| In recent years,the production of propionic acid by microbial fermentation has received more and more attention.In order to relieve the feedback suppression phenomenon in the fermentation process,the researchers carried out a lot of research from the aspects of medium optimization,metabolic pathway and fermentation process regulation.However,the performance of the strain produced by Propionibacterium could directly affect the fermentation efficiency of propionic acid.So screening an excellent acid-resistant strain for establishment of coupling process for fermentation separation and industrial production is of great significance.In this paper,the acid-resistant strains with excellent production performance were screened by pressure screening method based on the laboratory preservation of Propionibacteria freudenreichii F-0 and Propionibacteria acidipropionici P-0 as a starting strain.The main results of this paper are as follows:1.The laboratory storage of P.freudenreichii F-0 as the original strain,the method of pressure screening was used to increase the environmental selection pressure(propionic acid concentration),and a strain of P.freudenreichii resistant to 50g/L propionic acid was obtained by using F-0 as the starting strain in the laboratory preservation.which provided excellent strains for the production of propionic acid/vitamin B12 by the combination fermentation of P.freudenreichii.2.The laboratory storage of P.acidipropionici P-0 as the original strain,a strain of P.acidipropionici P-10 with acid-resisting and acid-producing ability was obtained by pressure screening method.In the shake flask fermentation 168 h,the yield of propionic acid was 49.64 g/L and the rate of propionic acid was 0.3 g/(L·h),which was 53.04% higher than that of P-0.At the same time,the fermentation results of 7L fermentor showed that the propionic acid concentration reached 55.63g/L and the rate of propionic acid was 0.33g/(L·h)when the fermentation period of the acid-resistant strain P-10 was 168 h,a shake flask fermentation was increased by 10%.3.The production stability of P.acidipropionici P-10 was investigated.The results showed that the propionic acid production of the acid-resistant strain P-10 did not decrease significantly after 8 times of continuous delivery,showing good production stability.4.The effects of succinic acid on the fermentation of P.acidipropionici P-10 were investigated.The results showed that when 15 g/L and 20 g/L succinic acid were added to the medium,the cells growth of the acid-resistant strain P-10 was not affected.the production capacity of P-0 was decreased by 16.38% and 17.01% respectively,and the succinic acid production capacity decreased by 33.32% and 36.07% respectively,while the yield of propionic acid and succinic acid was not decreased.The ability of cell growth was also reduced by 30.32% and 35.50%.Compared with the original strain P-0,the ability of the acid-resistant P-10 to tolerate succinic acid was obviously improved.5.The application of P.acidipropionici P-10 in batch fed fermentation was investigated.When the fermentation to 84 h and 156 h,respectively,the second inoculation,that is,access to 10% of the fresh seed liquid,The results showed that the concentration of propionic acid reached 60.39 g/L and 54.35 g/Lat the end of fermentation respectively,which were higher than those of the acid resistant strain P-10 without secondary fermentation,especially at 84 h for secondary inoculation,the propionic acid concentration was 17.74% higher than that in the batch fermentation.In addition,the propionic acid rate of acid-resistant strain P-10 was 74.99% higher than that of the original strain P-10,and the application prospect of acid-resistant strain P-10 was further verified. |
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