Reference genes for quantitative, reverse-transcription PCR in Bacillus cereus group strains throughout the bacterial life cycle

► Re-analysis of microarray expression data is a promising approach to identify suitable reference genes for RT-qPCR. ► gatB_Yqey, rpsU and udp are stably expressed reference genes in the life cycle of a B. cereus and a B. thuringiensis strain. ► gatB_Yqey may be used as a single reference gene when studying large expressional changes in the bacterial life cycle. ► Normalization of gene expression data using non-validated reference genes is likely to lead to erroneous results.