Development of bacterial biosensor for sensitive and selective detection of acetaldehyde

Acetaldehyde is a human carcinogen and widely existed in alcoholic beverages and polluted air. In this study, a simple, fast, convenient and sensitive acetaldehyde biosensor was developed based on an acetaldehyde dehydrogenase (AldDH) bacteria surface display system. The whole-cell catalyst facilitated the dehydrogenation of acetaldehyde, while coenzyme NAD+ was reduced and the resultant NADH can be detected spectrometrically at 340 nm. The correct location of AldDH on the bacteria surface was confirmed by the subcellular fraction and immunofluorescence analysis. By comparing the fusion protein expression level and whole-cell activity, the proper display system for anchoring AldDH on the cell surface was obtained. The results of kinetics analysis towards both surface-displayed AldDH and intracellular expressed AldDH demonstrated that the mass-transport resistance was dramatically alleviated by cell-surface display strategy. Under optimal conditions, AldDH-surface display strain with the highest whole-cell activity (3.41 +/- 0.3 mU/OD600) was applied to spectrophotometry acetaldehyde detection system. An excellent linear relationship between the increases of absorbance at 340 nm and acetaldehyde concentration over the range from 1 mu M to 300 mu M was reached. The proposed approach offered adequate sensitivity for the detection of acetaldehyde at 0.33 mu M. Most importantly, the developed biosensor showed the narrowest substrate specificity towards acetaldehyde, which has been employed for quick determination of acetaldehyde in real samples with good accuracy. The total detection time was within 20 min. The method reported here provided a simple, rapid, and low-cost strategy for the sensitive and selective measurement of acetaldehyde. Therefore, genetically engineered cells may find broad application in biosensors and biocatalysts.