Life in a tight spot: Coupled dynamics of bacteria and soil across scales

Soil harbors much of Earth’s bacterial life. The activity of these bacteria governs plant growth, carbon and nitrogen cycling, and the response of land to a changing climate. Understanding this activity is difficult, however: soil is structurally and chemically heterogeneous and optically opaque, and its bacteria not only respond to their surroundings but continually reshape them, a two-way feedback that most idealized experiments and theories overlook. Here we review how this dynamic feedback governs the physics of bacterial motility, growth, and sensing in soil across three scales – the single pore, the mesoscale of many pores, and the broader landscape.