qRT-PCR analysis of the transcriptional level of otrC in S. rimosus mutants. A: The transcriptional level of otrC in M4018/pSEC at 24 h (light gray) and 96 h (dark gray) during OTC fermentation, where M4018/pSET152 was used as the control. B: The transcriptional level of otrC in SR16/pSEC at 24 h (light gray) and 72 h (dark gray) during OTC fermentation, SR16/pSET152 was used as the control. S. rimosus cells were collected at different developmental stages during culture in fermentation medium. RNA extraction and quality control is described in the Materials and Methods. Three housekeeping genes, 16S rRNA, hrdB and zwf1, were used as the reference genes for qRT-PCR analysis.