Cloning, expression, and characterization of 5-aminolevulinic acid synthase from Rhodopseudomonas palustris KUGB306

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.

Downregulating of hemB via synthetic antisense RNAs for improving 5-aminolevulinic acid production in Escherichia coli

Aminolevulinic acid (ALA), a type of natural non-protein amino acid, is a key precursor for the biosynthesis of heme, and it has been broadly applied in medicine, agriculture. Several strategies have been applied to enhance ALA synthesis in bacteria. In the present study, we employed synthetic antisense RNAs (asRNAs) of hemB (encodes ALA dehydratase) to weaken metabolic flux of ALA to porphobilinogen (PBG), and investigated their effect on ALA accumulation. For this purpose, we designed and constructed vectors pET28a-hemA-asRNA and pRSFDuet-hemA-asRNA to simultaneously express 5-ALA synthase (ALAS, encoded by hemA) and PTasRNAs (2 inverted repeat DNA sequences sandwiched with the antisense sequence of hemB), selecting the region ranging from - 57 nt upstream to + 139 nt downstream of the start codon of hemB as a target. The qRT-PCR analysis showed that the mRNA levels of hemB were decreased above 50% of the control levels, suggesting that the anti-hemB asRNA was functioning appropriately. ALA accumulation in the hemB weakened strains were 17.6% higher than that obtained using the control strains while accumulating less PBG. These results indicated that asRNAs can be used as a tool for regulating ALA accumulation in E. coli.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02733-8.

N-terminal engineering of glutamyl-tRNA reductase with positive charge arginine to increase 5-aminolevulinic acid biosynthesis

Five-Aminolevulinic acid (ALA), the universal precursor of all tetrapyrroles, has various applications in medicine and agriculture industries. Glutamyl-tRNA reductase (GluTR) as the first key enzyme of C5 pathway is feedback regulated by heme, and its N-terminus plays a critical role on its stability control. Here, the GluTR N-terminus was engineered by inserting different numbers of positively charged lysine and arginine residues. The results confirmed that insertion of lysine or arginine residues (especially one arginine residue) behind Thr2 significantly increased the stability of GluTR. By co-expression of the GluTR variant R1 and the glutamate-1-semialdehyde aminotransferase, ALA production was improved 1.76-fold to 1220 mg/L. The GluTR variant R1 constructed here could be used for engineering the C5 pathway to enhance ALA and other products.

A New Strategy for Production of 5-Aminolevulinic Acid in Recombinant Corynebacterium glutamicum with High Yield

5-Aminolevulinic acid (ALA), a nonprotein amino acid involved in tetrapyrrole synthesis, has been widely applied in agriculture, medicine, and food production. Many engineered metabolic pathways have been constructed; however, the production yields are still low. In this study, several 5-aminolevulinic acid synthases (ALASs) from different sources were evaluated and compared with respect to their ALA production capacities in an engineered Corynebacterium glutamicum CgS1 strain that can accumulate succinyl-coenzyme A (CoA). A codon-optimized ALAS from Rhodobacter capsulatus SB1003 displayed the best potential. Recombinant strain CgS1/pEC-SB produced 7.6 g/liter ALA using a mineral salt medium in a fed-batch fermentation mode. Employing two-stage fermentation, 12.46 g/liter ALA was produced within 17 h, with a productivity of 0.73 g/liter/h, in recombinant C. glutamicum Through overexpression of the heterologous nonspecific ALA exporter RhtA from Escherichia coli, the titer was further increased to 14.7 g/liter. This indicated that strain CgS1/pEC-SB-rhtA holds attractive industrial application potential for the future.

IMPORTANCE

In this study, a two-stage fermentation strategy was used for production of the value-added nonprotein amino acid 5-aminolevulinic acid from glucose and glycine in a generally recognized as safe (GRAS) host,Corynebacterium glutamicum The ALA titer represented the highest in the literature, to our knowledge. This high production capacity, combined with the potential easy downstream processes, made the recombinant strain an attractive candidate for industrial use in the future.

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.