Proteins exported via the PrsD-PrsE type I secretion system and the acidic exopolysaccharide are involved in biofilm formation by Rhizobium leguminosarum.
The type I protein secretion system of Rhizobium leguminosarum bv. viciae encoded by the prsD and prsE genes is responsible for secretion of the exopolysaccharide (EPS)-glycanases PlyA and PlyB. The formation of a ring of biofilm on the surface of the glass in shaken cultures by both the prsD and prsE secretion mutants was greatly affected. Confocal laser scanning microscopy analysis of green-fluorescent-protein-labeled bacteria showed that during growth in minimal medium, R. leguminosarum wild type developed microcolonies, which progress to a characteristic three-dimensional biofilm structure. However, the prsD and prsE secretion mutants were able to form only an immature biofilm structure. A mutant disrupted in the EPS-glycanase plyB gene showed altered timing of biofilm formation, and its structure was atypical. A mutation in an essential gene for EPS synthesis (pssA) or deletion of several other pss genes involved in EPS synthesis completely abolished the ability of R. leguminosarum to develop a biofilm. Extracellular complementation studies of mixed bacterial cultures confirmed the role of the EPS and the modulation of the biofilm structure by the PrsD-PrsE secreted proteins. Protein analysis identified several additional proteins secreted by the PrsD-PrsE secretion system, and N-terminal sequencing revealed peptides homologous to the N termini of proteins from the Rap family (Rhizobium adhering proteins), which could have roles in cellular adhesion in R. leguminosarum. We propose a model for R. leguminosarum in which synthesis of the EPS leads the formation of a biofilm and several PrsD-PrsE secreted proteins are involved in different aspects of biofilm maturation, such as modulation of the EPS length or mediating attachment between bacteria.
Russo
Daniela M
DM
Fundación Instituto Leloir, CONICET, and Inst. de Investigaciones Bioquímicas, FCEyN, University of Buenos Aires, Patricias Argentinas 435, (C1405BWE) Buenos Aires, Argentina.
Williams
Alan
A
Edwards
Anne
A
Posadas
Diana M
DM
Finnie
Christine
C
Dankert
Marcelo
M
Downie
J Allan
JA
Zorreguieta
Angeles
A
D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000143:Acids; D001426:Bacterial Proteins / Q000378:metabolism* / Q000502:physiology; D018441:Biofilms / Q000254:growth & development*; D006026:Glycoside Hydrolases; D011135:Polysaccharides, Bacterial / Q000378:metabolism / Q000502:physiology*; D016961:Rhizobium leguminosarum / Q000502:physiology*
D018528:ATP-Binding Cassette Transporters; D000143:Acids; D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial; C106236:PrsD protein, Rhizobium leguminosarum; C106237:PrsE protein, Rhizobium leguminosarum; D006026:Glycoside Hydrolases; C020668:glycanase