Anaerobic digestion is a microbiological technology that converts biomass wastes into biogas, achieving both waste treatment and bioenergy production. Accumulation of volatile fatty acids (VFA) during acidogenesis, particularly propionate, often causes upset or failure of digesters. Early detection and monitoring of propionate concentration in digesters allow for just-in-time interventions to prevent irreversible costly process breakdown. In an attempt to develop a rapid method of measuring propionate concentration and bioavailability, we constructed a genetic construct for specific detection of bioavailable propionate. The genetic construct was constructed by transcriptional fusion of the regulatory gene (prpR) and the promoter of the prp operon (P-prpB) of Escherichia coli W3110 with the reporter gene cassette luxCDABE. When the genetic construct was carried on a plasmid and transformed into E. coli (referred to as plasmid-based biosensor), it resulted in stronger emission of luminescence than when it was inserted into the chromosome of E. coli (referred to as chromosome-based biosensor). The biosensor responded specifically to propionate. The luminescence signal increased linearly with increasing concentration of propionate from 1 to 10 mM. The utility of the biosensor was evaluated using samples collected from anaerobic digesters. Once instrumented in future studies, the whole-cell bacterial biosensor developed in this study may provide an alternative technology for real-time detection and measurement of propionate in digesters. (C) 2014 Wiley Periodicals, Inc.