Use of a Whole-cell Biosensor and Flow Cytometry to Detect AHL Production by an Indigenous Soil Community During Decomposition of Litter

Quorum sensing, mediated by acylated homoserine lactones (AHLs), is well described for pure culture bacteria, but few studies report detection of AHL compounds in natural bacterial habitats. In this study, we detect AHL production during a degradation process in soil by use of whole-cell biosensor technology and flow cytometry analysis. An indigenous soil bacterium, belonging to the family of Enterobacteriaceae, was isolated and transformed with a low-copy plasmid harboring a gene encoding an unstable variant of the green fluorescent protein (gfpASV) fused to the AHL-regulated P(luxI) promoter originating from Vibrio fischeri. This resulted in a whole-cell biosensor, responding to the presence of AHL compounds. The biosensor was introduced to compost soil microcosms amended with nettle leaves. After 3 days of incubation, cells were extracted and analyzed by flow cytometry. All microcosms contained induced biosensors. From these microcosms, AHL producers were isolated and further identified as species previously shown to produce AHLs. The results demonstrate that AHL compounds are produced during degradation of litter in soil, indicating the presence of AHL-mediated quorum sensing in this environment.