Specific OTC production of S. rimosus strains. A: An extra copy of otrC was introduced into the S. rimosus M4018 chromosome using the recombinant integrative vector pSEC (white circles). The otrC disruption mutant of M4018 was constructed using the temperature-sensitive recombinant plasmid pKCΔotrC (white stars). M4018/pSET152 (black squares) served as the control. B: An extra copy of otrC was introduced into the chromosome of S. rimosus SR16 using the integrative vector pSEC (white diamonds). The otrC disruption mutant of SR16 was constructed using the temperature-sensitive plasmid pKCΔotrC (white hexagons). SR16 that carried the empty pSET152 plasmid was used as the control (black triangles). S. rimosus strains were grown in MS plates, spores were inoculated into GYCS medium to the final concentration of 1 × 106 spores per ml, after which they were cultured at 28°C on a rotary shaker (260 rpm) for 72 h; 1% seed culture was transferred into SC medium cultured at 30°C on a rotary shaker (260 rpm) for 7 d. OTC was measured by HPLC. Vertical error bars correspond to the standard error of the mean of three replicated cultures.