Monitoring of GFP-Tagged Bacterial Cells

In recent years, molecular tools have been developed to identify and quantify specific microbial cells, or specific microbial activittes, in mixed populations (1 , 2 ). These tools are especially valuable for analysis of specific bacteria in complex environmental samples. Increasingly, research has concentrated on the development of marker genes for tagging a particular bacterial species of interest, so that the cells can be spectfically identified and monitored (1 —3 ). For example, the genes encoding bacterial luciferase (luxAB) or firefly luci-ferase (lux) have been found to be very useful markers, since tagged cells can be detected on the basis of their bioluminescent phenotype. Other examples of genes specifically used to mark bacteria include metabolic markers, such as lacZY )(β- galactosidase and lactose permease), gusA (β-glucuronidase), and xylE (2,3-catechol dioxygenase), which are detected on the basis of unique colored products formed after growth of the cells on specific media (1—3).