Abstract
BackgroundIn general, high-quality seed is the prerequisite of an efficient bioprocess. However, in terms of sodium gluconate production by Aspergillus niger, reports have seldom focused on seed culture with rational optimization by process analysis technology, especially for carbon source effects. In this study, based on the online physiological parameter of oxygen uptake rate (OUR), and intracellular metabolite profiling, as well as cell morphology analysis, the effects of different initial glucose concentrations on seed culture by A. niger were investigated.ResultsThe optimum initial glucose concentration was 300 g/L, corresponding to 1900 mOsm/kg, with OUR level about 70% higher than other conditions. Besides, the cells from optimized seed culture accumulated more osmoprotectants of alanine and glutamate. Interestingly, high glucose concentration could induce glucose oxidase (GOD) activity possibly by affecting the synthesis of histidine, one key component of active site of GOD. Prominently, the fermentation yield using the optimized seed culture was up to 1.198 g/g, 99% of the theoretical value, which was the best in literature.ConclusionThe initial glucose concentration appropriately 300 g/L in seed cultivation was determined to be the most optimal. Further, this study would be helpful for guiding sodium gluconate production on industrial scale.
Highlights
High-quality seed is the prerequisite of an efficient bioprocess
Under extreme conditions of group A and group E under 100 and 500 glucose in seed culture (g/L) glucose concentrations in seed culture, corresponding to the initial osmotic pressures of 600 and 3200 mOsm/kg, respectively, the pool sizes of amino acids like glycine (Gly), lysine (Lys), valine (Val), methionine (Met), and threonine (Thr), and central carbon metabolism intermediates such as pyruvic acid (Pyr), 3-phosphogluconic acid (3PG), glyceraldehyde 3-phosphate (G3P), FBP, α-ketoglutarate, malate, succinate (Suc), and fumaric acid (Fum) were 2–3 times of those under 200, 300, and 400 g/L of glucose conditions, corresponding to 1200, 2500, and 2500 mOsm/kg osmotic pressures, respectively. These results suggested that extreme conditions could accelerate more energy to synthesize a series of proteins or enzymes for the better cell growth and metabolism, while the EMP pathway and Effects of initial glucose concentration on mycelium morphology in seed culture by A. niger The macroscopic environment determined microscopic morphology of cells, in turn, the latter of which acted on the mixing and mass transfer through the change of the rheological properties of the broth, affecting the biosynthesis of products
The results showed that the role of glucose as an osmotic regulator was dominant under 250–350 g/L glucose concentrations, which made the research of optimized initial glucose concentration in the seed culture stage more significant
Summary
In terms of sodium gluconate production by Aspergillus niger, reports have seldom focused on seed culture with rational optimization by process analysis technology, especially for carbon source effects. In this study, based on the online physiological parameter of oxygen uptake rate (OUR), and intracellular metabolite profiling, as well as cell morphology analysis, the effects of different initial glucose concentrations on seed culture by A. niger were investigated. During the process of sodium gluconate fermentation by A. niger, batch fermentation is generally adopted for commercial production. As one of the key substrates in sodium gluconate fermentation, has a dual role of providing the required carbon source and increasing the environmental osmotic pressure. Kulandaivel (2014) optimized the gluconic acid production by A. niger by setting three different gradients of glucose concentration and other factors in continuous shaking flask.
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