Comprehensively dissecting the hub regulation of PkaC on high‐productivity and pellet macromorphology in citric acid producing Aspergillus niger

Abstract

Summary Aspergillus niger, an important industrial workhorse for citric acid production, is characterized by polar hyphal growth with complex pelleted, clumped or dispersed macromorphologies in submerged culture. Although organic acid titres are dramatically impacted by these growth types, studies that assess productivity and macromorphological changes are limited. Herein, we functionally analysed the role of the protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP) signalling cascade during fermentation by disrupting and conditionally expressing the pkaC gene. pkaC played multiple roles during hyphal, colony and conidiophore growth. By overexpressing pkaC, we could concomitantly modify hyphal growth at the pellet surface and improve citric acid titres up to 1.87‐fold. By quantitatively analysing hundreds of pellets during pilot fermentation experiments, we provide the first comprehensive correlation between A. niger pellet surface morphology and citric acid production. Finally, by intracellular metabolomics analysis and weighted gene coexpression network analysis (WGCNA) following titration of pkaC expression, we unveil the metabolomic and transcriptomic basis underpin hyperproductivity and pellet growth. Taken together, this study confirms pkaC as hub regulator linking submerged macromorphology and citric acid production and provides high‐priority genetic leads for future strain engineering programmes.

Evaluation of Aspergillus niger Six Constitutive Strong Promoters by Fluorescent-Auxotrophic Selection Coupled with Flow Cytometry: A Case for Citric Acid Production

“…The samples for transcriptomic profiling were prepared and detected according to a previous approach [ 35 ]. Briefly, the mycelial samples were collected by rapid vacuum filtration after cultivating for 72 h in a 5 L bioreactor, washed with 100 mL cold sterilized water, and then immediately placed into liquid nitrogen and stored at −80 °C.…”

Recent Advances in Chitin Biosynthesis Associated with the Morphology and Secondary Metabolite Synthesis of Filamentous Fungi in Submerged Fermentation

“…Often, it is not clear which morphological form is the most suitable for the efficient production of a given metabolite or enzyme. Dense mycelial pellets, within an appropriate range of diameters, are a favorable morphology for the biosynthesis of citric acid by Aspergillus niger [ 13 , 18 , 19 ], whereas, in Aspergillus oryzae , mycelium comprising numerous hyphal tips is more conducive to the production of enzymes, such as α-amylase and lipase [ 20 , 21 , 22 ]. Furthermore, the dispersed mycelium of Penicillium chrysogenum is generally regarded as a prerequisite to ensure the high productivity of penicillin in submerged fermentation [ 23 ].…”

“…Furthermore, based on the integrated control of operational parameters (agitation speed and aeration rate) and overexpression of tyrosine-protein phosphatase, Chen et al fine-tuned the morphology of A. oryzae to obtain a more compact pellet structure, and larger pellet number, than the original mycelial morphology in submerged fermentation, thereby increasing the production of l -malate to 142.5 g/L in a 30-L bioreactor [ 87 ]. Moreover, the pka C gene has multiple regulatory effects associated with hyphal growth, and the overexpression of this gene modified the mycelial pellet morphology of A. niger during submerged fermentation, thus contributing to a 1.87-fold increase in the concentration of citric acid [ 19 ]. More recently, microparticle-enhanced cultivation techniques have been successfully applied in the submerged fermentation cultivation of different fungal genera.…”

One-step co-cultivation and flocculation of microalgae with filamentous fungi to valorize starch wastewater into high-value biomass

“…Algal cells co-cultured with A. oryzae kept green and alive even been completely encapsulated and the solution was clear after 3 days culture (see supplementary material). A. niger is an important organic acid producing strain and high concentration organic acid was gradually accumulated in the suspension during the culture of A. niger (Zheng et al, 2022b). Meanwhile, the pH of the suspension gradually decreased and dropped below 4.0 in co-cultures with A. niger after 3 days culture.…”