An Artificial Consortium Based On Fast-growing Cyanobacterium Synechococcus Elongatus UTEX 2973 To Produce Platform Chemical 3-hydroxypropionic Acid

Cyanobacteria can fix CO₂ directly.In recent years they were also used as"cell factory"for heterologous synthesis of chemicals,cyanobacterial carbohydrates,such as sucrose,which has been considered as a potential renewable feedstock to support the production of fuels and chemicals.However,pure-culture systems of sugar-producing cyanobacteria are very easy to be contaminated,and the separation and purification processes of these carbohydrates will increase the production cost of chemicals.It has been proposed that co-culture fermentation could be an efficient and economical way to utilize these cyanobacterial carbohydrates.In this study,we successfully achieved one-step conversion of CO₂ fixed by cyanobacteria to fine chemicals by constructing a microbial consortium consisted of fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 and Escherichia coli to sequentially produce sucrose and then platform chemical 3-hydroxypropionic acid(3-HP)from CO₂ under photoautotrophic growth condition.First,efforts were made to overexpress sucrose permease coding gene csc B under strong promoter P_cpc560in S.elongatus UTEX 2973 for efficient sucrose secretion.Second,sucrose catabolic pathway and malonyl Co A-dependent 3-HP biosynthetic pathway were introduced into E.coli BL21(DE3)for heterologous biosynthesis of 3-HP from sucrose.By optimizing the cultivation temperature from 37?to 30?,a stable artificial consortium system was constructed with the capability of producing 3-HP up to 68.29 mg/L directly from CO₂.In addition,we found that cyanobacteria grew better in consortium than the axenic culture,so we further explored the interaction mechanism between different members,and the results showed that it is probably due to the quenching of reactive oxygen species(ROS)in the system by E.coli,which in turn improved photosynthesis of cyanobacteria.The study demonstrated the feasibility of achieving the one-step conversion of CO₂ to fine chemicals using an artificial consortium system.The study also confirmed that the heterotrophic bacteria could promote cell growth of cyanobacteria by relieving oxidative stress in this microbial consortium,which further suggests the potential values of the co-culture systems for the future industrial application.