Adaptation of Escherichia coli Biofilm Growth, Morphology, and Mechanical Properties to Substrate Water Content

Abstract

Biofilms are complex living materials that form as bacteria become embedded in a matrix of self-produced protein and polysaccharide fibers. In addition to their traditional association with chronic infections or clogging of pipelines, biofilms currently gain interest as a potential source of functional material. On nutritive hydrogels, micron-sized Escherichia coli cells can build centimeter-large biofilms. During this process, bacterial proliferation, matrix production, and water uptake introduce mechanical stresses in the biofilm that are released through the formation of macroscopic delaminated buckles in the third dimension. To clarify how substrate water content could be used to tune biofilm material properties, we quantified E. coli biofilm growth, delamination dynamics, and rigidity as a function of water content of the nutritive substrates. Time-lapse microscopy and computational image analysis revealed that softer substrates with high water content promote biofilm spreading kinetics, while stiffer substrates with low water content promote biofilm delamination. The delaminated buckles observed on biofilm cross sections appeared more bent on substrates with high water content, while they tended to be more vertical on substrates with low water content. Both wet and dry biomass, accumulated over 4 days of culture, were larger in biofilms cultured on substrates with high water content, despite extra porosity within the matrix layer. Finally, microindentation analysis revealed that substrates with low water content supported the formation of stiffer biofilms. This study shows that E. coli biofilms respond to substrate water content, which might be used for tuning their material properties in view of further applications.

Curli amyloid fibers inEscherichia colibiofilms: the influence of water availability on their structure and functional properties

“…Such difference in structure could be explained by larger average spacings between strands (Figure 6), and the resulting flexibility of the curli fibers in the matrix could further contribute to the lower rigidity of biofilms grown on wet substrates. 8 The biofilms grown in the extreme conditions used in our experiments (0.5% and 2.5% agar) not only contained less curli, but this curli content also appeared to correlate with the rehydration capacity of the dried biofilms (Figure 1f-g). These results suggest that, in addition to providing biofilms with adhesion and rigidity, 3,8 curli fibers also promote biofilm water uptake from the surroundings.…”

“…For example, biofilms grown on substrates with a high water content spread more than biofilms grown on dryer substrates due to the lubricating effect of water ( Figure S1 ). 8 In this context, one could question if such confinement also affects the assembly of the curli fibers. Further studies will focus on clarifying if the water content of the substrate influences the molecular assembly of curli fibers in E. coli biofilms by affecting the nutrient transport or the confinement of the growth on the surface.…”

“…4,6 Indeed, biofilm morphogenesis is influenced by environmental cues such as the presence of salt, oxidative stress, charged surfaces and the water content substrate. 3,[6][7][8][9][10][11] These parameters may also determine biofilm properties via different mechanisms. For example, the flux of water driven by osmotic gradients induces biofilm swelling as well as nutrient transport, which in turn governs bacteria proliferation and matrix production.…”

Multispecies biofilm architecture determines bacterial exposure to phages

“…In V. cholerae, biofilm structure is characterized by tight cell packing coordinated by four matrix components: the proteins RbmA, RbmC, Bap1, and the polysaccharide VPS (46). E. coli biofilms, likewise, have been dissected extensively (48)(49)(50)(51)(52)(53). T7 phages are obligately lytic and routinely isolated from the environment alongside E. coli (54).…”

Influence of metal cations on the viscoelastic properties of Escherichia coli biofilms

“…For instance, substrate water content, temperature, pH and nutrients may be utilized as possible control parameters for tuning E. coli biofilm properties. 16,17 Another possible parameter is the addition of specific metal ions. Metal ions frequently bind to protein or carbohydrate structures in biological materials, 18 either forming mineralized composite materials [19][20][21][22] or sacrificial and selfhealing bonds.…”