A microarray targeting four sequenced strains in the Dehalococcoides (Dhc) genus was used to analyze gene expression in a robust long-term trichloroethene (TCE)-degrading microbial community (designated ANAS) during feeding cycles that involve conditions of periodic substrate supply. The Dhc transcriptome was examined at three time-points throughout a batch feeding cycle: T1 (27 h) when TCE, dichloroethene (DCE), and vinyl chloride (VC) were present; T2 (54 h) when only VC remained; and T3 (13 d) when Dhc had been starved of substrate for nine days. 90% of the Dhc ORFs that were detected in the ANAS DNA were found to be expressed as RNA sometime during the time course, demonstrating extraordinary utilization of the streamlined genome. 97% of these transcripts were differentially expressed during the time course, indicating efficiency of transcription through regulation in Dhc. Most Dhc genes were significantly down-regulated at T3, responding to a lack of substrate as would be expected. The tceA and vcrA genes, which code for proteins with known chlorinated ethene reduction functions, were highly expressed at both T1 and T2, whereas two other putative reductive dehalogenase genes (DET0173 and DET1545) were most highly expressed at T2, likely in response to the presence of VC. Hydrogenases were most highly expressed at T1, reflecting their important role in accumulating electrons used to initiate reductive dechlorination and other biosynthesis pathways. Cobalamin transport genes were preferentially expressed at T2, reflecting an increase in corrinoid transport as chloroethenes were degraded and a decrease in activity of the transport system after dehalogenation was complete. This is the first application of a microarray targeting a known genus, including both core genomes and identified strain-specific genes, applied to improve our understanding of transcriptional dynamics within an undefined microbial community. Replicate samples were independently collected, and simultaneously but individually extracted, fragmented, labeled, and hybridized to arrays. Three DNA samples (one from each of the three replicate cycles) and nine RNA samples (one from each of the three time-points in each of the three replicate cycles) were prepared for microarray analysis.