Carbon Source For Microbial Production Research Articles

Synthesis of isobutanol using acetate as sole carbon source in Escherichia coli

BackgroundWith concerns about depletion of fossil fuel and environmental pollution, synthesis of biofuels such as isobutanol from low-cost substrate by microbial cell factories has attracted more and more attention. As one of the most promising carbon sources instead of food resources, acetate can be utilized by versatile microbes and converted into numerous valuable chemicals.ResultsAn isobutanol synthetic pathway using acetate as sole carbon source was constructed in E. coli. Pyruvate was designed to be generated via acetyl-CoA by pyruvate-ferredoxin oxidoreductase YdbK or anaplerotic pathway. Overexpression of transhydrogenase and NAD kinase increased the isobutanol titer of recombinant E. coli from 121.21 mg/L to 131.5 mg/L under batch cultivation. Further optimization of acetate supplement concentration achieved 157.05 mg/L isobutanol accumulation in WY002, representing the highest isobutanol titer by using acetate as sole carbon source.ConclusionsThe utilization of acetate as carbon source for microbial production of valuable chemicals such as isobutanol could reduce the consumption of food-based substrates and save production cost. Engineering strategies applied in this study will provide a useful reference for microbial production of pyruvate derived chemical compounds from acetate.

A zero-waste approach towards a sustainable waste management of apple: Extraction of value-added products and their application as edible coating

This study aimed to valorize apple pomace (AP) for the production of value-added products in a zero-waste system. A Box-Behnken design was used to optimize the microwave-assistant extraction factors on simultaneous extraction of pectin (APP) and phenolic compounds (APPC). Under optimum conditions (microwave power of 600 W, irradiation time of 6 min, liquid/solid ratio of 45, and pH of 1.5), the APP and APPC yields were 28.37 ± 1.19% and 3.42 ± 0.48%, respectively. The solid residue after co-extraction was used as a carbon source for microbial production of pullulan and single cell protein (SCP) and the maximum production yields of pullulan (43.7 g/L) and SCP (33.5%) were gained after sequential homogenization, ultrasonication and enzymatic treatment (H + U + E). The molecular weight of APP and pullulan were found to be 690.293 and 366.246 kDa, respectively. Also, the FT-IR and 1H NMR analysis confirmed the presence of pectin and pullulan in the resulting sample and their XRD pattern showed an amorphous structure. The results of DPPH, ABTS and FRAP assays indicated that the antioxidant capacity of apple pomace phenolics was comparable with vitamin C and BHA at high concentrations. Moreover, the coating with 50:50 ratios of APP and pullulan enriched with 15% APPC was selected as the best edible coating for strawberry that prolonged its shelf life until 24 days at 4 °C. The outcomes revealed that the extraction of these valuable compounds from AP in line with the sustainable agriculture development not only reduces environmental problems, but also the obtained products can be used to coat fruits.

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

BackgroundMalic 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.ResultsIn 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.ConclusionsThis 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.

Aerobic Utilization of Methanol for Microbial Growth and Production.

Methanol is a reduced one-carbon (C1) compound. It supports growth of aerobic methylotrophs that gain ATP from reduced redox equivalents by respiratory phosphorylation in their electron transport chains. Notably, linear oxidation of methanol to carbon dioxide may yield three reduced redox equivalents if methanol oxidation is NAD-dependent as, e.g., in Bacillus methanolicus. Methanol has a higher degree of reduction per carbon than glucose (6 vs. 4), and thus, lends itself as an ideal carbon source for microbial production of reduced target compounds. However, C-C bond formation in the RuMP or serine cycle, a prerequisite for production of larger molecules, requires ATP and/or reduced redox equivalents. Moreover, heat dissipation and a high demand for oxygen during catabolic oxidation of methanol may pose challenges for fermentation processes. In this chapter, we summarize metabolic pathways for aerobic methanol utilization, aerobic methylotrophs as industrial production hosts, strain engineering, and methanol bioreactor processes. In addition, we provide technological and market outlooks.