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. 2015 Feb 4;15(1):8.
doi: 10.1186/s12866-015-0347-2.

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

Enes Dertli  1   2 , Melinda J Mayer  3 , Arjan Narbad  4
Affiliations

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

Enes Dertli et al. BMC Microbiol. .

Abstract

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.

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Figures

Figure 1
Figure 1
Physiochemical characteristics of L. johnsonii FI9785 and mutant strains. (A) Zeta potential as a function of pH (black, pH 3, light grey, pH 7, dark grey, pH 10) in a 10 mM phosphate buffer, (B) Percentage adhesion to hexadecane. Error bars represent standard deviations of triplicates (A, B) for each strain; *, p < 0.05, **, p < 0.01.
Figure 2
Figure 2
Influence of EPS on biofilm formation. A crystal violet staining assay was conducted for wild type and mutants grown with sucrose (dark grey) or glucose (light grey). Results are the mean of triplicate experiments with six replicates per experiment +/− standard deviation; *, p < 0.05, **, p < 0.01.
Figure 3
Figure 3
Effect of alterations in EPS on aggregation profiles of L. johnsonii FI9785. (A) the aggregation percentage of wild type and mutant strains after overnight incubation (16 h) analysed by FCM, *, p < 0.05, **, p < 0.01; (B) OD600 measurements of L. johnsonii FI9785 (▲), epsC D88N (■), epsC D88N ::pepsC (□), ΔepsE (●), ΔepsE::pepsES (○) and ΔepsE::pepsEA/S (♦) over an 8 h time period at room temperature.
Figure 4
Figure 4
Adhesion of L. johnsonii strains to chicken gut explants. The error bars represent standard deviations of triplicate samples for each strain; *, p = 0.05.
Figure 5
Figure 5
Protective effect of EPS on resistance to antimicrobials, heat and acid shock. The wild type (▲), epsC D88N (■) or ΔepsE (●) strains were grown in the presence of 2 μg ml−1 ampicillin (A), 1 μg ml−1 tetracycline (B), 0.25 μg ml−1 nisin (C) or 0.3% bile salts (D) or were exposed to 60°C (light grey) or 50°C (dark grey) for 5 min or pH 2 (black) for 90 min (E); bars represent percentage survival, *, p < 0.05.
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