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Appl Environ Microbiol. 1975 June; 29(6): 841-849
Copyright © 1975 American Society for Microbiology. All Rights Reserved.

Ultrastructure of Cell Envelopes of Bacteria of the Bovine Rumen

Research Station, Agriculture Canada, Lethbridge, Alberta, Canada T1J 4B1, and Department of Biology, University of Calgary, Calgary, Alberta, Canada T2N 1N4

ABSTRACT

Most of the bacteria found in rumen fluid samples taken from cows fed hay, or a concentrate diet, had cell walls of the gram-negative type. Most were intact, with only a small proportion of lysed cells, and many of the cells contained electron-translucent cytoplasmic deposits similar to the carbohydrate reserve material described in pure cultures of rumen organisms. All of the bacteria observed in these samples had an external "coat" layer outside the outer membrane when fixed in glutaraldehyde and osmium, stained with uranyl acetate and lead citrate, and examined as sectioned material. These coat layers varied from thin (ca. 8 nm) structures to very extensive fibrous systems, sometimes including concentric arrangements and radial fibers extending up to 1,200 nm from the cell. The thin-coat layers sometimes exhibited a rough periodicity. In all, 10 different types of coat layers were distinguished on a morphological basis. It is proposed that these external coat layers have protective and adherence functions for the rumen bacteria in the environment.