A new diagnostic method for soil-borne disease using a microbial biosensor.

We have developed a new system for the rapid diagnosis of soil-borne diseases, consisting of two biosensors. The system was constructed using equal quantities of two different microbes, each individually immobilized on an electrode. These two sensors were coupled as a dual sensor system and used for simultaneous measurements. Measurements were carried out by immersing the microbial sensors in a soil extract. When microbial respiration increased with the assimilation of organic compounds in the sample, the decrease of the dissolved oxygen concentration was measured with an oxygen electrode. Initially, three pathogen-infested soils were compared to two non-diseased soils using the system. The ratio of responses to both non-diseased soils was higher than that to infested soils. Subsequently, we used the biosensor system to investigate the effect of six antagonists on the inhibition of four diseases. The correlation between the development of symptoms and ratio to responses was estimated. The ratio between the responses of the two sensors correlated with symptoms, except for two samples where the antagonist promoted the disease's development.