Bioconversion Of Crude Glycerol To 1,3-Propanediol By Synthetic Microbial Consortia

Compared with pure culture,microbial consortium fermentation is more and more advanced and important with the development of Omics Technology.Microbial consortium,with characteristics of diversity,stability and robustness against environmental fluctuations and excellent performances,may be an option to deal with situations such as?1?the need to use complex and a broad range of carbon sources that is impossible for single organism;?2?side products can accumulate with a single organism that can inhibit growth and productivity;and?3?the need to construct long biosynthetic pathways that may result in low productivity with a single organism.However,the problems of functional redundancy,integration of dominant functions and stability of microbial consortium have not been effectively solved,which still restrict the application of microbial consortium fermentation.Therefore,this paper on the basis of the above mentioned facts is divided into two aspects:One is discovering new functional consortia and excavating new functions of consortia,the other is construction of a functional integrated,efficient and stable consortium for 1,3-PD production.Firstly,an anaerobic microbial consortium for conversion of crude glycerol was selected and its 1,3-propanediol production capacity was evaluated.The consortium was obtained from wastewater samples by 35 serial transfers.The physiological and biochemical characteristics of DUT08 were determined,indicated that the consortium consisted of Clostridium?85%-95%?,Escherichia?5%-15%?and Klebsiella?0.007%-0.012%?.Three strains,C.butyricum DUT1,K.pneumonia DUT2 and E.coli DUT3 were isolated from DUT08.Secondly,a mutually beneficial relationship between C.butyricum DUT1 and E.coli DUT3 has been discovered during anaerobic fermentation.There is not only competitive relationship between C.butyricum DUT1 and K.pneumonia DUT2,commensalism can also be observed.Furthermore,E.coli DUT3 can attenuate the competitive relationship between K.pneumonia DUT2 and C.butyricum DUT1 while strengthening commensalism relationship.In a batch fermentation by microbial consortium DUT08 under microaerobic conditions with no nitrogen supply,43.20 g/L 1,3-PD with a yield of 0.39 g/g and a productivity of 0.98g/?L.h?were produced.In contrast,61.49 g/L 1,3-PD?0.55 g/g and 2.46 g/?L.h??was produced under anaerobic conditions with nitrogen supply for 3h,with increasing 1,3-PD production by 42.34%,yield by 41.03%and productivity by 151.02%.What's interesting is that anaerobic fermentation can still be performed in the short-term?3 h?,low N₂ sparging?0.02 vvm?condition.Finally,synthetic microbial consortium was designed and constructed based on the structure of DUT08 and the relationship between the three strains.These results demonstrated the potential advantage of symbiosis and provided a promising strategy for 1,3-PD prodction.During the fermentation process,lower dissolved oxygen tolerance,substrate inhibition and product inibition restricted the growth of C.butyricum DUT1.The function of K.pneumonia DUT2 and E.coli DUT3 was found to not only deplete oxygen and provide anaerobic environment for C.butyricum DUT1,but also remove the inhibition of substrates and products on C.butyricum DUT1.Synthetic microbial consortia will have the best production performance in this study,the highest 1,3-PD concentration was 81.39 g/L when fed-batch fermentation is carried out under anaerobic condition.The concentration of 1,3-PD still has77.68 g/L in the short-term?3 h?,low N₂ sparging?0.02 vvm?condition.However,C.butyricum DUT1 produces only 61.72 g/L of its main product when fermentation lasted for53h under the same condition.These results demonstrated the potential advantage of symbiosis and also provided a promising strategy for 1,3-propandiol fermentation.