Characterization of Helicobacter pylori lytic transglycosylases Slt and MltD

Peptidoglycan (PG) is a cell wall heteropolymer that is essential for cell integrity. PG hydrolases participate in correct assembly of the PG layer and have been shown to be required for cell division, cell daughter separation, and maintenance of bacterial morphology. In silico analysis of the Helicobacter pylori genome resulted in identification of three potential hydrolases, Sit, MltD, and AmiA. This study was aimed at determining the roles of the putative lytic transglycosylases, Sit and MltD, in H. pylori morphology, growth, and PG metabolism. Strain 26695 single mutants were constructed using a nonpolar kanamycin cassette. The sit and mltD mutants formed normal bacillary and coccoid bacteria in the exponential and stationary phases, respectively. The slt and mltD mutants had growth rates comparable to the growth rate of the parental strain. However, the mltD mutant exhibited enhanced survival in the stationary phase compared to the wild type or the slt mutant. PG was purified from exponentially growing bacteria and from bacteria in the stationary phase, and its muropeptide composition was analyzed by high-pressure liquid chromatography. This analysis revealed changes in the muropeptide composition indicating that MltD and Sit have lytic transglycosylase activities. Glycan strand analysis suggested that Sit and MltD have exo and endo types of lytic transglycosylase activity, indicating that Sit is involved mainly in PG turnover and MltD is involved mainly in rearrangement of the PG layer. In this study, we determined the distinct roles of the lytic transglycosylases Sit and MltD in PG metabolism.