Curli fibers in Escherichia coli biofilms: the influence of water availability on amyloid structure and properties

E. coli biofilms consist of bacteria embedded in a self-produced matrix mainly made of protein fibers and polysaccharides. The curli amyloid fibers found in the biofilm matrix are promising versatile building blocks to design sustainable bio-sourced materials. To exploit this potential, it is crucial to understand i) how environmental cues during biofilm growth influence the molecular structure of these amyloid fibers, and ii) how this translates at higher length scales. To explore these questions, we studied the effect of water availability during biofilm growth on the conformation and functions of curli. We used microscopy and spectroscopy to characterize the amyloid fibers purified from biofilms grown on nutritive substrates with different water contents, and micro-indentation to measure the rigidity of the respective biofilms. The purified curli amyloid fibers present differences in the yield, structure and functional properties upon biofilm growth conditions. Fiber packing and {beta}-sheets content correlate with their hydrophobicity and chemical stability, and with the rigidity of the biofilms. Our study highlights how E. coli biofilm growth conditions impact curli structure and functions contributing to macroscopic materials properties. These fundamental findings infer an alternative strategy to tune curli structure, which will ultimately benefit to engineer hierarchical and functional curli-based materials. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=169 SRC="FIGDIR/small/517345v3_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@124ddd2org.highwire.dtl.DTLVardef@15f234dorg.highwire.dtl.DTLVardef@106a65forg.highwire.dtl.DTLVardef@194c53f_HPS_FORMAT_FIGEXP M_FIG C_FIG