FIG. 7.

Schematic representation of the main conclusions of this paper. (A) In L. lactis MG1363 (and, for that matter, L. lactis NZ3900) AcmA hydrolyses peptidoglycan, resulting in cell lysis and subsequent protein release. AcmA is degraded by HtrA in the C-terminal domain which contains the LysM motifs (small black ovals). AcmA degradation results in a less active enzyme. (B) Since no AcmA is present in the acmA mutant of L. lactis MG1363, no lysis and protein release are observed for this strain. (C) In the dltD mutant of L. lactis, the reduction of d-alanylation of LTA results in a strong reduction of degradation of AcmA by HtrA. As a result, increased cellular lysis and protein release are observed. When AcmA is deleted in this dltD mutant, no lysis is observed (not shown in this figure, but compare with panel B). (D) An alr acmA double mutant, however, lyses, although AcmA is not present in this strain. The lysis of this strain is caused by an unknown factor. The high cellular lysis of the alr single mutant is most likely a combination of the reduced degradation of AcmA by HtrA, as shown in panel C and the AcmA-independent lysis as shown in panel D. A, AcmA; H, HtrA.