The cell wall of this organism was a multilayered 

 structure, with one layer composed of spherical macromole- 

 cules*^ packed hexagonally. Such a macromolecular layer 

 was also observed in the wall of Spirillum serpens, and 

 Salton and Williams ^^ found a similar type of fine structure 

 in the wall of Rhodospirillum rubrum. This spherical 

 macromolecular type of structure is apparently not uncom- 

 mon, for Houwink ^^ detected it also in the wall of Halobac- 

 terium halobium. Figure 5 illustrates the hexagonally 

 packed macromolecular fine structure found in the wall of 

 Halobacterium halobium. 



