Collective motion of bacteria promotes soil water transport

Although rhizosphere microbiomes are known to enhance plants resistance to water stress, it is believed that only fungi actively contribute to the transport and uptake of water. We investigated the biomechanical impact of bacterial motility on water transport in soil by combining surface tension measurements and water infiltration experiments in soil microcosms. We observed that flagellar-based motility in the of the rhizobacteria Bacillus subtilis cells reduces the apparent surface tension of fluids by up to 15%. The effect reported depends on cell density and swimming speed, confirming its biomechanical origin, and was able to accelerate water infiltration and rewetting of soil. We conclude that Bacillus subtilis facilitates soil water transport through the deformation of air water interfaces in pores. SignificanceWater and light limitations to photosynthesis rarely occur simultaneously enabling plants in arid environments to allocate a greater proportion of assimilated carbon to belowground growth, particularly to rhizodeposition. Using microbial activity to convert chemical energy into mechanical work within soil pores offers a major opportunity for improving water use efficiency in agriculture, especially as farming shifts from polluting, energy-intensive mineral fertilisers toward resilient biological fertilisation alternatives.