Optimization of l-malic acid production from acetate with Aspergillus oryzae DSM 1863 using a pH-coupled feeding strategy

Abstract

Background Malic acid, a dicarboxylic acid mainly used in the food industry, is currently produced from fossil resources. The utilization of low-cost substrates derived from biomass could render microbial processes economic. Such feedstocks, like lignocellulosic hydrolysates or condensates of fast pyrolysis, can contain high concentrations of acetic acid. Acetate is a suitable substrate for l-malic acid production with the filamentous fungus Aspergillus oryzae DSM 1863, but concentrations obtained so far are low. An advantage of this carbon source is that it can be used for pH control and simultaneous substrate supply in the form of acetic acid. In this study, we therefore aimed to enhance l-malate production from acetate with A. oryzae by applying a pH-coupled feeding strategy. Results In 2.5-L bioreactor fermentations, several feeding strategies were evaluated. Using a pH-coupled feed consisting of 10 M acetic acid, the malic acid concentration was increased about 5.3-fold compared to the batch process without pH control, resulting in a maximum titer of 29.53 ± 1.82 g/L after 264 h. However, it was not possible to keep both the pH and the substrate concentration constant during this fermentation. By using 10 M acetic acid set to a pH of 4.5, or with the repeated addition of NaOH, the substrate concentration could be maintained within a constant range, but these strategies did not prove beneficial as lower maximum titers and yields were obtained. Since cessation of malic acid production was observed in later fermentation stages despite carbon availability, a possible product inhibition was evaluated in shake flask cultivations. In these experiments, malate and succinate, which is a major by-product during malic acid production, were added at concentrations of up to 50 g/L, and it was found that A. oryzae is capable of organic acid production even at high product concentrations. Conclusions This study demonstrates that a suitable feeding strategy is necessary for efficient malic acid production from acetate. It illustrates the potential of acetate as carbon source for microbial production of the organic acid and provides useful insights which can serve as basis for further optimization.

The characteristics of the novel bacterial strain Pseudomonas mendocina isolated from freshwater aquaculture farm

“…Arginine dihydrolase (ADH) can convert arginine to ornithine, accompanied by the release of carbon dioxide and ammonia, as well as playing a crucial role in nitrogen storage and remobilization [22]. Malic acid (MTE) is a dicarboxylic acid mainly used in the food industry and can be produced by microbial fermentation oxidation/ reduction TCA and glyoxylic acid pathways, as well as from fossil resources [23]. By shaker fermentation, lactose is effectively converted to lactose acid (LAC), which is widely used in the pharmaceutical, food, nanotechnology and chemical industries [24].…”

Two-stage conversion of syngas and pyrolysis aqueous condensate into L-malate

“…When grown in shaking flasks on acetate, A. oryzae yielded up to 21% g L -malate /g acetate but the production was highly dependent upon the initial acetate concentration [ 64 ]. In bioreactor experiments optimized for L-malate production from acetate, A. oryzae produced about 29 g/L L-malate corresponding to a 29% g L -malate /g acetate L-malate yield [ 63 ]. During the cultivation of A. oryzae with acetate and acetol from a detoxified PAC, L-malate was produced up to 7.3 ± 0.3 g/L (corresponding to a yield of 20 ± 0.01 g L -malate /g substrates ) [ 69 ].…”

“…Fungi have been reported to be the microorganisms most tolerant to the oil fraction of the condensates from pyrolysis [56], and the tolerance of Aspergillus oryzae to PAC and some selected PAC components has been characterized before [48,57,58]. A. oryzae is known for its metabolic versatility to grow on sugars and carboxylic acids present in various waste streams for the production of single cell proteins [59][60][61][62] or L-malate [63][64][65], among other chemicals. L-Malate has a wide array of applications, ranging from taste-enhancer in the food industry to biopolymer production [66].…”

Isolation of Pseudomonas oleovorans Carrying Multidrug Resistance Proteins MdtA and MdtB from Wastewater

“…It has been reported that ADH was found in ArgZ from Synechocystis and AgrE from Anabaena , which play crucial roles in nitrogen storage and remobilization [ 31 ]. Malic acid, a dicarboxylic acid mainly used in the food industry, can be produced by microbial fermentation via oxidation/reduction of TCA and glyoxylic acid pathways, and can also be produced from fossil resources [ 32 ]. Lactococcus lactis biovar diacetylactis is one of the main strains that degrade citrate in dairy product starter cultures.…”