Abstract
Dissolved oxygen (DO) is an important factor in the fermentation process of Corynebacterium glutamicum, which is a widely used aerobic microbe in bio-industry. Herein, we described RNA-seq for C. glutamicum under different DO levels (50%, 30% and 0%) in 5 L bioreactors. Multivariate data analysis (MVDA) models were used to analyze the RNA-seq and metabolism data to investigate the global effect of DO on the transcriptional distinction of the substance and energy metabolism of C. glutamicum. The results showed that there were 39 and 236 differentially expressed genes (DEGs) under the 50% and 0% DO conditions, respectively, compared to the 30% DO condition. Key genes and pathways affected by DO were analyzed, and the result of the MVDA and RNA-seq revealed that different DO levels in the fermenter had large effects on the substance and energy metabolism and cellular redox balance of C. glutamicum. At low DO, the glycolysis pathway was up-regulated, and TCA was shunted by the up-regulation of the glyoxylate pathway and over-production of amino acids, including valine, cysteine and arginine. Due to the lack of electron-acceptor oxygen, 7 genes related to the electron transfer chain were changed, causing changes in the intracellular ATP content at 0% and 30% DO. The metabolic flux was changed to rebalance the cellular redox. This study applied deep sequencing to identify a wealth of genes and pathways that changed under different DO conditions and provided an overall comprehensive view of the metabolism of C. glutamicum. The results provide potential ways to improve the oxygen tolerance of C. glutamicum and to modify the metabolic flux for amino acid production and heterologous protein expression.
Highlights
Corynebacterium glutamicum (C. glutamicum) has played a principal role in the progress of the amino acid, organic acid and other bulk chemical fermentation industry [1,2,3]
Previous research demonstrated that the glycolysis and TCA cycle under oxygen deprivation is controlled in part by the intracellular NAD+/NADH ratio in C. glutamicum [31]
The rate of NAD+/ NADH at 0% Dissolved oxygen (DO) is much lower than 30% DO and 50% DO, and the transcriptome profiling analysis and metabolism analysis at 0% DO produced consistent results (Fig 8): NCgl0603 and NCgl0328 were down-regulated and the ETC was restricted by oxygen limitation
Summary
Corynebacterium glutamicum (C. glutamicum) has played a principal role in the progress of the amino acid, organic acid and other bulk chemical fermentation industry [1,2,3] It is a Grampositive bacteria with high G+C content chromosomal DNA and the capability to produce a variety of commercially useful chemicals and materials [4,5,6]. Dissolved oxygen (DO) is an important factor that significantly influences metabolism, biomass synthesis, electron transport, ATP availability, peptide folding, and product yield of C. glutamicum when it expresses recombinant protein in a bioreactor [1, 14, 15], due to the complexity of the relationship between oxygen supplementation and fermentation production, increasing the DO level does not guarantee increased yield [15]. To further understand the relationship between substance and energy metabolism in complex bioprocesses, we analyzed the variation of substance and energy metabolism in C. glutamicum under different DO levels
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