H. J. Rogers

PEPTIDOGLYCANS (MUCOPEPTIDES): STRUCTURE, FUNCTION, AND VARIATIONS

Since the recognition of the unique composition of the cell walls of grampositive bacteria nearly two decades ago,’. a whole class of polymers has been found to be present in the outer covering of the Eubacteriales, the blue green algae, and at least some Chlamydiae. The only clear exceptions t o this generalization are the extreme halophiles. the Halobacteria. Rather than detailing the chemistry of individual peptidoglycans, an attempt will be made, after summarizing structural knowledge, to assess our prcscnt position with respect to the limits of variation and functions of these tough, resistant polymers. Mucopeptides are all built on the general patterns illustrated in FIGURE 1. They consist of glycan chains cross-linkcd together by short peptide chains that contain both D and L amino acids. They have received the dubious blessing of many christenings-two of the given names will be used indiscriminately in this article: “mucopeptide,” for historical precedence, and “pcptidoglycan,” which is clearly now becoming the name of popular choice.

Biogenesis of the Wall in Bacterial Morphogenesis

Publisher Summary The chapter discusses the biogenesis of the wall in bacterial morphogenesis. The characteristic shapes of bacterial cells can only be maintained by a contribution from all of the polymers in the walls, rather than by any one of them. Among the simplest and most easily defined changes in the shape of microorganisms is one from rods to spherical-shaped bacteria or from spherical protoplasts to rod-shaped bacilli. Several mutations and physiological conditions can bring about this change in different species of bacteria. Wall composition, biosynthetic mechanisms, and the physical properties of walls all refer to large populations of whole bacteria or broken preparations made from them. Changes in surface location of teichoic acids, or even more of the D-alanine substituent on it, within the wall of growing organisms could possibly have profound effects upon the morphology of the wall and upon cell shape. A complication of work with morphological mutants is the plethora of molecular and physiological changes that arise from single mutations. This difficulty can be overcome by finding two or more different sorts of mutations that have some of the biochemical changes in common, but which result in the same morphology.

The formation of extracellular enzymes by staphylococci.

This work was undertaken primarily to further our understanding of the mechanisms underlying the format ion of extracellular enzymes. Since, it still seems possible however, that some or all of the extracellular entities produced by staphylococci may be related to the ability of the organisms to harm the human host, it seems worth while to introduce, in this monograph, a few of the conclusions we have reached. The types of approach that should be kept in mind when reading this summary of the work which is still in progress, are as follows: if the various active substances, such as coagulase, a-, 0-, and y-hemolysin, leukocidin, and hyaluronidase, that have been described as occurring in filtrates from overnight broth cultures of staphylococci, are wholly extracellular, then the organism that gains access to the body, denuded of its growth medium, cannot usually rely upon their help to initiate infection. If, on the other hand, these active substances also remain associated with the cell as a kind of capsule, they are likely to be as important for initiating, as for maintaining or spreading the organisms from the site of entry. The speed a t which these various active substances are formed and accumulate may also be of importance to the invading parasite. A substance is clearly likely to be of most help to the attack on the host if it is formed faster than drainage from the area can remove it, or other defense mechanisms neutralize it. It is important to know the extent to which a strain can mutate to produce variants with different capacities to form the various aggressive agents. Also, attention has been paid to factors that can be recognized and estimated by these i n oilro effects on body constituents, but we have no idea as yet whether these factors constitute the whole or only a small fraction of the extracellular armory of the staphylococci. No complete answers to these problems are contained here, but some guiding indications may be found.