Study On Polymalic Acid Production From Aureobasidium Pullulans ATCC201428

Polymalic acid（PMLA） is an unbranched polymer consisting of monomeric units ofL-malic acid，which has many wonderful properties such as water-soluble and biodegradable，and can be easily modified because of its chemical structure．As a promising biomaterial，PMLA has attracted many industrial interests，especially in biomedical field．But the lowproductivity and high cost of biosynthesis limited the application，thus it is necessary to beimproved.Firstly, the effects of many factors including glucose concentration, carbon substrate,nitrogen source, pH, metal irons, CaCO₃.on the production of PMLA were investigated, Theresults showed that A.pullulans can utilize a variety of carbon sources to produce PMLA, andsucrose was the best on for PMLA production; The strain can absorb both organic andinorganic nitrogen sources, while the inorganic nitrogen sources can improve PMLAsynthesis.The addition of succinic acid, CaCO₃（1%） and low concentration of Mg²⁺alsoenhanced the PMLA production. By response surface methodology, the fermentation mediumwas optimized as follows: sucrose93.2g/L, sodium nitrate2.4g/L, succinic acid3.4g/L,MgSO₄7H₂O0.1mmol/L, KH₂PO₄0.1g/L, KCl0.5g/L, CaCO₃10g/L. The theoreticalPMLA yield is9.08g/L, while the experimental PMLA concentration was8.94g/L, which wasimproved by123.5%compared with the original concentration （4g/L）.CPBR has the advantages, such as lower cost, higher steady, higher production and yieldand it is easy to be scaled up comparing with the traditional immobilized fermentation. Tofurther optimize the process, enhance the production and reduce the cost, the feasibility ofusing CPBR for PMLA production was studied as well as the different modes of CPBRfermentation. The feasibility of using CPBR in PLMA production was proved by theinvestigation of the adsorption of the cells. And the result showed that, bacterial cells havegreater adsorption capacity on the fibrous material in the mid-logarithmic growth period, andthe largest amount of cell load on the cotton fiber fabric under this situation was46.0%and27.8%higher than that in the early lag phaseand stationary phase, respectively. The optimalpH was7.0for the adsorption of the cells and the addtionof sucrose （80g/L） or NaNO₃（2.4g/L）enhanced the cell loads on the CPBR.The dilution rate and the sucrose concentration were optimized inthe immobilizedcontinuous fermentation in CPBR for PMLA production. And the best dilution rate (0.10h^-1)and sucrose concentration （20g/L） was obtained for this fermentation mode in CPBR. Comparing with the batch immobilized fermentation in CPBR, free cell batch fermentationand free cell continuous fermentation, the immobilized continuous fermentation using CPBRgave a much higher PMLA productivity （increased by183%,400%and40%, respectively）,PMLA yield （increasedby132%,144%and70%, respectively） and higher sugarutilization.These results indicated that immobilized continuous fermentation with CPBR canimprove PMLA yield effectively.