title: Enhanced acid tolerance of Rhizopus oryzae during fumaric acid production.
abstract: Ensuring a suitable pH in the culture broth is a major problem in microorganism-assisted industrial fermentation of organic acids. To address this issue, we investigated the physiological changes in Rhizopus oryzae at different extracellular pH levels and attempted to solve the issue of cell shortage under low pH conditions. We compared various parameters, such as membrane fatty acids' composition, intracellular pH, and adenosine triphosphate (ATP) concentration. It was found that the shortage of intracellular ATP might be the main reason for the low rate of fumaric acid production by R. oryzae under low pH conditions. When 1 g/l citrate was added to the culture medium at pH 3.0, the intracellular ATP concentration increased from 0.4 to 0.7 µmol/mg, and the fumaric acid titer was enhanced by 63% compared with the control (pH 3.0 without citrate addition). The final fumaric acid concentration at pH 3.0 reached 21.9 g/l after 96 h of fermentation. This strategy is simple and feasible for industrial fumaric acid production under low pH conditions.
authors.affiliation: State Key Laboratory of Material-oriented Chemical Engineering College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, No. 30 Puzhu Road, Nanjing, 211816, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.forename: Chunwei
authors.initials: C
authors.lastname: Lv
authors.forename: Qing
authors.initials: Q
authors.lastname: Xu
authors.forename: Shuang
authors.initials: S
authors.lastname: Li
authors.forename: He
authors.initials: H
authors.lastname: Huang
authors.forename: Pingkai
authors.initials: P
authors.lastname: Ouyang
mesh_terms: D000143:Acids / Q000378:metabolism*; D003470:Culture Media / Q000378:metabolism*; D005650:Fumarates / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D012233:Rhizopus / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000143:Acids; D003470:Culture Media; D005650:Fumarates; C032005:fumaric acid