Thermo-responsive expression and differential secretion of the extracellular enzyme levansucrase in the plant pathogenic bacterium Pseudomonas syringae pv. glycinea

• Published in: FEMS microbiology letters Vol. 265; no. 2; pp. 178 - 185
• Main Authors: Li, Hongqiao, Schenk, Alexander, Srivastava, Abhishek, Zhurina, Daria, Ullrich, Matthias S.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2006; Blackwell; Oxford University Press
• Subjects: Amino acids; Bacteriology; Biogenesis of cell structures, supramolecular organization; Biological and medical sciences; Blotting, Northern; Blotting, Western; Exopolysaccharides; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation, Bacterial - physiology; Glycine max - microbiology; Hexosyltransferases - genetics; Hexosyltransferases - metabolism; Hot Temperature; Levan; Levansucrase; Low temperature; Microbiology; Molecular and cellular biology; Molecular genetics; Mutants; Pathogens; Periplasmic space; protein secretion; Proteins; Pseudomonas; Pseudomonas syringae; Pseudomonas syringae - enzymology; Pseudomonas syringae - genetics; Pseudomonas syringae - pathogenicity; Secretion; Temperature dependence; Temperature effects; Transcription; Virulence; Western blotting; Levansucrase; gene expression; protein secretion; Pseudomonadales; Plant pathogen; Enzyme; Secretion; Transferases; Glycosyltransferases; Gene expression; Protein; Pathogenicity; Pseudomonas syringae; Bacteria; Pseudomonadaceae; Hexosyltransferases; Molecular biology
• ISSN: 0378-1097; 1574-6968
• DOI: 10.1111/j.1574-6968.2006.00486.x

Abstract In the plant pathogen Pseudomonas syringae, production of the exopolysaccharide levan is mediated by extracellular levansucrase (Lsc), which is encoded by two functional genes, lscB and lscC. Comparison of extracellular protein profiles of P. syringae pv. glycinea PG4180 grown at 18 and 28°C and Western blots revealed that Lsc was predominantly found in the supernatant at 18°C, a temperature fostering virulence of this pathogen. Northern blot analysis indicated that transcription of lscB and lscC was temperature-dependent. Quantification of Lsc in supernatants and cellular protein samples of mutants defective in either lscB or lscC confirmed that LscB secretion at low temperature was due to a combination of thermo-regulated transcription and secretion. In contrast, LscC accumulated in the periplasmic space. LscB and LscC differ in only five amino acid residues, one of which is a cysteine residue. Temperature shift experiments suggested that de novo synthesized protein(s) at 18°C might be responsible for differential LscB secretion and that the presumed secretory machinery was stable when cells were shifted to 28°C. Our results imply that Lsc export and secretion may occur by yet-to-be identified novel mechanism(s).