Characterisation of IsaA and SceD, two putative lytic transglycosylases of Staphylococcus aureus

Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom, Department of Microbiology and Genomics, School of Biological Sciences, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom, Dept. of Rheumatology and Inflammation Research, University of Göteborg, Guldhedsg 10, S-413 46 Göteborg, Sweden, Biosynexus Incorporated, 9119 Gaither Road, Gaithersburg, MD 20877, USA

^* To whom correspondence should be addressed. Email: s.foster{at}sheffield.ac.uk.

	Abstract

Bacterial cell wall peptidoglycan is a dynamic structure requiring hydrolysis to allow cell wall growth and division. Staphylococcus aureus has many known and putative peptidoglycan hydrolases, including two likely lytic transglycosylases. These two proteins, IsaA and SceD, were both found to have autolytic activity. Regulatory studies showed that isaA and sceD genes are partially mutually compensatory, with the production of SceD being upregulated in an isaA mutant. The expression of sceD is also greatly upregulated by the presence of NaCl. Several regulators of isaA and sceD expression were identified. Inactivation of sceD resulted in impaired cell separation, as seen by light microscopy, and "clumping" of bacterial cultures. An isaA sceD mutant is attenuated for virulence, whilst SceD is essential for nasal colonisation in cotton rats, thus demonstrating the importance of cell wall dynamics in host-pathogen interactions.