Oligomerized backbone pilin helps piliated Lactococcus lactis to withstand shear flow

Abstract

The present work focuses on the role of pili present at the cell surface of Lactococcus lactis in bacterial adhesion to abiotic (hydrophobic polystyrene) and biotic (mucin-coated polystyrene) surfaces. Native pili-displaying strains and isogenic derivatives in which pilins or sortase C structural genes had been modified were used. Surface physico-chemistry, morphology and shear-flow-induced detachment of lactococcal cells were evaluated. The involvement of pili in L. lactis adhesion was clearly demonstrated, irrespective of the surface characteristics (hydrophobic/hydrophilic, presence or not of specific binding sites). The accessory pilin, PilC, and the backbone pilin, PilB, were revealed to play a major role in adhesion, provided that the PilB was present in its polymerized form. Within the population fraction that remained attached to the surface under increasing shear flow, different association behaviors were observed, showing that pili could serve as anchoring sites thus hampering the effect of shear flow on cell orientation and detachment.

Keywords:

• Adhesion
• pili
• shear flow
• Lactococcus lactis

Acknowledgements

The authors are grateful to Christophe Ellero and Nathalie Clergerie for their technical assistance in image processing and electrophoretic mobility experiments. They thank the Research Federation FERMaT (Toulouse, France) for providing access to the Morphologi device, and Luc Fillaudeau for technical assistance and helpful discussions. Finally, they are grateful to Isabelle André for fruitful discussion about the HCA predicting tool.