A dip-stick type biosensor using bioluminescent bacteria encapsulated in color-coded alginate microbeads for detection of water toxicity

The use of genetically engineered bioluminescent bacteria, in which bioluminescence is induced by different modes of toxic action, represents an alternative to acute toxicity tests using living aquatic organisms (plants, vertebrates, or invertebrates) in an aqueous environment. A number of these bacterial strains have been developed, but there have been no attempts to develop a hand-held type of biosensor for monitoring or identification of toxicity. We report a facile dip-stick type biosensor using genetically engineered bioluminescent bacteria as a new platform for classification and identification of toxicity in water environments. This dip-stick type biosensor is composed of eight different optically color-coded functional alginate beads that each encapsulates a different bioluminescent bacterial strain and its corresponding fluorescent microbead. These color-coded microbeads exhibit easy identification of encapsulated microbeads, since each microbead has a different color code depending on the bioluminescent bacterial strain contained and improved cell-stability compared to liquid culture. This dip-stick type biosensor can discriminate different modes of toxic actions (i.e. DNA damage, oxidative damage, cell-membrane damage, or protein damage) of sample water tested by simply dipping the stick into the water samples. It was found that each color-coded microbead emitted distinct bioluminescence, and each dip-stick type biosensor showed different bioluminescence patterns within 2 hours, depending on the toxic chemicals contained in LB medium, tap water, or river water samples. This dip-stick type biosensor can, therefore, be widely and practically used in checking toxicity of water in the environment primarily in situ, possibly indicating the status of biodiversity.