Abstract
Internal epithelial surfaces in humans are both oxygenated and physically protected by a few hundred microns thick hydrogel mucosal layer, conditions that might support bacterial aerotaxis. However, the potential role of aerotaxis in crossing such a thin hydrogel layer is not clear. Here, we used a new setup to study the potential role of motility and chemotaxis in the bacterial colonization of surfaces covered by a thin hydrogel layer and subjected to a vertical oxygen gradient. Using the bacterium Escherichia coli, we show that both non-motile and motile-but-non-chemotactic bacteria could barely reach the surface. However, an acquired mutation in the non-chemotactic bacteria that altered their inherent swimming behavior led to a critical enhancement of surface colonization. Most chemotactic strains accumulated within the bulk of the hydrogel layer, except for the MG1655 strain, which showed a unique tendency to accumulate directly at the oxygenated surface and thus exhibited distinctly enhanced colonization. Even after a long period of bacterial growth, non-motile bacteria could not colonize the hydrogel. Thus, switching motility, which can be spontaneously acquired or altered in vivo, is critical for the colonization of such protected surfaces, whereas aerotaxis capacity clearly expedites surface colonization, and can lead to diverse colonization patterns.
Highlights
Glass Gel 0.4% Non-motile if one or more flagella switch to the opposite direction, that flagellum leaves the bundle, and the cell switches its swimming direction
Similar to all motile bacteria, E. coli is equipped with a sensory system that detects external chemical changes along the bacterial swimming trajectory and guides the bacterium along chemical gradients, a behavior known as chemotaxis[23]
We report a new chemotaxis setup used to study the contribution of bacterial motility and chemotaxis to the ability of bacterial cells to colonize surfaces protected by a thin hydrogel layer subjected to a vertical oxygen gradient across the layer
Summary
Glass Gel 0.4% Non-motile if one or more flagella switch to the opposite direction (clockwise, CW), that flagellum leaves the bundle, and the cell switches its swimming direction. Similar to all motile bacteria, E. coli is equipped with a sensory system that detects external chemical changes along the bacterial swimming trajectory and guides the bacterium along chemical gradients, a behavior known as chemotaxis[23]. This sensory system consists of four types of MCP chemoreceptors with various sensing specificities and an additional MCP-like Aer receptor[24]. We tested the capacity of different E. coli strains, including strains with specific motility or chemotaxis properties, to populate the hydrogel layer and colonize the surface
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