J. Chen, B. Hu, S. Wang, W. Hu, L. Liu, J. Liu, W. Li
Institute of Modern Physics, Chinese Academy of Sciences,
Keywords: citric acid, mutant of aspergillus niger, carbon ion irradiation, corn meal hydrolysate
Summary:Citric acid fermentation is one of the largest biotechnological industries  and Aspergillus niger is of a good potential to produce citric acid. The annual citric acid production through fermentation is estimated at 7.0X105 tonand the industrial demand of citric acid is in steady increase  . To obtain high production scale of citric acid, a possible strategy is to improve microbial production strain. Therefore, it is vital to enhance the citric acid production capacity of Aspergillus niger. Strains with superior characters, such as enhanced citric acid production and high fermentation index have been selected after subjecting the genetic material to physical or chemical mutagenic agents . Heavy ion-induced mutation is a unique method of physical mutation. With high LET (linear energy transfer) and RBE (relative biological effectiveness), it can induce single- or double-strand DNA breaks with low reparability in bombarded tissue and mighty potency to improve the mutation rate and broaden the mutation spectrum. Progresses have been made at Institute of Modern Physics, Chinese Academy of Science (IMP, CAS) in heavy ion mutation breeding of Gentamicin, alcoholresistant yeast and Streptomyces Avermitilis . We report here the selection of mutants of A.niger for hyper yield of citric acid irradiated by 12C6+ beams form Heavy Ion Research Facility of Lanzhou (HIRFL). Among these mutants, mutant H4002 had a higher yield of citric acid production than the parental strain in a 250-ml shaking flash. The expanded submerged experiments in a bioreactor were also carried out for mutant H4002, and showed that (177.7–196.0) g/L citric acid was accumulated by H4002 through exploiting corn meal hydrolysate (containing initial 200.0–235.7 g/L sugar) with the productivity of (2.96–3.27) g/(L·h). Especially, when the initial sugar concentration was 210 g/L, the best economical citric acid production reached (187.5±0.7) g/L with a productivity of 3.13 g/(L·h). It was observed that mutant H4002 can utilize low-cost corn meal as a feedstock to efficiently produce citric acid. These results imply that the H4002 strain has the industrial production potentiality for citric acid and offers strong competition for the citric acid industry. Reference 1. Rohr M. Food Technol Biotech, 1998, 36: 163–171. 2. Ikram-UI H, Ali S, Qadeer M A. Bioresource Technol, 2004,93: 125–130. 3. Parekh S, Vinci V A, Strobel R J. Appl Microbiol Biot, 2000, 54: 287–301. 4. Hu W, Chen J-H, Li W-J, et al. Nuclear Science and Techniques, 2014, 25: 020302-1-4.