Co-consumption of glucose and xylose for organic acid production by Aspergillus carbonarius cultivated in wheat straw hydrolysate

Abstract

Aspergillus carbonarius exhibits excellent abilities to utilize a wide range of carbon sources and to produce various organic acids. In this study, wheat straw hydrolysate containing high concentrations of glucose and xylose was used for organic acid production by A. carbonarius. The results indicated that A. carbonarius efficiently co-consumed glucose and xylose and produced various types of organic acids in hydrolysate adjusted to pH 7. The inhibitor tolerance of A. carbonarius to the hydrolysate at different pH values was investigated and compared using spores and recycled mycelia. This comparison showed a slight difference in the inhibitor tolerance of the spores and the recycled mycelia based on their growth patterns. Moreover, the wild-type and a glucose oxidase deficient (Δgox) mutant were compared for their abilities to produce organic acids using the hydrolysate and a defined medium. The two strains showed a different pattern of organic acid production in the hydrolysate where the Δgox mutant produced more oxalic acid but less citric acid than the wild-type, which was different from the results obtained in the defined medium This study demonstrates the feasibility of using lignocellulosic biomass for the organic acid production by A. carbonarius.

Overexpression of a C4-dicarboxylate transporter is the key for rerouting citric acid to C4-dicarboxylic acid production in Aspergillus carbonarius

“…In the hydrolysate, the sugar consumption by all the strains began later than that observed in the defined medium. The inhibitory effects on spore germination and fungal growth in the hydrolysate which delayed sugar consumption in the first two days have been reported in our previous study [15]. However, inoculating with fungal mycelia from pre-culture in this study did not improve the inhibitor tolerance or accelerate the sugar consumption in the early phase of cultivation.…”

“…Carbohydrates existing in lignocellulosic biomass are considered as cheap alternative substrates for organic acid production [6]. A. carbonarius has been reported for its efficient co-utilization of glucose and xylose during the cultivation and its ability to produce different types of organic acids from the hydrolysate such as citric acid and gluconic acid [15]. In this study, we have further demonstrated its ability to produce C 4 -dicarboxylic acids from lignocellulosic biomass with the developed strains.…”

“…The defined medium consisted of glucose, 80 g/L; NH 4 NO 3 , 1.5 g/L; KH 2 PO 4 , 0.15 g/L; MgSO 4 ·7H 2 O, 0.8 g/L; CaCl 2 ·2H 2 O, 0.2 g/L; NaCl, 0.15 g/L; ZnSO 4 , 0.0015 g/L; FeSO 4 ·7H 2 O, 0.03 g/L; biotin, 1 × 10 −5 g/L and CaCO 3 , 80 g/L [26]. The liquid fraction of the wheat straw hydrolysate was prepared as previously described and supplemented with the same amounts of nutrients (except glucose and xylose) and calcium carbonate as mentioned in the defined medium [15]. The pH of hydrolysate was adjusted to 6.5 using 10 M NaOH followed by sterilization with 0.2 µm sterile filter (Nalgene ® ).…”

“…Aspergillus carbonarius , a member of black aspergilli, possesses several valuable virtues to be a competent cell factory for organic acid production. It can produce different types of organic acids (citric acid, gluconic acid and malic acid) from varieties of substrates ranging from mono-sugars to polysaccharides such as glucose, xylose, cellulose and starch, and tolerate stress conditions, especially low pH, during organic acid production [14, 15]. Organic acid profiling of A. carbonarius has shown its capability of producing high amounts of citric acid and gluconic acid under different pH conditions [16].…”

Metabolic engineering of Aspergillus niger via ribonucleoprotein-based CRISPR–Cas9 system for succinic acid production from renewable biomass

“…Compared with the defined medium, a significant inhibitory effect was observed only in the wheat straw hydrolysate but not in the culture containing molasses. Our previous study has shown that a number of inhibitors, especially acetic acid, in the hydrolysate can suppress the spore germination and mycelial growth in the early stage of the fungal cultivation [44]. Normally these inhibitors are converted in the lag phase before sugar consumption begin, which is consistent with the phenomenon that the acetic acid consumption preceded sugar consumption in the wheat straw hydrolysate in this study.…”