Production of 5-aminolevulinic acid by an Escherichia coli aminolevulinate dehydratase mutant that overproduces Rhodobacter sphaeroides aminolevulinate synthase

Engineering a probiotic strain of Escherichia coli to induce the regression of colorectal cancer through production of 5-aminolevulinic acid

Bacterial vectors can be engineered to generate microscopic living therapeutics to produce and deliver anticancer agents. Escherichia coli Nissle 1917 (Nissle 1917) is a promising candidate with probiotic properties. Here, we used Nissle 1917 to develop a metabolic strategy to produce 5‐aminolevulinic acid (5‐ALA) from glucose as 5‐ALA plays an important role in the photodynamic therapy of cancers. The coexpression of hemA^M and hemL using a low copy‐number plasmid led to remarkable accumulation of 5‐ALA. The downstream pathway of 5‐ALA biosynthesis was inhibited by levulinic acid (LA). Small‐scale cultures of engineered Nissle 1917 produced 300 mg l⁻¹ of 5‐ALA. Recombinant Nissle 1917 was applied to deliver 5‐ALA to colorectal cancer cells, in which it induced the accumulation of antineoplastic protoporphyrin X (PpIX) and specific cytotoxicity towards colorectal cancer cells irradiated with a 630 nm laser. Moreover, this novel combination therapy proved effective in a mouse xenograft model and was not cytotoxic to normal tissues. These findings suggest that Nissle 1917 will serve as a potential carrier to effectively deliver 5‐ALA for cancer therapy.

We combined the biosynthetic and tumor‐targeting features of the probiotic Escherichia coli Nissle 1917 with PDT to deliver 5‐ALA to colorectal cancer cells. E. coli Nissle 1917 was engineered to produce 5‐ALA, and delivered 5‐ALA to colorectal cancer cells to inhibit growth.

Production of 5-aminolevulinic acid from glutamate by overexpressing HemA1 and pgr7 from Arabidopsis thaliana in Escherichia coli

The important metabolic intermediate 5-aminolevulinic acid (ALA) is useful for cancer treatment or plant growth regulation and has consequently received much attention. In this study, we introduced the HemA1 and pgr7 genes from the higher plant Arabidopsis thaliana into recombinant Escherichia coli to overproduce extracellular 5-aminolevulinic acid via the C5 pathway. In the E. coli BL21 (DE3) strain background, the ALA concentration of the strain expressing both HemA1 and pgr7 was the highest and reached 3080.62 mg/L. Among the 7 tested hosts, ALA production was the highest in E. coli Transetta (DE3). In E. coli Transetta GTR/GBP, the expression levels of zwf, gnd, pgl and RhtA were upregulated. Glutamate induced the expression of the GltJ, GltK, GltL and GltS genes that are in involved in glutamate uptake. The recombinant E. coli Transetta GTR/GBP was able to produce 7642 mg/L ALA in modified minimal medium supplemented with 10 g/L glutamate and 15 g/L glucose after 48 h of fermentation at 22 °C. The results provide persuading evidence for the efficient production of ALA from glucose and glutamate in E. coli expressing A. thaliana HemA1 and pgr7. Further optimization of the fermentation process should be done to improve the ALA production to an industrially relevant level.

Engineering of multiple modular pathways for high-yield production of 5-aminolevulinic acid in Escherichia coli

5-aminolevulinic acid (ALA), an important precursor of tetrapyrroles, has various applications in medicine and agriculture fields. Several methods have been adopted to enhance ALA synthesis in our previous studies. In this study, systematic metabolic engineering strategies were implemented to further improve ALA production in Escherichia coli. Firstly, hemA and hemL with different strength of RBS from the artificially constructed mutation libraries were randomly assembled to balance metabolic flux. Then the expression of ALA dehydratase was rationally regulated by replacing promoter with fliCp to weaken ALA catabolism. Besides, the activity of glutamate-1-semialdehyde aminotransferase was increased through strengthening the native biosynthesis pathway of cofactor pyridoxal 5'-phosphate. Moreover, plasmid stability was improved by 21.4% by deleting recA and endA in the recombinant. Finally, stepwise improvements in ALA production were increased to 5.25 g/L with a pH two-stage strategy in a 3-L fermenter. This study proved the importance of metabolic balance in the pathway.

Carbonyl Stress in Bacteria: Causes and Consequences

Pathways of synthesis of the α-reactive carbonyl compound methylglyoxal (MG) in prokaryotes are described in this review. Accumulation of MG leads to development of carbonyl stress. Some pathways of MG formation are similar for both pro- and eukaryotes, but there are reactions specific for prokaryotes, e.g. the methylglyoxal synthase reaction. This reaction and the glyoxalase system constitute an alternative pathway of glucose catabolism - the MG shunt not associated with the synthesis of ATP. In violation of the regulation of metabolism, the cell uses MG shunt as well as other glycolysis shunting pathways and futile cycles enabling stabilization of its energetic status. MG was first examined as a biologically active metabolic factor participating in the formation of phenotypic polymorphism and hyperpersistent potential of bacterial populations. The study of carbonyl stress is interesting for evolutionary biology and can be useful for constructing highly effective producer strains.

Engineering Corynebacterium glutamicum to produce 5-aminolevulinic acid from glucose

BACKGROUND

Corynebacterium glutamicum is generally regarded as a safe microorganism and is used to produce many biochemicals, including L-glutamate. 5-Aminolevulinic acid (ALA) is an L-glutamate derived non-protein amino acid, and is widely applied in fields such as medicine and agriculture.

RESULTS

The products of the gltX, hemA, and hemL genes participate in the synthesis of ALA from L-glutamate. Their annotated C. glutamicum homologs were shown to be functional using heterologous complementation and overexpression techniques. Coexpression of hemA and hemL in native host led to the accumulation of ALA, suggesting the potential of C. glutamicum to produce ALA for research and commercial purposes. To improve ALA production, we constructed recombinant C. glutamicum strains expressing hemA and hemL derived from different organisms. Transcriptome analysis indicated that the dissolved oxygen level and Fe(2+) concentration had major effects on ALA synthesis. The downstream pathway of heme biosynthesis was inhibited using small molecules or introducing genetic modifications. Small-scale flask cultures of engineered C. glutamicum produced 1.79 g/L of ALA.

CONCLUSION

Functional characterization of the key enzymes indicated complex regulation of the heme biosynthetic pathway in C. glutamicum. Systematic analysis and molecular genetic engineering of C. glutamicum may facilitate its development as a system for large-scale synthesis of ALA.

Optimization of the heme biosynthesis pathway for the production of 5-aminolevulinic acid in Escherichia coli

5-Aminolevulinic acid (ALA), the committed intermediate of the heme biosynthesis pathway, shows significant promise for cancer treatment. Here, we identified that in addition to hemA and hemL, hemB, hemD, hemF, hemG and hemH are also the major regulatory targets of the heme biosynthesis pathway. Interestingly, up-regulation of hemD and hemF benefited ALA accumulation whereas overexpression of hemB, hemG and hemH diminished ALA accumulation. Accordingly, by combinatorial overexpression of the hemA, hemL, hemD and hemF with different copy-number plasmids, the titer of ALA was improved to 3.25 g l⁻¹. Furthermore, in combination with transcriptional and enzymatic analysis, we demonstrated that ALA dehydratase (HemB) encoded by hemB is feedback inhibited by the downstream intermediate protoporphyrinogen IX. This work has great potential to be scaled-up for microbial production of ALA and provides new important insights into the regulatory mechanism of the heme biosynthesis pathway.

High-level soluble expression of the hemA gene from Rhodobacter capsulatus and comparative study of its enzymatic properties

The Rhodobacter capsulatus hemA gene, which encodes 5-aminolevulinic acid synthase (ALAS), was expressed in Escherichia coli Rosetta (DE3) and the enzymatic properties of the purified recombinant ALAS (RC-ALAS) were studied. Compared with ALASs encoded by hemA genes from Agrobacterium radiobacter (AR-ALAS) and Rhodobacter sphaeroides (RS-ALAS), the specific activity of RC-ALAS reached 198.2 U/mg, which was about 31.2% and 69.5% higher than those of AR-ALAS (151.1 U/mg) and RS-ALAS (116.9 U/mg), respectively. The optimum pH values and temperatures of the three above mentioned enzymes were all pH 7.5 and 37 °C, respectively. Moreover, RC-ALAS was more sensitive to pH, while the other two were sensitive to temperature. The effects of metals, ethylene diamine tetraacetic acid (EDTA), and sodium dodecyl sulfate (SDS) on the three ALASs were also investigated. The results indicate that they had the same effects on the activities of the three ALASs. SDS and metal ions such as Co(2+), Zn(2+), and Cu(2+) strongly inhibited the activities of the ALASs, while Mn(2+) exerted slight inhibition, and K(+), Ca(2+), Ba(2+), Mg(2+), or EDTA had no significant effect. The specificity constant of succinyl coenzyme A [(kcat/Km)(S-CoA)] of RC-ALAS was 1.4989, which was higher than those of AR-ALAS (0.7456) and RS-ALAS (1.1699), showing its high catalytic efficiency. The fed-batch fermentation was conducted using the recombinant strain containing the R. capsulatus hemA gene, and the yield of 5-aminolevulinic acid (ALA) achieved was 8.8 g/L (67 mmol/L) under the appropriate conditions.

Recent advances in microbial production of δ-aminolevulinic acid and vitamin B12

δ-aminolevulinate (ALA) is an important intermediate involved in tetrapyrrole synthesis (precursor for vitamin B12, chlorophyll and heme) in vivo. It has been widely applied in agriculture and medicine. On account of many disadvantages of its chemical synthesis, microbial production of ALA has been received much attention as an alternative because of less expensive raw materials, low pollution, and high productivity. Vitamin B12, one of ALA derivatives, which plays a vital role in prevention of anaemia has also attracted intensive works. In this review, recent advances on the production of ALA and vitamin B12 with novel approaches such as whole-cell enzyme-transformation and metabolic engineering are described. Furthermore, the direction for future research and perspective are also summarized.