Comparative evaluation of Aspergillus niger strains for endogenous pectin-depolymerization capacity and suitability for d-galacturonic acid production

Abstract

Pectinaceous agricultural residues rich in d-galacturonic acid (d-GalA), such as sugar beet pulp, are considered as promising feedstocks for waste-to-value conversions. Aspergillus niger is known for its strong pectinolytic activity. However, while specialized strains for production of citric acid or proteins are well characterized, this is not the case for the production of pectinases. We, therefore, systematically compared the pectinolytic capabilities of six A. niger strains (ATCC 1015, ATCC 11414, NRRL 3122, CBS 513.88, NRRL 3, and N402) using controlled batch cultivations in stirred-tank bioreactors. A. niger ATCC 11414 showed the highest polygalacturonase activity, specific protein secretion, and a suitable morphology. Furthermore, d-GalA release from sugar beet pulp was 75% higher compared to the standard lab strain A. niger N402. Our study, therefore, presents a robust initial strain selection to guide future process improvement of d-GalA production from agricultural residues and identifies a high-performance base strain for further genetic optimizations.

Genetic Characterization of Mutations Related to Conidiophore Stalk Length Development in Aspergillus niger Laboratory Strain N402

“…This analysis also included a comparison between N400 and N402. The results indicated that the growth profile in bioreactor was similar, although the N402 strain reached a higher maximum dry biomass level compared to N400 (2.28 ± 0.12 g/L for N400 vs 3.38 ± 0.07 g/L for N402) (Schäfer et al, 2020). The morphology of the mycelium of the N400 and N402 strains during cultivation on pectin was also examined and compared.…”

“…An important consideration is to which extent the mutations in the kinesin-like protein and the transcription factor that lead to shorter conidiophore stalk and reduced radial growth identified in this study might affect the conclusions reached in previous studies. Schäfer et al (2020) performed a comparative study in which different A. niger strains were compared for growth under controlled conditions. This analysis also included a comparison between N400 and N402.…”

“…The total pectinase and endo-specific polygalacturonase activity of medium samples was also analyzed. Compared to N400, the N402 strain had both reduced total pectinase and endo-polygalacturonase activity (Schäfer et al, 2020). A possible role for the cspA or cspB mutations in regulating pectinase expression was also suggested by the reduced expression of plyA [pectate lyase A and pelA (pectin lyase A)] in N400 compared to N402 derivatives (Parenicova, 2000).…”

“…Studies using A. niger as a model investigating transcriptional regulation of (biopolymer degrading) enzyme production are also numerous (e.g., van Peij et al, 1998;Yuan et al, 2008;de Souza et al, 2011;Delmas et al, 2012;Kowalczyk et al, 2015;Alazi et al, 2016). Based on the observation that the expression of pectinases might be altered in the N402 strain (Parenicova, 2000;Schäfer et al, 2020), mutations in N402 might also have an effect on the expression of these enzymes network. To circumvent possible effects of the mutations introduced in N402, N400 should be considered as a true wild-type strain and used preferably.…”

D-Galacturonic acid reduction by S. cerevisiae for L-galactonate production from extracted sugar beet press pulp hydrolysate

“…No growth, no sorbitol consumption, no D-GalA consumption, and no L-GalOA production were observed with S. cerevisiae SiHY001 (data not shown). Enzymatic hydrolysis of SBPP had been performed in 100 mM sodium acetate buffer (Schäfer et al 2020). As acetic acid is known to affect the metabolism of S. cerevisiae already at concentrations as low as 3 mM (Sousa et al 2012), growth of S. cerevisiae SiHY001 was studied in miniaturized single-use stirred tank reactors with diverse buffers and buffer concentrations at pH 5.0 in SC medium (sodium acetate, sodium citrate, potassium acetate, and potassium citrate).…”