Abstract
BackgroundThe 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.ResultsAnalysis 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.ConclusionsThis 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 materialThe online version of this article (doi:10.1186/s12866-015-0347-2) contains supplementary material, which is available to authorized users.
Highlights
The bacterial cell surface is a crucial factor in cell-cell and cell-host interactions
In this study we investigated the impact of the EPS layer of L. johnsonii FI9785 on cell surface characteristics, biofilm formation and adhesion to tissues by making use of mutants where alterations in genes of an eps cluster had led to differences in phenotype, EPS quantity and EPS
We found that EPS production affected cell surface characteristics, cell-cell and cell-tissue interactions and the ability of the bacteria to resist stress
Summary
The bacterial cell surface is a crucial factor in cell-cell and cell-host interactions. 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. EpsC is a predicted tyrosine kinase and similar proteins in heteropolysaccharide biosynthetic gene clusters have been shown to be involved in EPS regulation, polymerisation and export [22,23]; the mutant epsCD88N had an increased accumulation of EPS consisting of both EPS-1 and EPS-2 [20,21] These strains were compared to a smooth colony mutant expressing the wild type epsC on a plasmid, again giving increased levels of EPS but having a wild type rough colony morphology. Our long term aim is to see whether the competitive exclusion potential can be improved by modulation of the EPS layer
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