Study on the transport of the Opolysaccharide in Escherichia

点击翻译按钮获取中文摘要

O polysaccharides of Gram-negative bacteria are structurally polymorphic, and consequently, they are utilized as the O-antigen for serological typing. The O polysaccharide is part of lipopolysaccharides (LPS) and covalently binds to lipid A through the core-oligosaccharide portion. The wb* gene cluster is responsible for the O polysaccharide synthesis.The wb* cluster of Escherichia coll O9a strain F719 is constituted of eight genes, two for GDP-mannose synthesis, two for the putative ABC-transporter, three for mannosyltransferases, and one whose function is unknown. The gene, wbdD, was investigated its function using mutated plasmid and the complementation test. Tn1000 inserted plasmid synthesized the O9a polysaccharides but they did not transport to the cell surface instead found in cell cytoplasm. Electron microscopic analysis using a monoclonal antibody against the O9a polysaccharide confirmed this distribution of the polysaccharides. Cloned wbdD gene complemented the mutation, however, when the cloned gene was over expressed under the control of the lac promoter, the length of the O polysaccharides synthesized became shorter. Based on these results, the possibility was shown that there might be another transport system in addition to the ABC-transport system revealed by the genes in the cluster. Moreover, the change in the polysaccharide length suggested that the novel transport system might be correlated with the timing that the synthesized O polysaccharides are transferred to the core-oligosaccharide of LPS. More detailed analyzes would be necessary to confirm the hypothesis.