ABSTRACT “ Dehalococcoides ” bacteria can reductively dehalogenate a wide range of halogenated organic pollutants. In this study, DNA microarrays were used to monitor dynamic changes in the transcriptome as “ Dehalococcoides ethenogenes” strain 195 transitioned from exponential growth into stationary phase. In total, 415 nonredundant genes were identified as differentially expressed. As expected, genes involved with translation and energy metabolism were down-regulated while genes involved with general stress response, transcription, and signal transduction were up-regulated. Unexpected, however, was the 8- to 10-fold up-regulation of four putative reductive dehalogenases (RDases) (DET0173, DET0180, DET1535, and DET1545). Another unexpected finding was the up-regulation of a large number of genes located within integrated elements, including a putative prophage and a multicopy transposon. Finally, genes encoding the dominant hydrogenase-RDase respiratory chain of this strain (Hup and TceA) were expressed at stable levels throughout the experiment, providing molecular evidence that strain 195 can uncouple dechlorination from net growth.