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Background  The bacterial cell surface is a crucial factor in cell-cell and cell-host interactions.  Lactobacillus johnsonii  FI9785 produces an exopolysaccharide (EPS) layer whose quantity and composition is altered in mutants that harbour genetic changes in their  eps  gene clusters. We have assessed the effect of changes in EPS production on cell surface characteristics that may affect the ability of  L. johnsonii  to colonise the poultry host and exclude pathogens.    Results  Analysis of physicochemical cell surface characteristics reflected by Zeta potential and adhesion to hexadecane showed that an increase in EPS gave a less negative, more hydrophilic surface and reduced autoaggregation. Autoaggregation was significantly higher in mutants that have reduced EPS, indicating that EPS can mask surface structures responsible for cell-cell interactions. EPS also affected biofilm formation, but here the quantity of EPS produced was not the only determinant. A reduction in EPS production increased bacterial adhesion to chicken gut explants, but made the bacteria less able to survive some stresses.    Conclusions  This study showed that manipulation of EPS production in  L. johnsonii  FI9785 can affect properties which may improve its performance as a competitive exclusion agent, but that positive changes in adhesion may be compromised by a reduction in the ability to survive stress.    Electronic supplementary material  The online version of this article (doi:10.1186/s12866-015-0347-2) contains supplementary material, which is available to authorized users.

Impact of the exopolysaccharide layer on biofilms, adhesion and resistance to stress in Lactobacillus johnsonii FI9785