Qualitative and Quantitative Analysis of Organic Acid Production  Influenced by Phosphate Sources under Submerged Culture of  Aspergillus niger a Phosphate Solubilising Fungi

ABSTRACTDuring fungal rock phosphate (RP) solubilization, a significant quantity of fluoride (F−) is released together with phosphorus (P), strongly inhibiting the process. In the present study, the effect of two F−adsorbents [activated alumina (Al2O3) and biochar] on RP solubilization byAspergillus nigerwas examined. Al2O3adsorbed part of the F−released but also adsorbed soluble P, which makes it inappropriate for microbial RP solubilization systems. In contrast, biochar adsorbed only F−while enhancing phosphate solubilization 3-fold, leading to the accumulation of up to 160 mg of P per liter. By comparing the values of F−measured in solution at the end of incubation and those from a predictive model, it was estimated that up to 19 mg of F−per liter can be removed from solution by biochar when added at 3 g liter−1to the culture medium. Thus, biochar acted as an F−sink during RP solubilization and led to an F−concentration in solution that was less inhibitory to the process. In the presence of biochar,A. nigerproduced larger amounts of citric, gluconic, and oxalic acids, whether RP was present or not. Our results show that biochar enhances RP solubilization through two interrelated processes: partial removal of the released F−and increased organic acid production. Given the importance of organic acids for P solubilization and that most of the RPs contain high concentrations of F−, the proposed solubilization system offers an important technological improvement for the microbial production of soluble P fertilizers from RP.

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Functional exploration of co-expression networks identifies a nexus for modulating protein and citric acid titres in Aspergillus niger submerged culture

Fungal Biology and Biotechnology ◽

10.1186/s40694-019-0081-x ◽

2019 ◽

Vol 6 (1) ◽

Cited By ~ 6

Author(s):

Timothy C. Cairns ◽

Claudia Feurstein ◽

Xiaomei Zheng ◽

Li Hui Zhang ◽

Ping Zheng ◽

...

Keyword(s):

Citric Acid ◽

Aspergillus Niger ◽

Organic Acid ◽

Protein Secretion ◽

Acid Production ◽

Citric Acid Cycle ◽

Filamentous Growth ◽

Growth Media ◽

Organic Acid Production ◽

Acid Cycle

Abstract Background Filamentous fungal cell factories are used to produce numerous proteins, enzymes, and organic acids. Protein secretion and filamentous growth are tightly coupled at the hyphal tip. Additionally, both these processes require ATP and amino acid precursors derived from the citric acid cycle. Despite this interconnection of organic acid production and protein secretion/filamentous growth, few studies in fungi have identified genes which may concomitantly impact all three processes. Results We applied a novel screen of a global co-expression network in the cell factory Aspergillus niger to identify candidate genes which may concomitantly impact macromorphology, and protein/organic acid fermentation. This identified genes predicted to encode the Golgi localized ArfA GTPase activating protein (GAP, AgeB), and ArfA guanine nucleotide exchange factors (GEFs SecG and GeaB) to be co-expressed with citric acid cycle genes. Consequently, we used CRISPR-based genome editing to place the titratable Tet-on expression system upstream of ageB, secG, and geaB in A. niger. Functional analysis revealed that ageB and geaB are essential whereas secG was dispensable for early filamentous growth. Next, gene expression was titrated during submerged cultivations under conditions for either protein or organic acid production. ArfA regulators played varied and culture-dependent roles on pellet formation. Notably, ageB or geaB expression levels had major impacts on protein secretion, whereas secG was dispensable. In contrast, reduced expression of each predicted ArfA regulator resulted in an absence of citric acid in growth media. Finally, titrated expression of either GEFs resulted in an increase in oxaloacetic acid concentrations in supernatants. Conclusion Our data suggest that the Golgi may play an underappreciated role in modulating organic acid titres during industrial applications, and that this is SecG, GeaB and AgeB dependent in A. niger. These data may lead to novel avenues for strain optimization in filamentous fungi for improved protein and organic acid titres.

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