Our transcriptome map of H. somni identified expression from 1636 (approximately 80%) of the predicted genes. The expressed genes were distributed evenly across all TIGRFAM functional categories (Table S1 ). The transcriptome map allowed identification of operon structures at a genome scale, critical for identifying co-expressed genes and for understanding coordinated regulation of the bacterial transcriptome. We identified co-expression for 452 pairs (total 730 genes) of H. somni genes ( Table S2 ) that were transcribed together and constituted a minimal operon. By joining consecutive overlapping pairs of co-expressed genes, we identified 278 distinct transcription units (Table S3) .