Beyond growth: novel functions for bacterial cell wall hydrolases

Abstract

The peptidoglycan cell wall maintains turgor pressure and cell shape of most bacteria. Cell wall hydrolases are essential, together with synthases, for growth and daughter cell separation. Recent work in diverse organisms has uncovered new cell wall hydrolases that act autonomously or on neighboring cells to modulate invasion of prey cells, cell shape, innate immune detection, intercellular communication, and competitor lysis. The hydrolases involved in these processes catalyze the cleavage of bonds throughout the sugar and peptide moities of peptidoglycan. Phenotypes associated with these diverse hydrolases reveal new functions of the bacterial cell wall beyond growth and division.

Figure 1

Cleavage specificities of PG hydrolases described in this review. PG hydrolase class is color coded as indicated in the key. With the exception of AmiA, cleavage specificity is supported by biochemical data as cited in the main text.

Figure 2

Observed functions of representative PG hydrolases described in this review. Rows (a)–(c) depict a steady-state shape phenotype during logarithmic growth in deletion mutants (left), wild-type (middle), and overexpression strains (right). Rows (d)–(f) depict dynamic processes resulting from hydrolase activity. The middle shows the starting state. Cells to the right demonstrate wild-type behavior, while cells to the left depict the same behavior for the indicated hydrolase deletion mutant. Color coding of hydrolases is the same as in Figure 1.