Mechanisms of Early Microbial Establishment on Growing Root Surfaces

Core Ideas Models for bacterial colonization of root tips require root growth kinematics. Rates of root elongation and bacterial attachment affect exposure to root exudates. Microbial attachment to roots contributes to dispersion of microbes in soil. The root cap may play a role in the maintenance of bacteria at the tip. Microbial activity in the soil surrounding plant roots contributes to nutrient bioavailability, crop growth, and soil biodiversity and fertility. Colonization of the rhizosphere and the rhizoplane in particular requires early establishment on root surfaces where sources of nutrients are abundant. In this study, we investigated the physical interactions taking place between bacteria and the root surface when a root tip enters unexplored regions of soil. We developed a theoretical framework that generalizes the prevailing approaches for describing root growth kinematics and bacterial growth and adhesion on root surfaces. We found that the root elongation rate, bacterial attachment rate, and root cap carrying capacity are key traits for successful establishment. Models also indicate that chemotaxis is more important for radial transport and adhesion than for longitudinal movement of bacteria. Controls on bacterial attachment are required for both efficient root colonization and subsequent dispersal of bacteria in soil. The findings of this study help to understand the establishment of the structure and composition of microbial communities in soil.