Lipopolymers, Isoprenoids, and the Assembly of the Gram-Positive Cell Wall

Abstract

Several lines of evidence suggest that Gram-positive bacterial cell surface polymers are synthesized by stepwise addition of polymer subunits to an amphipathic acceptor. In the case of membrane-bound lipopolymers such as mannan and lipoteichoic acid, the finished product may be covalently linked to a lipid anchor. In the case of polymers that are transferred into preexisting cell wall, such as teichoic acid and peptidoglycan, two alternative fates might be possible: (1) transfer into wall with concomitant or later cleavage of the lipid anchor, with recycling of the lipid anchor or secretion of the lipid anchor into the growth medium, and (2) transfer into wall without cleavage of the lipid anchor, resulting in maintenance of the covalent relationship between lipid anchor and polymer chain. In the latter case, a close relationship should be established between the cell wall and the plasma membrane. A number of Gram-positive bacteria have been shown to be resistant to plasmolysis. Therefore, a model for the assembly of the Gram-positive cell wall is proposed which takes into account a role for lipopolymeric intermediates and which views the establishment of resistance to plasmolysis as the natural consequence of such a mechanism.