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Main Title: Functional exploration of co-expression networks identifies a nexus for modulating protein and citric acid titres in Aspergillus niger submerged culture
Author(s): Cairns, Timothy C.
Feurstein, Claudia
Zheng, Xiaomei
Zhang, Li Hui
Zheng, Ping
Sun, Jibin
Meyer, Vera
Type: Article
Language Code: en
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.
Issue Date: 9-Nov-2019
Date Available: 14-Feb-2020
DDC Class: 630 Landwirtschaft und verwandte Bereiche
Subject(s): protein secretion
citric acid
aspergillus niger
dispersed mycelia
polar growth
genome editing
Sponsor/Funder: TU Berlin, Open-Access-Mittel - 2019
Journal Title: Fungal Biology and Biotechnology
Publisher: BioMed Central
Publisher Place: London
Volume: 6
Article Number: 18
Publisher DOI: 10.1186/s40694-019-0081-x
EISSN: 2054-3085
Appears in Collections:FG Angewandte und Molekulare Mikrobiologie » Publications

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