Engineered Stochastic Adhesion Between Microbes as a Protection Mechanism Against Environmental Stress.

INTRODUCTION: Microbes aggregate when they display adhesive proteins on their outer membrane surfaces, which then form bridges between microbes. Aggregation protects the inner microbes from harsh environmental conditions such as high concentrations of antibiotics, high salt conditions, and fluctuations in pH. The protective effects of microbial aggregation make it an attractive target for improving the ability of probiotic strains to persist in the gut environment. However, it remains challenging to achieve synthetic microbial aggregation using natural adhesive proteins because these proteins frequently mediate microbial virulence.
OBJECTIVES: Construction of synthetic proteins that mediate aggregation between microbes to enhance the survival of cells delivered to stressful environments.
METHODS: We construct synthetic adhesins by fusing adhesive protein domains to surface display peptides. The resulting aggregated populations of bacteria are characterized using immunofluorescence, microscopy, flow cytometry, and quantification of colony forming units.
RESULTS: We assemble a series of synthetic adhesins, demonstrate their display on the outer membrane of Escherichia coli, and show that they mediate bacterial aggregation. Further engineering of the size and motif composition of the adhesive domain shows that principles from natural adhesins can be applied to our synthetic adhesins. Finally, we show that aggregation allows E. coli cells to resist treatment with antimicrobial peptides and survive inside the gut of Caenorhabditis elegans.
CONCLUSIONS: Our results demonstrate that synthetic aggregation can allow bacteria to resist biocidal environmental conditions. Synthetic adhesins may be used to facilitate microbial colonization of previously inaccessible environmental niches, either in remote natural environments or inside living organisms. © Biomedical Engineering Society 2018.