The Key Technologies Of Synthesizing Typical Fermentation Products Under Different Substrates Feedings/Oxygen Supply And Reductive Power Regulation Strategies

China is the top industrial fermentative production country, with the largest fermentative products yields in the world. However, the typical low-profit bulk fermentation products occupy more than 50% in the market. It is extremely important to improve the productivity and economics of the industrial fermentation processes for their future developments. Besides the methods of molecular modification and strains breeding/screening, fermentation/metabolic engineering techniques are alternative and important ways for improving performance of fermentation processes. The common problems in bulk fermentative products synthesis processes are: low products yields and substrate utilization efficiency; high raw materials costs; low fermentation performance when directly using cheap raw materials; and difficulties in direct control/optimization of the fermentation processes, particularly the on-line based one. In this dissertation, with the typical aerobic(CPC/glucoamylase) and anaerobic(butanol/acetone) fermentation processes as the prototypes, by using the proposed key technologies of synthesizing typical fermentation products under different substrates feedings/oxygen supply and reductive power regulation strategies with cheaper raw materials, improvement of those processes in the terms of their productivity and economics were pursued/explored. The major results were summarized as follows:(1) In CPC fermentation by A. chrysogenum, enhanced CPC titer is generally achieved by feeding pure soybean oil and supplying more NADPH by it, but CPC yield on soybean oil was very low. In addition, in this case, the bad DO control performance, low O2 transfer coefficient kLa and soybean oil supplemental rate yielded lower CPC titer and by-product(DAOC) accumulation. Co-feeding soybean oil/glucose mixture could solve the problems. Theoretical analysis revealed that, in this case, the low-valued glucose could enter pentose phosphate pathway directly to supply NADPH and most of soybean oil could be used for CPC synthesis leading to an enhanced CPC yield; DO, k La and soybean oil feeding rate could be maintained at higher levels to avoid DAOC accumulation; CPC yield on soybean oil and CPC titer enhanced from 12.9% and 25.32 g·L-1 to 23.5% and 37.0 g·L-1, respectively; the economics of CPC fermentation was markedly enhanced.(2) The effects of different feeding strategies on glucoamylase production by A. niger were investigated with maltose syrup and ?-lactose as the feeding carbon sources. A novel metabolic activity-based three-stage rate-varied substrate feeding strategy was thus proposed. With the feeding strategy, RQ could be controlled around 0.60 and OUR kept at higher level during the feeding stage, and final glucoamylase activity reached 118,900 U·m L-1 with an increment of 64% in comparison with that of using DO-Stat feeding method. The feasibility of using different low-valued carbon source for glucoamylase production was also studied. With cornstarch hydrolysate as the feeding carbon source, final glucoamylase activity reached the highest level of 156,400 U·m L-1 and the raw materials cost could be reduced by ~61%.(3) Acetone-Butanol-Ethanol fermentation(ABE fermentation) by C. acetobutylicum featured with low butanol concentration and butanol/acetone ratio(B/A). Butanol concentration and B/A could be significantly enhanced by the operation strategy of co-culturing C. acetobutylicum/S. cerevisiae integrated with slight butyrate addition. In this thesis, combining the experimental data, a mathematical model describing the rates of substrate consumption, products synthesis and NADH regeneration was developed to elucidate the mechanism of performance improvement when using the co-culturing based ABE fermentation mode. The results indicated that the proposed ABE fermentation mode could increase NADH regeneration rate required for butanol synthesis in C. acetobutylicum and glucose utilization ability of the cells simultaneously; enhance the tolerance of C. acetobutylicum against high butanol environment indirectly. Butanol concentration and B/A in anaerobic fermentor could reach higher levels of 15.74 g·L-1 and 2.83, with the increments of 35.3% and 42.9% as compared with those of control. The two indexes could also reach high levels of 16.34 g·L-1 and 3.02 when using concentrated butyrate fermentative supernatant to replace synthetic butyrate. Products purification cost could be largely reduced due to the enhanced butanol and ABE concentrations. Economic evaluation indicated the co-culturing based ABE fermentation with the supernatant addition has industrial application potential.(4) ABE fermentation products are basically the mixture of butanol and acetone. The economics and flexibility of ABE fermentation strongly rely on evaluating acetone as a valuable platform chemical and powerful biofuel. Both acetone and butanol concentrations could be elevated by the C. acetobutylicum/S. cerevisiae co-culturing system integrated with small amount acetate exogenous addition. A mathematical model suitable for evaluating this process was also developed to elucidate the metabolic mechanism and reasons for acetone/butanol concentrations enhancements. The results indicated that the proposed process could increase glucose utilization ability of C. acetobutylicum; control NADH regeneration rate at moderately low level to direct more carbon source into acetone synthesis route without sacrificing butanol production; and enhance the tolerance of C. acetobutylicum against high butanol environment by intracellular accumulating favorable amino acids. Final acetone and butanol concentrations in fermentor could reach higher levels of 8.27 g·L-1 and 13.91 g·L-1 simultaneously with the increments of 41% and 20% as compared with those of control.(5) On the basis of C. acetobutylicum/S. cerevisiae co-culturing system with slight acetate addition, a novel strategy incorporating glucose/acetate co-substrate with glucose limitation was proposed to run ABE fermentation. In this case, acetone production could be significantly elevated while NADH dependent butanol synthesis rate was adequately restricted through glucose limitation by decreasing initial glucose concentration and adaptively/consecutively adding acetate/S. cerevisiae during solventogenic phase; acetone production ability of C. acetobutylicum could be fully utilized by delaying butanol inhibition occurrence time. The proposed strategy could arbitrarily control or maximize acetone concentration and acetone/butanol ratio in the ranges of 6-12 g·L-1 and 0.5-1.0, and their maximum values reached the levels of 11.74 g·L-1 and 1.02 without sacrificing butanol production. This strategy would potentially promote bio-acetone productions using biomass to replace fossil resources and realize products diversity or flexibility of ABE fermentations.