Studies On Efficient Bioproduction Of Propionic Acid And Acrylic Acid With Anaerobic Bacteria

Propionic acid and acrylic acid are two important bulk chemicals which now are mainly produced by the multiple chemical reactions with the downstream of petrochemical products. Due to the non-renewable and quick consumption of fossil resources, the production of these two bulk chemicals by economic micrograms with renewable resources has an increasing attracts in industry.Propionic acid is a useful platform chemical, and can be a potential precursor for the synthesis of acrylic acid by chemical methods. In the present work, Propionibacterium acidipropionici(P. acidipropionici) CGMCC1.2230was selected due to its powerful ability of producing propionic acid in a5L fermentation tank and the fibrous-bed bioreactor (FBB). In order to optimize cell immobilization in FBB, the mechanism and factors controlling cell adhesion on wood fibers and cotton fibers were studied. With the wood fiber materials, the propionic acid concentration, yield and productivity in the batch fermentation were28g/L,0.55g/g and0.36g/(L·h), respectively. By using cotton fibers as immobilization matrix, the propionic acid concentration, yield and productivity were22.4g/L,0.51g/g and0.96g/(L·h), respectively. To increase final propionic acid concentration, the feeding strategy of glucose was adopted in the FBB system. The propionic acid concentration was increased to51.2g/L, and the yield (0.43g/g) and productivity (0.71g/(L·h)) were still high in this fed-batch fermentation.The utilization of sugarcane bagasse hydrolysate to production propionic acid was tried here. The concentration of propionic acid in repeat batches was12.9g/L with a productivity of0.88g/(L·h) by using sugarcane bagasse hydrolysate in the repeat-batch fermentations, and the yield was0.29g/g (reducing sugars). A fed-batch strategy was employed to improve the utilization of sugarcane bagasse hydrolysate by using glucose as the feeding substrate. The propionic acid concentration was increased to58.8g/L with the yield of0.37g/g in254h fed-batch fermentation. More than60%of xylose in sugarcane bagasse hydrolysate was utilized, whereas the existing glucose was totally consumed. Then the comparison of propionic acid production between in series and parallel connected multi-FBB systems was carried out to study the effect of multiple reactors. The results showed the propionic acid concentration (23.4g/L) in series connection mode was higher than that in parallel mode, and the product concentration could be improved up to58.4g/L in the fed-batch fermentation with the parallel-connection multi-FBB reactors.This paper was also devoted to construct a microbial fuel cell (MFC) with Clostridium propionicum as an alternative way to produce acrylic acid which might be coupled with electricity generation. Electricity was generated with cysteine and resazurin in the anode chamber as mediators, and K3Fe(CN)6as the cathode electron acceptor. In the salt-bridge MFC, the output voltage and power generation were116mV and21.78mW·m-2respectively when the system resistance was1000Ω. Batch experiments and cyclic voltammograms indicated that the main mechanism of power production was the electron transfer facilitated by extra mediators in the system. In the salt-bridge MFC system, acrylic acid was produced together with electricity generation from the resting cells of C. propionicum with the aide of the methyl-blue as the mediator.Further metabolic synthesis of acrylic acid in E. coli was proposed according to metabolic engineering strategy. In this paper, a mutated propionyl-CoA synthase which could catalyze3-HP to generate acrylyl-CoA was cloned to E. coli Rossetta (DE3) by using genetic engineering. A high expression of this soluble protein were obtained, and the possible functional of the mutated propionyl-CoA syntheses for the production of acrylic acid in this recombinant E. coli was discussed.The systematical investigation for high efficient production of propionic acid and exploring the new strategy of acrylic acid synthesis in anaerobic bacteria will lay one base for large-scale bioproduciton of these two important short-chain organic acid in the future...