Optimization of D-ribose production with a transketolase-affected Bacillus subtilis mutant strain in glucose and gluconic acid-based media

When the transketolase-deficient and D-ribose-producing Bacillus subtilis strain ATCC 21951 was grown in a glucose (200 g l-1)-based medium (Kintaka et al. 1986), only 11 g l-1 D-ribose was synthesized, in addition to acetic acid (12 g l-1) and acetoin plus 2,3-butanediol (24 g l-1), within 1 week of fermentation. After optimizing the process conditions at 21 fermentor scale (simplified medium composition, pH 5.0 or 6.0, highly oxidative (1000 rev min-1, 3 vvm)), 40 g l-1 D-ribose was obtained from 200 g l-1 D-glucose, in addition to 14.5 g l-1 acetoin, during 1 week of fermentation. By partially substituting D-glucose with D-gluconic acid (100 g l-1 D-glucose plus 50 g l-1 D-gluconic acid) under highly oxidative (1000 rev min-1, 3 vvm) and pH-controlled (pH 6.5) conditions, D-ribose productivity increased 145 g l-1) and acetoin formation (7.5 g l-1) dropped, as did the fermentation time (3.5 d). The mixed carbon substrate procedure here developed provides an excellent alternative to the less efficient glucose-based processes described so far.