Role of HSL-Mediated Communication in Shaping Rhizosphere Community Function and Plant Health

Bacteria living around plant roots form complex microbial communities that can strongly influence plant growth, nutrient availability, and responses to environmental stress. Many Gram-negative bacteria communicate through small signaling molecules called homoserine lactones (HSLs), which allow cells to coordinate behaviors across a population or community. Although quorum sensing has been extensively studied in individual bacterial species, much less is known about how these signals are exchanged within multispecies rhizosphere communities and how this communication affects community function and plant health.

This project is part of a larger effort to understand and ultimately engineer communication within a synthetic community of bacteria associated with the rhizosphere of Sorghum bicolor. Rather than simply determining which HSL molecules are present, the project aims to connect bacterial signaling with changes in microbial gene expression, metabolism, community structure, nutrient cycling, and plant growth.

A major component of the undergraduate project will involve engineered bacterial biosensors that have been constructed to detect different HSL signals. The student will expose these biosensors to individual rhizosphere bacteria and synthetic microbial communities. Fluorescence responses will be quantified using flow cytometry and analyzed using FlowJo, Excel, and Python. By generating dose-response curves and comparing responses across different HSLs and bacterial samples, the student will evaluate properties such as sensor sensitivity, specificity, dynamic range, background activity, and signal cross-reactivity. Biosensor responses will also be compared with HSL profiles obtained using LC-MS/MS, providing an independent biological measurement that supports the chemical identification of signaling molecules and evaluates whether the sensors can be used to monitor communication in more complex microbial communities.

As the project progresses, the research will move from detecting bacterial communication to understanding its biological consequences. Transcriptomic approaches such as RNA-seq will be used to determine how exposure to different HSL signals changes gene expression within rhizosphere bacteria or synthetic communities. Metabolomic analyses will complement these experiments by examining changes in the small molecules produced by the community in response to HSL signaling. Together, these approaches can reveal which genes, pathways, and metabolic processes are controlled by interspecies communication and help explain how HSL signaling changes microbial community function.

Students who continue in the laboratory may become involved in the next stage of the project, in which communication itself is experimentally manipulated. Engineered rhizosphere bacteria capable of sensing or producing selected HSL signals will be introduced into synthetic microbial communities to control signaling between community members. The student may help investigate how altering these communication networks changes bacterial growth, community composition, and metabolic activity.

Longer-term students may also participate in plant-rhizosphere experiments using Sorghum bicolor. These experiments will involve growing sorghum plants under controlled conditions and inoculating the plants with defined synthetic bacterial communities containing natural or engineered HSL communication systems. Plants may be grown under different environmental conditions, including nitrogen limitation and drought, to determine whether changes in bacterial communication alter community behavior under stress. Measurements may include plant growth and biomass, microbial community dynamics, rhizosphere signaling, and processes related to nitrogen cycling and nitrogen mineralization. These experiments will help connect molecular-scale bacterial communication with community-level behavior and ultimately with plant performance.

By progressing from chemical identification of bacterial signals, to biosensor-based detection, to transcriptomic and metabolomic profiling, engineered microbial communication, and finally plant experiments, this project provides an opportunity to study a biological system across multiple scales. Ultimately, the research aims to determine whether microbial communication can be understood and manipulated to help design beneficial microbial communities that support plant growth and more sustainable agriculture.

The Andrews Lab has a strong track record of mentoring undergraduate researchers. We are a supportive and collaborative team. Students are expected to commit either 6 or 9 hours per week for research.Students who are interested to continue the project in additional years are especially encouraged to apply. Students who continue in future semesters can choose to pursue honors thesis research.