A Multiscale Model of Fungal Impact on Chemotactic Behavior of Mycorrhizal Helper Bacteria

Abstract

Bacterial-fungal interactions play a fundamental role in many processes including crop biofuel development and biosystem design. in this talk, we focus on the interactions between the fungi Laccaria bicolor and the bacterium Psuedomonas fluorescens and their integral role in the fitness of the roots of the Populus tree. L. bicolor synthesizes trehalose which stimulates growth and chemotaxis of P. flourescens. Furthermore, P. flourescens provides L. bicolor with thiamine thereby increasing fungal mass. We developed a multiscale computational model to investigate these interdependent interactions. The growth and branching of the fungal mycelia are modeled using an off-lattice spatial discrete submodel which is dependent on both diffusive and metabolic translocation of internal nutrients and uptake of external nutrients. Trehalose secretion at the tips of the hyphae acts as a source of diffusive chemoattractant for P. fluorescens. The bacteria are modelled by subcellular elements submodel, a coarse-grained approach for describing biological properties of bacteria with great flexibility. Each bacterium is represented by multiple nodes connected to one another with linear and rotational springs and parameters calibrated using experimental measurements of mechanical properties of the bacteria. Bacterial motion is governed by potential functions and a propulsive force, calibrated using cell tracking data, which determine the movement and rearrangement of the nodes in an overdamped regime. We use simulations to evaluate the orientation and turning angle of the bacteria as they reverse their direction of motion in response to chemotactic signaling. The novelty of this multiscale model is that it takes into account: bacteria-bacteria, bacteria-external nutrient, and fungal-bacteria interactions and provides specific predictions to be tested in experiments. For example, we plan to test the impact of variations in fungal structures and nutrient excretion rates on bacterial chemotactic behavior.