Optimal aerobic cultivation method for 1,4-dihydroxy-2-naphthoic acid production by Propionibacterium freudenreichii ET-3.

To investigate the effects of oxygen supply on Propionibacterium freudenreichii ET-3 metabolism and 1,4-dihydroxy-2-naphthoic acid (DHNA) production in detail, the strain was cultured by switching from anaerobic condition to aerobic condition at 72 h (termed anaerobic-aerobic switching culture hereafter) employing different oxygen transfer rates (OTRs) in the range of 0.08-0.90 mg/(l.h). It was found that a 0.08 mg/(l.h) OTR could not change the metabolism or improve the DHNA production of P. freudenreichii ET-3. When the OTR was in the range of 0.23-0.66 mg/(l.h), propionate, which inhibits DHNA production significantly, was consumed during the aerobic phase. Final DHNA concentration increased to 0.22 mM, irrespective of OTR. When the OTR was 0.90 mg/(l.h), a sudden increase in dissolved oxygen (DO) concentration during the aerobic phase resulted in a sudden decrease in DHNA concentration. To attenuate the stresses caused by propionate and oxygen exposure, we designed an optimal cultivation in which the anaerobic and aerobic phases were repeated three times alternately. As a result, propionate concentration was maintained below the level that inhibits DHNA production, and no DO concentration was detected throughout the culture. The final DHNA concentration in this culture was 0.33 mM, which is 2.7-fold that in the anaerobic culture and 1.5-fold that in the anaerobic-aerobic switching culture.