Total RNA samples were prepared as previously described (Sze et al., 2011 (link)). To produce cDNA, 300 ng of RNA was reversely transcribed using AMV reverse transcriptase (Promega, Madison, WI). For reverse transcription-PCR (RT-PCR), 1 μl of cDNA was PCR amplified with different pairs of primers using Taq DNA polymerase (Qiagen). The quantitative PCR (qPCR) analysis of fliF (primers P9/P10), flgG (primers P11/P12), flgE (primers P13/P14) and flaB (primers P15/P16) transcripts was carried out using iQ SYBR green Supermix and MyiQ thermal cycler (Bio-Rad Laboratories, Hercules, CA). The transcript of the enolase gene (eno, bb0337, primers P17/P18) was used as an internal control to normalize the qPCR data as described before (Sal et al., 2008 (link)). The results were expressed as threshold cycle (CT) value between the wild-type and mutant strains. All of the primers for RT-PCR and qRT-PCR are listed in Table S1.