Biosensors in complex environments such as the rhizosphere
Identifying types, and distributions, of nutrients found around plant roots is needed in order to better understand forces driving plant/microbe interactions.

Biosensor bacteria on roots

Tomato roots inoculated with bacteria that produce light when growing quickly. Colored areas indicate that conditions are capable of supporting rapid bacterial growth

However, nutrients near the root are difficult to study: they are hard to extract from soil, they are readily used by microorganisms and thus rapidly disappear, and it is difficult to sample the root region without disrupting nutrient distributions. We have overcome some of these problems by constructing and deploying bacterial reporters which fluoresce, or produce light via the Lux proteins, when particular nutrients are present in the root/soil environment. The reporters are simply inoculated into environmental chambers containing plants, and the root systems in the chambers are later observed by microscopy. The locations of fluorescing, or light emitting, bacteria indicate regions where particular nutrients are detected by the biosensing bacteria. Using this technology, nutrients and their locations in time and space can be observed around plant roots, and in soil. We are applying the technology to study how sugars, organic acids, bulk carbon and water potential support growth of bacteria around the roots of a variety plant species. Ultimately we hope to use these biosensors to investigate how carbon flow into the rhizosphere is modified in response to changes in plant physiology.This work is multidisciplinary and is being done in collaboration with Dr. Zoe Cardon at the Marine Biology Lab at Woods Hole, Dr. Leslie Shor, Dr. Yongku Cho and Dr. Jessica Furrer.