We compared our experimentally identified co-expressed genes with computationally predicted operons. The overlap between computational prediction of co-expressed genes using DOOR [24] and this study was 86% (394 gene pairs) (Table S4) . Thus, our dataset validates expression of 394 computational gene-pair predictions. We identified 59 new gene pairs that are co-expressed and were not predicted by DOOR, which could be part of unidentified, new operon structures. For example, further in-depth analysis indicated a new operon consisting of three genes: HSM1354, HSM1355 and HSM1356, annotated as ribosomal protein L20, ribosomal protein L35, and translation initiation factor IF-3 respectively, which were not predicted computationally ( Figure 5 ). The orthologs of these genes are well known to form a functional operon of ribosomal proteins (IF3-L35-L20) in Escherichia coli [25] .