Turnover of cell walls in microorganisms

Abstract

Cell wall is produced by cells at the expense of considerable energy. Turnover of cell wall may therefore seem to be a costly process, especially if the cell is unable to recycle the turned-over material. So turnover must be considered as part of the overall strategy of growth of the cell. The tension created in the wall by the uptake of nutrients and the biosynthesis of new metabolites must be compensated for by surface expansion. Excision of preexisting wall allows for surface expansion and exposes sites at which new wall materials can be added. Turnover does not necessarily create new acceptor sites for nascent peptidoglycan oligomers, but it can. Newly synthesized peptidoglycan is inserted on the inner wall face near the plasma membrane. When the peptidoglycan becomes cross-linked it assumes tension created by the turgor pressure of the cell. Incorporation of newer peptidoglycan pushes older wall father from the plasma membrane. When the peptidoglycan has been pushed to near the wall exterior, it is highly stressed and may be cleaved by autolysins, causing turnover. The clipping of the most highly stressed peptidoglycan by autolysins partially alleviates tension in the wall and allows for surface expansion. So cell growth and wall turnover are tightly coupled in many bacteria. For many microorganisms, turnover is an essential part of cell growth. In this review, surface stress is emphasized as a driving force for cell wall turnover in procaryotes and eucaryotes.