The role of a new S. aureus hydrolase in Peptidoglycan degradation

Staphylococcus aureus is one of the most common human microbial pathogens, responsible for several diseases such as pneumonia and sepsis. Infections caused for this microorganism have become progressively harder to treat due to the arising of antibiotic resistance observed in clinical strains. Staphylococcus aureus are Gram-positive bacteria. Its cell wall is characterized by a thick peptidoglycan layer that is important to bacteria as defects in its maintenance (degradation and synthesis) compromise the cell wall structure and result in bacteria death. Proteins responsible for Peptidoglycan (PGN) degradation, the major cell wall element, are called autolysins (or PGN hydrolases). Atl is the major S. aureus autolysin and is responsible for daughter cell separation in cellular division. Sle1 is another known peptidoglycan hydrolase produced by S. aureus that, together with Atl, is involved in the cell separation of S. aureus bacteria, as the double mutant presents an increased number of irregular clusters of bacteria. In this work, I have studied another S. aureus NCTC 8325 PGN hydrolase, which is encoded by saouhsc_00773, that has a peptide sequence similar to that of Sle1. From this gene, a 29kDa protein was expressed and successfully isolated. This protein presented PGN hydrolytic activity in Zymography and also in direct incubation with purified PGN. However, the S. aureus mutant strain that lacks this gene, which was also produced during the framework of this project, did not present observable differences in growth rate relatively to the parental S. aureus strain