Charcoal enters soil naturally following fires. Charcoal soil amendment is also used to sequester carbon, improve fertility, and remediate environmental contaminants owing to its unique physicochemical properties. However, charcoal can also trigger a range of undesired detrimental effects upon soil amendment, such as increasing nitrous oxide emissions and inducing priming effects on native soil organic matter (SOM). Microbes release chemical signals into the environment to monitor their own population density to regulate behaviors, and interference with microbial cell-cell signaling was proposed as one of the potential mechanisms responsible for the charcoal-induced negative effects. Our prior research indicated that charcoal can sorb these apolar signaling compounds and effectively disrupted cell-cell communication due to its large active surface area. We hypothesized that charcoal pH could also affect the lifetime of some chemical compounds that microbes use for cell-cell signaling on times scales relevant to growth and communication. To test this idea, we examined the extent and rate of ten charcoals with a wide range of physicochemical properties on signaling reduction of an acyl-homoserine lactone (AHL), N-3-oxo-dodecanoyl-L-homoserine lactone, used by many gram-negative bacteria for quorum sensing using both bioassay and chemical sorption approaches. Our results indicated that charcoal decreased the bioavailable level of AHL through a combination of sorption and pH-dependent hydrolysis of the lactone ring, and we showed that the kinetics of hydrolysis can exceed those of sorption. These findings implicate charcoal surface area and alkalinity as properties that could be tuned to regulate the degradation rates of cell-cell signaling molecules in soils. The relative contribution of these two mechanisms (sorption and hydrolysis) to charcoal quenching of microbial communication is expected vary across charcoal types and microbial species due to variability in the molecules used for cell-cell signaling.

Charcoal quenching of cell-cell communication can arise from a combination of signaling molecule hydrolysis and sorption

251st National Meeting (2016)

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