They are resistent to the proteinases tested and are not disintegrated by boiling in 2% sodium dodecylsulfate for 30 min. The sheaths consist of protein containing 18 amino acids and small amounts of neutral sugars. From cells of Methanospirillum hungatii no sacculi, but tube-like sheaths could be isolated, which tend to fracture perpendicularly to the long axis of the sheath along the fibrills seen on the surface. Therefore, the sacculi of the methanobacteria consist of a different polymer containing a set of three l-amino acids and one N-acetylated amino sugar. No muramic acid or d-amino acids typical of peptidoglycan were found. Neutral sugars and-in some strains-additional amounts of the amino sugars were present in variable amounts, and could be removed by formamide extraction or HF treatment without destroying the sacculi. ruminantium M 1) alanine is replaced by threonine, however. The sacculi of all the strains contained Lys: Ala: Glu: GlcNAc or GalNAc in a molar ratio of about 1:1.2:2:1. The ash content varied between 8 and 18% of dry weight.

Ultrathin sections of the isolated sacculi showed a homogenously electron dense layer of about 10–15 nm in width. Electron microscopy revealed the presence of sacculi exhibiting the shape of the original cells, on which no surface structure could be detected. Cell walls were prepared from freeze-dried samples of 7 strains of Methanobacterium by mechanical disintegration of the cells followed by incubation with trypsin.

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