Oligomerized backbone pilin helps piliated Lactococcus lactis to withstand shear flow

Mickaël Castelain,Marie-Pierre Duviau,Virginie Oxaran,Philippe Schmitz,Muriel Cocaign-Bousquet,Pascal Loubière,Jean-Christophe Piard,Muriel Mercier-Bonin

doi:10.1080/08927014.2016.1213817

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.

Highlights

Lactococcus lactis is a major lactic acid bacterium (LAB) present in numerous ecological niches involved in the global food chain (Cavanagh et al 2015)
This work confirms that pili are involved in the adhesion of L. lactis to solid surfaces under shear flow as suggested previously (Le et al 2013)
Pili from L. lactis consist of polymers of three pilins covalently linked together in a head-to-tail manner ie the major PilB pilin whose polymers form the pilus backbone, the accessory anchoring PilC pilin tethering the pilus to the cell wall and the accessory PilA cap pilin located at the distal end of the pilus

Summary

Introduction

Lactococcus lactis is a major lactic acid bacterium (LAB) present in numerous ecological niches involved in the global food chain (Cavanagh et al 2015). As LAB biota carry out crucial functions in the transformation of many agricultural products into processed food, the autochthonous LAB flora present in native products is often reinforced by the addition of bacterial starters usually consisting of cocktails of selected LAB in order to accelerate and better control fermentation processes. This practice leads to the presence of a large live LAB biota (~109 cfu g−1) that is ingested and delivered to the gastrointestinal tract (GIT) of humans and animals. Various uses have been proposed, including the delivery of antigens in live vaccine (Dieye et al 2003; Wells 2011), vitamins (LeBlanc et al 2005), enzymes (Li et al 2012), and immunomodulating effectors (Steidler et al 2000; Motta et al 2012)

Methods

Results

Conclusion