Figure 3.

Monitoring cell-cell communication in environmental materials. (A) AHL cell-cell signaling (middle) regulates processes at the cm-scale that contribute to fluxes at a planetary scale, including: (left) the production of enzymes that degrade marine sinking particulate organic carbon, and (right) the transfer of symbiotic plasmids encoding nitrogen-fixing machinery and the production of nitrous oxide. Analytical chemistry methods for monitoring signals can present: (B) high limits of quantification (LOQ) that preclude signal detection, (C) an overestimation of signal levels, since spatial variability and bioavailability are not reflected in bulk extraction data, and (D) limited temporal insight because samples are consumed during analysis. (E) Biosensors can provide a microbe's perspective on the bioavailability of a signal at the micron scale, which varies due to consumption, enzymatic modification, abiotic chemical modification, sorption into the organo-mineral phase, and spatial accessibility. (F) Multiple biosensors are needed to understand the complex signaling that underlies plant-microbe symbiosis whose formation is critical to crop productivity. Biosensors are needed to understand how soil properties, signal chemistry, and amendments affect: (1) microbial growth, (2) microbe-microbe AHL signaling that underlies symbiotic plasmid transfer, and (3) plant-microbe communication mediated by flavonoids and nodulation factors that cause symbiosis formation.