Establishment And Optimization Of A Four-microorganism Three-step Fermentation Process For Producing Medium-chain-length Polyhydroxyalkanoate From Starch

Polyhydroxyalkanoate(PHA)is a biosynthetic macromolecular fatty acid ester with certain biodegradability and is an environmentally friendly plastic.However,highcost raw materials and a long-term fermentation process limit PHA Development,there are few reports on the synthesis of medium-chain-length polyhydroxyalkanoate(mclPHA).Based on this purpose,this topic was developed to simulate kitchen waste as a substrate to establish a bioprocess synthesis Research on medium-chain-length polyhydroxyalkanoate(mcl-PHA).In this study,a four-microorganism three-step fermentation process was established for producing medium-chain-length polyhydroxyalkanoate(mcl-PHA)from starch.The four microorganism species used in this process are A.niger,S.cerevisiae,A.orientalis,and P.putida-acs KT2440.The first step was performed using A.niger to transform the initial substrate starch into glucose;then,a S.cerevisiaeA.orientalis consortium was constructed to transform glucose to acetic acid;the third step was accomplished using P.putida-acs KT2440 to utilize acetic acid to produce mcl-PHA.Under the optimal conditions,the initial carbon source starch is set to 30 g/L,The starch is gradually hydrolyzed by A.niger to produce glucose,and the maximum glucose concentration is 17.66 g/L(30℃,220 rpm,p H = 7)after 48 hours of fermentation.In the second step,S.cerevisiae and A.orientalis seed solution were inoculated at 1:60,first anaerobic fermentation for 12 h at 190 rpm,then aerobic fermentation for 12 h at 220 rpm,Alternately,continuous fermentation for 48 h,the maximum acetic acid concentration reaches 2.42 g/L.In the third step,take 1 m L of P.putida-acs KT2440 seed liquid into the fermentation broth containing acetic acid from the second step,then ferment for 48 h in shaker at 30℃,220 rpm.The concentration of mcl-PHA synthesized in the cell of P.putida-acs KT2440 was 0.51 g/L.The multi-step fermentation and mcl-PHA production process proposed in this study for the construction of an artificial mixed bacteria system is the first aerobic production of mcl-PHA using starch as the sole carbon source,compared with the production of PHA using domesticated activated sludge with kitchen waste as a substrate The production cycle is only 6 days(144 h),the fermentation cycle is shortened by more than half,and the production efficiency is greatly improved,thus providing a feasible strategy for the use of kitchen waste for mcl-PHA production.