Using biosensors to understand how microbes interact with their environment

Abstract:

Rhizosphere processes such as nutrient cycling and greenhouse gas production are driven by microbes that coordinate collectively. This coordination is usually mediated through chemical communication via diffusible signaling molecules. Understanding how microbes will function as communities and respond to perturbations is crucial to predict the outcome of ecological processes in the future.

Engineered bacteria (biosensors) capable of sensing and reporting on specific environmental conditions of interest present us with a unique opportunity to studying microbial interactions in soils. In this work, we will describe two examples of how biosensors that detect different rhizosphere signals can provide mechanistic information about the modulation of microbial interactions by environmental properties.

First, we used a biosensor that responds to flavonoids, a secondary plant metabolite, to study how the bioavailable fraction varies with different soil amendments. We found that as plant-derived organic carbon accumulates on soil, it represses the flavonoid signal. The amount of repression is dependent on the chemical structure of the flavonoid and the availability of metal ions. This repression is sufficient to decrease legume nodulation.

Second, we used a biosensor that responds to acyl-homoserine lactones (AHL), a signal used to coordinate behaviors (e.g., biofilm formation, nitrogen fixation, and virulence) by gram-negative bacteria, to study how soil physicochemical properties affect this communication. We showed that soil pH and mineralogy impact the communication distance between two gram-negative bacteria.