Engineering Escherichia coli for efficient aerobic conversion of glucose to fumaric acid

A comprehensive review on the recent advances for 5-aminolevulinic acid production by the engineered bacteria

5-Aminolevulinic acid (5-ALA) is a non-proteinogenic amino acid essential for synthesizing tetrapyrrole compounds, including heme, chlorophyll, cytochrome, and vitamin B12. As a plant growth regulator, 5-ALA is extensively used in agriculture to enhance crop yield and quality. The complexity and low yield of chemical synthesis methods have led to significant interest in the microbial synthesis of 5-ALA. Advanced strategies, including the: enhancement of precursor and cofactor supply, compartmentalization of key enzymes, product transporters engineering, by-product formation reduction, and biosensor-based dynamic regulation, have been implemented in bacteria for 5-ALA production, significantly advancing its industrialization. This article offers a comprehensive review of recent developments in 5-ALA production using engineered bacteria and presents new insights to propel the field forward.

Engineering Escherichia coli for Efficient Aerobic Conversion of Glucose to Malic Acid through the Modified Oxidative TCA Cycle

Malic acid is a versatile building-block chemical that can serve as a precursor of numerous valuable products, including food additives, pharmaceuticals, and biodegradable plastics. Despite the present petrochemical synthesis, malic acid, being an intermediate of the TCA cycle of a variety of living organisms, can also be produced from renewable carbon sources using wild-type and engineered microbial strains. In the current study, Escherichia coli was engineered for efficient aerobic conversion of glucose to malic acid through the modified oxidative TCA cycle resembling that of myco- and cyanobacteria and implying channelling of 2-ketoglutarate towards succinic acid via succinate semialdehyde formation. The formation of succinate semialdehyde was enabled in the core strain MAL 0 (∆ackA-pta, ∆poxB, ∆ldhA, ∆adhE, ∆ptsG, PL-glk, Ptac-galP, ∆aceBAK, ∆glcB) by the expression of Mycobacterium tuberculosis kgd gene. The secretion of malic acid by the strain was ensured, resulting from the deletion of the mdh, maeA, maeB, and mqo genes. The Bacillus subtilis pycA gene was expressed in the strain to allow pyruvate to oxaloacetate conversion. The corresponding recombinant was able to synthesise malic acid from glucose aerobically with a yield of 0.65 mol/mol. The yield was improved by the derepression in the strain of the electron transfer chain and succinate dehydrogenase due to the enforcement of ATP hydrolysis and reached 0.94 mol/mol, amounting to 94% of the theoretical maximum. The implemented strategy offers the potential for the development of highly efficient strains and processes of bio-based malic acid production.

The important role of tricarboxylic acid cycle metabolism pathways and core bacterial communities in carbon sequestration during chicken manure composting

As a kind of livestock manure, chicken manure (CM) was rich in organic matter and microorganisms. However, a large amount of foul gas discharged by its random stacking not only threatened the environment, but also caused harm to human health. In view of the serious carbon loss and the unclear action mechanism of microbial community on carbon metabolism during CM composting, the effect of adding regulators on the sequestration of organic carbon was explored. Therefore, the purpose of this study was to explore the regulation mechanism of adding tricarboxylic acid cycle (TCA cycle) regulators on the core carbon metabolism pathway during CM composting. The results showed that the adenosine triphosphate (ATP) and malonic acid (MA) slowed down organic carbon degradation, resulting in lower carbon loss rate, which were 64.99% (CK), 62.35% (MA), and 61.26% (ATP) in each treatment. By comparing the abundance and structure of the carbon-related bacterial communities in different treatments, it was found that adding ATP and MA not only reduced the bacterial community abundance, but also tended to be similar in bacterial community composition. Moreover, the microbial specificity related to carbon metabolism pathway was enhanced, while the related gene expression and gene abundance were weakened. The regulation of TCA cycle metabolism pathway was confirmed to be the main way to improve organic carbon content. These findings revealed the positive effects of ATP and MA on carbon fixation from the perspective of gene metabolism.