Physical confinement selectively favours bacterial growth based on cell shape

Abstract

AbstractHow are bacterial communities altered by changes in their microenvironment? Evidence from homogeneous liquid or flat plate cultures implicates biochemical cues — such as variation in nutrient composition1,2, response to chemoattractants and toxins3,4, and inter-species signalling5,6— as the primary modes of bacterial interaction with their microenvironment. However, these systems fail to capture the effect of physical confinement on bacteria in their natural habitats. Bacterial niches like the pores of soil, mucus, and infected tissues are disordered microenvironments with material properties defined by their internal pore sizes and shear moduli7–11. Here, using three-dimensional matrices that match the viscoelastic properties of gut mucus, we test how altering the physical properties of their microenvironment influences bacterial growth under confinement. We find that low aspect-ratio bacteria form compact, spherical colonies under confinement while high aspect-ratio bacteria push their progenies further outwards to create elongated colonies with a higher surface area, enabling increased access to nutrients. As a result, the population level growth of high aspect-ratio bacteria is more robust to increased physical confinement compared to that of low aspect-ratio bacteria. Thus, our results capture the first experimental evidence that physical constraints play a selective role in bacterial growth based on cell shape.