Transcriptional analysis and secretion of levansucrases from Pseudomonas syringae
Three alleles encoding for levansucrase (Lsc) from the plant pathogen, Pseudomonas syringae, had previously been identified, from which two were actively expressed. Promoter mapping, determination of the transcriptional start site, and analysis of the secretion of Lsc are in the focus of this project. Lsc (E.C.2.4.1.10) synthesizes a high-molecular weight biopolymer, levan, which is a β-(2,6) polyfructan with extensive branching through β-(2,1) linkages. In certain bacterial strains, Lsc has been shown to be synthesized thermo-responsively, i.e. at 18°C its synthesis is maximal, while in others Lsc is produced maximally at the optimal growth temperature, i.e. 28°C. Interestingly, the two expressed Lsc differ in only a few amino acyl residues. However, their secretion patterns differ remarkably: One Lsc (LscB) is secreted to the exterior while the other, LscC, remains in the periplasmic space after export through the inner membrane. The enzymatic characteristics of LscB are investigated in detail.
Atomic force micrograph of Pseudomonas syringae cells producing the exopolysaccharide levan.