Detection of Firefly Luciferase-Tagged Bacteria in Environmental Samples

In recent years, several molecular methods have been developed for tracking genetically engineered microorganisms (GEMS) in environmental samples (1 –3 ) The majority of the methods are based on monitoring of bacteria tagged with a marker gene, which provides the bacteria with a unique phenotype or DNA sequence for detection. The challenge has been to design molecular monitoring procedures that are quantitative in order to estimate the biomass of a specific microbial population in natural samples (4 ). Quantitation of few cells of a given species becomes especially complicated when taking into account the vast natural diversity of microorganisms in nature; for example, it has been estimated that a single gram of soil contains thousands of distinct genotypes (5 ). Therefore, it is important to have methods that are sensitive and specific for the tagged bacterium, and that can be used to quantitate the number of specific cells present in the sample.