Contribution of the Staphylococcus aureus Atl AM and GL Murein Hydrolase Activities in Cell Division, Autolysis, and Biofilm Formation

Abstract

The most prominent murein hydrolase of Staphylococcus aureus, AtlA, is a bifunctional enzyme that undergoes proteolytic cleavage to yield two catalytically active proteins, an amidase (AM) and a glucosaminidase (GL). Although the bifunctional nature of AtlA has long been recognized, most studies have focused on the combined functions of this protein in cell wall metabolism and biofilm development. In this study, we generated mutant derivatives of the clinical S. aureus isolate, UAMS-1, in which one or both of the AM and GL domains of AtlA have been deleted. Examination of these strains revealed that each mutant exhibited growth rates comparable to the parental strain, but showed clumping phenotypes and lysis profiles that were distinct from the parental strain and each other, suggesting distinct roles in cell wall metabolism. Given the known function of autolysis in the release of genomic DNA for use as a biofilm matrix molecule, we also tested the mutants in biofilm assays and found both AM and GL necessary for biofilm development. Furthermore, the use of enzymatically inactive point mutations revealed that both AM and GL must be catalytically active for S. aureus to form a biofilm. The results of this study provide insight into the relative contributions of AM and GL in S. aureus and demonstrate the contribution of Atl-mediated lysis in biofilm development.

Dual Targeting of Cell Wall Precursors by Teixobactin Leads to Cell Lysis

“…Murein hydrolase profiles were analyzed by zymogram (12,13). Antimicrobial agents at 10ϫ MIC were added to mid-exponential-phase JE2 cells in 15 ml Trypticase soy broth (TSB), and the cells were cultivated for an additional 4 h. Cultures were centrifuged and supernatants and cells were collected separately.…”

“…Teixobactin's bactericidal activity is dependent on Atl; hence, we decided to examine the lytic capacity of the supernatant of a culture treated with teixobactin. Atl undergoes maturation by proteolytic processing, resulting in generation of two extracellular lytic enzymes, an amidase and a glucosaminidase (12,14,23). If teixobactin treatment resulted in increased lytic enzyme production, we would expect the supernatant to have increased lysis capacity.…”

A Diagnostic Serum Antibody Test for Patients With Staphylococcus aureus Osteomyelitis

“…The secreted proteins each interfere with some element of the host immunity and collectively act to thwart the immune response [32]. In addition, some of these 14 proteins are reported to have important roles in building bacterial biofilms to establish chronic infections [4,6,18].…”

“…The sampling problem is compounded in chronic implant-associated infections owing to the formation of biofilms that sequester the bacteria. Newer approaches have been introduced to facilitate pathogen recovery in patient specimens including implant sonication [36], and PCR with harvested tissue or joint fluid [3,4]. To date, these methods are only modest improvements over conventional bacterial culture.…”

Various checkpoints prevent the synthesis ofStaphylococcus aureuspeptidoglycan hydrolase LytM in the stationary growth phase

“…7 Remodeling of the PG in S. aureus is in part achieved by different PG hydrolases (also known as autolysins) 8,9 whose functional redundancy may explain why individually, none of them are essential. [10][11][12] The PG hydrolases have also been associated with cell division and separation, protein secretion, biofilm formation [13][14][15][16][17][18][19] and with the bacterial programmed cell death (reviewed in 20 ). Within S. aureus, expression of the autolysins is repressed by the action of the 2-component systems ArlSR 21 and LytSR, 22 and the transcriptional regulator MgrA.…”