Study On Screening,Characterization And Poly Malic Acid Fermentation By Aureobasidium Spp.

Poly malic acid(PMLA)is a kind of high molecular polymer formed by the ester linkage of malate.The unique structure of polymalic acid gives it a wide range of applications in the fields of biomedicine,food industry and cosmetics.The polymalic acid produced by the bio-fermentation method are all β-type,and the monomers are L-malic acid.β-PMLA are more widely used and more suitable for the production of various biological materials.The currently reported the high-yield polymalic acid microorganism are Aureobasidium spp.This paper isolated and screened Aureobasidium spp.strains from nature and through molecular biology methods identified strains.The phylogenetic tree was constructed.The effect of dissolved oxygen on the fermentation yield of Aureobasidium pullulans was explored and the main metabolic pathway for the synthesis of polymalic acid from Aureobasidium pullulans ipe-1 was explored through metabolic regulation of fermentation.The main findings of this paper are as follows:(1)A total of 18 colonies were obtained on methylene blue medium.After shake flask screening,2 strains producing poly malic acid were found,which named ipe-3 and ipe-5.Through molecular biology identification,ipe-3 was Aureobasidium pullulans,ipe-5 was Aureobasidium sp.The ITS sequences of ipe-3 and ipe-5 were submitted to GenBank database.ipe-5 was the first reported Aureobasidium sp.strain which had only 96% homology with the known ITS sequence in GenBank database.(2)The fermentation performance of ipe-3 and ipe-5 were tested.The results showed that the poly malic acid yield of ipe-3 was 10.027 g/L,the malic acid yield was 5.70 g/L,as for ipe-5 the poly malic acid yield was 0.3 g/L and the malic acid yield was 57.24 g/L.Ipe-5 has the characteristics of short fermentation time and high production intensity.The production strength of malic acid can reach 1.19 g/L· h.(3)The effect of dissolved oxygen on the yield of poly malic acid showed that when the dissolved oxygen concentration decreased from 70% to 10%,the poly malic acid yield of ipe-3 decreased by 41.67%.The main fermentation product malic acid of ipe-5 decreased by 83.05%.The yield of poly malic acid of ipe-1 was reduced by 54.44%.(4)Through enzyme activity analyze,the sugar-metabolize pathway of ipe-1 contained pentose phosphate pathway,glycolytic pathway and TCA cycle.Pentose phosphate pathway played an important role in PMLA synthesis.Through metabolic regulation found that phosphoenolpyruvate carboxylase catalyzed to oxaloacetate pathway were the key pathway for the synthesis of poly malic acid where required the participation of ATP.