Isolated cell walls of Staphylococcus aureus and Micrococcus lysodeikticus were found to expand and contract in response to changes in environmental p H and ionic strength. These volume changes, which could amount to as much as a doubling of wall dextran-impermeable volume, were related to changes in electrostatic interactions among fixed, ionized groups in wall polymers, including peptidoglycans. S. aureus walls were structurally more compact in the hydrated state and had a higher maximum charge density than M. lysodeikticus walls. However, they were less responsive to changes in electrostatic interactions, apparently because of less mechanical compliance. In media of nearly neutral p H, S. aureus walls had a net positive charge whereas M. lysodeikticus walls had a net negative charge. These charge differences were reflected in Donnan distributions of mobile ions between wall phases and bulk medium phases. Cell walls of unfractionated cocci also could be made to swell and contract, and wall tonus in intact cells appeared to be set partly by electrostatic interactions and partly by mechanical tension in the elastic structures due to cell turgor pressure. The experimental results led to the conclusions that bacterial cell walls have many of the properties of polyelectrolyte gels and that peptidoglycans are flexible polymers. A reasonable mechanical model for peptidoglycan structure might be a sort of three-dimensional rope ladder with relatively rigid, polysaccharide rungs and relatively flexible polypeptide ropes. Thus, the peptidoglycan network surrounding cocci appeared to be predominantly an elastic restraining structure rather than a rigid shell.

Ou, L.-T., and R. E. MARQUIS. 1972. Coccal cell-wall compactness and the swelling action of denaturants. Can. J. Microbiol. 18: 623-629. Isolated cell walls of Micrococcla lysodeiktic~rs and Stap/tylococc~ts nrirel~s were found to have relatively low densities in both the dried and hydrated states. Thus, it appears that the component polymers of these structures do not form cr)stallites or other highly condensed assemblies, but rather, that their dislribution within the wall matrix is similar to that of the polymer chains in low-density, ion-exchange resins. Micrococclts lysodeikticlu walls, which are conlposed mainly of peptidoglycan, swelled significantly when they were heated or transferred to 8 M urea solution. This finding suggests that the compactness of walls and their component peptidoglycans is determined in part by weak interactions that can be disrupted by urea o r by heat.Ou, L.-T., et R. E. MARQUIS. 1972. Coccal cell-wall compactness and the swelling action of denaturants.Can. J. Microbiol. 18: 623-629. On a observt que les parois cellulaires isoltes de &Iicrococcris lysodeikticus et Stnp/rylococcus allreus ont de faibles densitts relatives, tant a l'etat sec qu'a l'ttat hydrate. I1 semble que les polymtres qui composent ces structures ne ferment pas de cristaux ou d'autres assemblages grandement condenses, mais que leur distribution dans la matrice de la paroi est semblable a celle des chafnes de polymires a faible densitC, i.e., les rtsines tchangeuses d'ions. Les parois de M . lysodeiktic~ts, lesquelles se composent principalement de peptidoglycans, renflent considtrable~nent lorsqu'elles sont chaufftes ou qu'elles sont transfertes dans une solution d'urte 8 M . Cette observation suggire que la cornpaticite des parois et de leur peptidoglycans est determinte en partie par des interactions faibles, ces derniires peuvent &tre rtduites par l'uree ou par la chaleur.

Cell walls isolated from a teichoic acid deficient mutant (52A5) of Staphylococcus aureus strain H were found to have lower capacities to bind cations than did walls of the parent strain. Both types of walls had higher binding affinities for Mg2+ and Ca2+ than for K+ and Na+. The reduced number of phosphate groups in 52A5 walls was reflected in a higher apparent pKa of 4.3 for displacement of Mg2+ (or Ca2+) during acid titration with HCl. The comparable pKa value for displacement of bound Mg2+ from parent-strain walls was 3.7. The reduced capacity of 52A5 walls to bind cations was not reflected in any significant increase in sensitivity to the growth inhibitory actions of ethylenediaminetetraacetate, low pH, or high NaCl concentrations. However, the 52A5 strain was somewhat more sensitive to the inhibitory effects of high pH. Also, mutant walls were found to be structurally more compact than walls of the parent strain, presumably because of less extensive electrostatic repulsion within the wall matrix.