Differential Analysis of Key Genes Involved in the Accumulation of L-malic Acid by Aspergillus niger Fermentation
[Objective]Microbial production of L-malic acid is currently an extremely efficient producing method.In order to reveal the biosynthetic mechanism of L-malic acid production by Aspergillus niger,the differential changes of key genes in the metabolic regulation process were explored with the help of transcriptomic analysis.[Method]The acid production level of MA-1 strain reached 88.27 g/L at 144 h of fermentation,and three time points(48,72,and 120 h)with different acid production rates were selected for transcriptome analysis.[Result]GO analysis showed that the regulation of biological processes,RNA binding and ribosome-related secondary entries under the significant genes were the most differentiated and the largest number.Transcriptome analysis revealed that transcriptional regulators such as HacA,Ace1,and Rpn4 were consistently at high levels during fermentation from 48 to 120 h,with FPKM values reaching 20 181.64-94 573.00,and that glucose transporter protein(Rco-3),and ketoglutarate/malate transporter protein Yhm1 showed relatively high transcript levels,with FPKM values reaching 4 971.83-6 575.46;in the glycolytic EMP pathway,its important rate-limiting enzyme pyruvate kinase(FPKM values of 13 109.15-25 649.30)and ANI_1_1984024 among the six hexokinase enzymes(FPKM values up to 4 111.68-7 325.43)showed relatively high transcript levels,and then the pathway for the conversion from glucose to pyruvate.The transcript levels of other enzymes in the glucose-to-pyruvate pathway showed a decreasing trend at 120 h.The transcript levels of the whole genes in the TCA cycle were maintained at a high level to provide sufficient energy for cellular metabolism,and the highest level of citrate synthase in the rTCA pathway,followed by malate dehydrogenase,and the level of the glyoxylate cycle was low.[Conclusion]The main pathways of L-malate synthesis in A.niger MA-1 strain were presumed to be rTCA and pyruvate carboxylation pathway.
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