Transketolase (EC 2.2.1.1, TK) is a thiamine diphosphate-dependent enzyme that catalyzes the transfer of a two-carbon hydroxyacetyl unit with reversible C-C bond cleavage and formation. It is widely used in the production of chemicals, drug precursors, and asymmetric synthesis by cascade enzyme catalysis. In this paper, the activity of transketolase TKTA from Escherichia coli K12 on non-phosphorylated substrates was enhanced through site-directed saturation mutation and combined mutation. On this basis, the synthesis of tartaric semialdehyde was explored. The results showed that the optimal reaction temperature and pH of TKTA_M (R358I/H461S/R520Q) were 32 ℃ and 7.0, respectively. The specific activity on d-glyceraldehyde was (6.57±0.14) U/mg, which was 9.25 times higher than that of the wild type ((0.71±0.02) U/mg). Based on the characterization of TKTA_M, tartaric acid semialdehyde was synthesized with 50 mmol/L 5-keto-d-gluconate and 50 mmol/L non-phosphorylated ethanolaldehyde. The final yield of tartaric acid semialdehyde was 3.71 g with a molar conversion rate of 55.34%. Hence, the results may facilitate the preparation of l-(+)-tartaric acid from biomass, and provide an example for transketolase-catalyzed non-phosphorylated substrates.
Escherichia coli/genetics* ; Transketolase/chemistry* ; Tartrates ; Escherichia coli Proteins/genetics*

Shikimic acid (SA) is the key synthetic material for the chemical synthesis of Oseltamivir, which is prescribed as the front-line treatment for serious cases of influenza. Multi-gene expression vector can be used for expressing the plurality of the genes in one plasmid, so it is widely applied to increase the yield of metabolites. In the present study, on the basis of a shikimate kinase genetic defect strain Escherichia coli BL21 (ΔaroL/aroK, DE3), the key enzyme genes aroG, aroB, tktA and aroE of SA pathway were co-expressed and compared systematically by constructing a series of multi-gene expression vectors. The results showed that different gene co-expression combinations (two, three or four genes) or gene orders had different effects on the production of SA. SA production of the recombinant BL21-GBAE reached to 886.38 mg·L(-1), which was 17-fold (P < 0.05) of the parent strain BL21 (ΔaroL/aroK, DE3).
Escherichia coli ; enzymology ; genetics ; metabolism ; Escherichia coli Proteins ; genetics ; metabolism ; Plasmids ; genetics ; metabolism ; Shikimic Acid ; metabolism

Shikimic acid is an intermediate metabolite in the synthesis of aromatic amino acids in Escherichia coli and a synthetic precursor of Tamiflu. The biosynthesis of shikimic acid requires blocking the downstream shikimic acid consuming pathway that leads to inefficient production and cell growth inhibition. In this study, a dynamic molecular switch was constructed by using growth phase-dependent promoters and degrons. This dynamic molecular switch was used to uncouple cell growth from shikimic acid synthesis, resulting in the production of 14.33 g/L shikimic acid after 72 h fermentation. These results show that the dynamic molecular switch could redirect the carbon flux by regulating the abundance of target enzymes, for better production.
Escherichia coli/genetics* ; Escherichia coli Proteins/genetics* ; Industrial Microbiology/methods* ; Metabolic Engineering ; Shikimic Acid/metabolism*

Glucosamine (GlcN), also called amino sugar, is a compound derived from the substitution of a hydroxyl group of glucose molecule with an amino group. GlcN finds a wide-range of applications in health food and pharmaceutical industries. In our previous research, a recombinant Escherichia coli-glms-gnal was constructed for the efficient production of GlcN and N-acetylglucosamine (GlcNAc), the latter can be readily deacetylated to GlcN under mild acidic conditions. However, the results indicated that the titer of GlcN and GlcNAc decreased significantly due to the transportation of GlcN and GlcNAc from the culture broth to the inside of cells. To alleviate or block the transportation process, nagE gene (encoding for the GlcNAc-specific transporter) and manX gene (encoding for the mannose transporter) were knocked out with the Red homologous recombination method, and two engineered strains, E. coli-glms-gna1-delta nagE (with nagE gene deletion) and E. coli-glms-gna1-delta nagE-delta manX (with nagE and manX genes deletion), were successfully constructed. The two strains were cultured in a 7-L fermentor for the production of GlcN and GlcNAc. The maximal GlcN concentration of control strain E. coli-glms-gnal reached 4.06 g/L, and the maximal GlcNAc concentration reached 41.46 g/L. The maximal GlcN and GlcNAc concentration of E. coli-glms-gna1-delta nagE reached 4.38 g/L and 71.80 g/L, respectively, which were 1.08-fold and 1.70-fold of those of E. coli-glms-gnal, respectively. The maximal GlcN and GlcNAc concentration of E. coli-glms-gnal-delta nagE-delta manX reached 4.82 g/L and 118.78 g/L, respectively, which were 1.20-fold and 2.86-fold of those of E. coli-glms-gnal, respectively. These results suggested that the deletion of nagE and manX could significantly increase the extracellular accumulation of GlcN and GlcNAc. The results obtained here maybe useful for the microbial GlcN production in an industrial scale.
Acetylglucosamine ; biosynthesis ; genetics ; Escherichia coli ; genetics ; metabolism ; Escherichia coli Proteins ; genetics ; Gene Knockout Techniques ; Glucosamine ; biosynthesis ; genetics ; Repressor Proteins ; genetics

The influence of different affinity tags on enzyme characteristics varies. The (S)-carbonyl reductase 2 (SCR2) from Candida parapsilosis can reduce 2-hydroxyacetophenone, which is a valuable prochiral ketones. Different affinity tags, i.e. his-tag, strep-tag and MBP-tag, were attached to the N terminus of SCR2. These tagged SCR2 enzymes, i.e. his6-SCR2, strep-SCR2 and MBP-SCR2, were heterologously expressed in Escherichia coli and purified to study their characteristics towards 2-hydroxyacetophenone reduction. Affinity tags did affect the characteristics of the recombinant SCR2 enzymes. Specifically, affinity tags affect the stability of recombinant SCR2 enzymes: 1) At pH 6.0, the remaining enzyme activities of his6-SCR2 and strep-SCR2 were only 95.2% and 90.0% of the untagged SCR2, while that of MBP-SCR2 was 1.2 times of the untagged SCR2 after incubating for 13 h at 30 °C. 2) The half-life of MBP-SCR2 at 50 °C was 26.6%-48.8% longer than those of strep-SCR2, his6-SCR2 and untagged SCR2. 3) The kcat of MBP-SCR2 was about 1.25-1.45 times of that of small affinity-tagged and untagged SCR2 after storing at -80 °C for 60 d. Structural informatics indicated that the α-helices at the C terminus of MBP-SCR2 contributed to the stability of the N terminus of fusion protein of SCR2. Data from circular dichroism showed that the MBP-tag has some influence on the secondary structure of SCR2, while melting temperature analysis demonstrated that the Tm of the recombinant MBP-SCR2 was about 5 °C higher than that of the untagged SCR2. This study obtained an efficient and stable recombinant SCR2, i.e. the MBP-SCR2. Moreover, this study could serve as a reference for other researchers to evaluate and select appropriate affinity tags for their research.
Alcohol Oxidoreductases ; Escherichia coli/genetics* ; Recombinant Fusion Proteins/genetics*

Adhesins, Escherichia coli ; genetics ; Bacterial Typing Techniques ; Escherichia coli Proteins ; genetics ; Fimbriae Proteins ; genetics ; Genes, Bacterial ; Genotype ; Uropathogenic Escherichia coli ; classification ; genetics

OBJECTIVETo construct enterohemorrhagic Escherichia coli (EHEC) O157:H7 strains with delection espF gene and its nucleotide fragment and with espF gene complementation.

METHODSA pair of homologous arm primers was designed to amplify the gene fragment of kanamycin resistance, which was transformed into EHEC O157:H7 EDL933w strain via the PKD46 plasmid by electroporation. The replacement of the espF gene by kanamycin resistance gene through the PKD46-mediated red recombination system was confirmed by PCR and sequencing. The entire coding region of espF along with its nucleotide fragment was amplified by PCR and cloned into pBAD33 plasmid, which was transformed into a mutant strain to construct the strain with espF complementation. RT-PCR was used to verify the transcription of espF and its nucleotide fragment in the complemented mutant strain.

RESULTS AND CONCLUSIONWe established EHEC O157:H7 EDL933w strains with espF gene deletion and with espF gene complementation. Both espF and its nucleotide fragment were transcribed in the complemented mutant strain. The two strains provide a basis for further study of the regulatory mechanism of espF.

Carrier Proteins ; genetics ; DNA Primers ; Escherichia coli O157 ; genetics ; Escherichia coli Proteins ; genetics ; Gene Deletion ; Plasmids ; Polymerase Chain Reaction

High-level expression of phytase with high specific activity is an effective way to improve phytase fermentation potency and reduce its production cost. The gene appA encoding Escherchia coli phytase AppA with high specific activity was modified and artificially synthesized according to the bias in codon choice of the high expression gene in Pichia pastoris without changing the amino acid sequence of the AppA. The modified gene, appA-m, was inserted in the Pichia pastoris expression vector pPIC9, then introduced into the host Pichia pastoris by electroporation. The Pichia pastoris recombinants for phytase overexpression were screened by enzyme activity analysis and SDS-PAGE. The result of Southern blotting analysis of the recombinant yeast indicated that only one copy of the appA-m gene was integrated into the genome of Pichia pastoris. The result of Northern analysis of the recombinant yeast showed that the modified gene was effectively transcribed. SDS-PAGE analysis of the phytase expressed in Pichia pastoris revealed that the phytase was overexpressed and secreted into the medium supernatant. There are three phytase proteins with apparent molecular weight in approximately 50kD, 52kD and 54kD respectively in the media, which are larger in the size than the native phytase from E. coli. The results of N-terminal sequecing and deglycosylation of the expressed phytase in Pichia pastoris proved that the expressed phytase were glycosylated protein with different glycosylation degree. The expressed phytase Pichia pastoris shared similar pH and temperature optima to those of the natural phytase from E. coli and had highly resistant to pepsin digestion. In 5-L fermentor, after induced by 0.5% methanol for 120 h, the expression level of phytase protein was 2.5 mg/mL, and the phytase activity (fermentation potency) exceeded 7.5 x 10(6) IU/mL, which was the highest among those of all kinds of recombinant strains reported now.
6-Phytase ; genetics ; metabolism ; Escherichia coli ; enzymology ; Escherichia coli Proteins ; genetics ; Fermentation ; Pichia ; genetics ; Plasmids ; Recombinant Proteins ; biosynthesis

OBJECTIVETo construct enterohemorrhagic Escherichia coli (EHEC) O157: H7 ppk gene deletion strains and study its biological characteristics.

METHODSThe gene fragment of kanamycin resistance was amplified using a pair of homologous arm primers whose 5' and 3' ends were homologous with ppk gene and kanamycin resistance gene, respectively. EHEC O157: H7 EDL933w competent strains were prepared and transformed via electroporation with the amplification products. The ppk gene was replaced by kanamycin resistance gene using pKD46-mediated Red recombination system. The recombinant strain was confirmed by PCR and sequencing, and its morphology, growth ability and adhesion were assessed using Gram staining, OD600 value and Giemsa staining.

RESULTS AND CONCLUSIONWe established a ppk-deleted EHEC O157:H7 EDL933w strain with kanamycin resistance and compared the biological characteristics of the wild-type and mutant strains, which may facilitate further study of the regulatory mechanism of ppk gene.

DNA Primers ; Escherichia coli O157 ; genetics ; Escherichia coli Proteins ; genetics ; Gene Deletion ; Phosphotransferases (Alcohol Group Acceptor) ; genetics ; Polymerase Chain Reaction

Objective: To investigate the antimicrobial resistance of food-borne diarrheagenic Escherichia coli (DEC) and the prevalence of mcr genes that mediates mobile colistin resistance in parts of China, 2020. Methods: For 91 DEC isolates recovered from food sources collected from Fujian province, Hebei province, Inner Mongolia Autonomous Region and Shanghai city in 2020, Vitek2 Compact biochemical identification and antimicrobial susceptibility testing platform was used for the detection of antimicrobial susceptibility testing (AST) against to 18 kinds of antimicrobial compounds belonging to 9 categories, and multi-polymerase chain reaction (mPCR) was used to detect the mcr-1-mcr-9 genes, then a further AST, whole genome sequencing (WGS) and bioinformatics analysis were platformed for these DEC isolates which were PCR positive for mcr genes. Results: Seventy in 91 isolates showed different antimicrobial resistance levels to the drugs tested with a resistance rate of 76.92%. The isolates showed the highest antimicrobial resistance rates to ampicillin (69.23%, 63/91) and trimethoprim-sulfamethoxazole (59.34%, 54/91), respectively. The multiple drug-resistant rate was 47.25% (43/91). Two mcr-1 gene and ESBL (extended-spectrum beta-lactamase) positive EAEC (enteroaggregative Escherichia coli) strains were detected. One of them was identified as serotype of O11:H6, which showed a resistance profile to 25 tested drugs referring to 10 classes, and 38 drug resistance genes were predicted by genome analysis. The other one was O16:H48 serotype, which was resistant to 21 tested drugs belonging to 7 classes and carried a new variant of mcr-1 gene (mcr-1.35). Conclusion: An overall high-level antimicrobial resistance was found among foodborne DEC isolates recovered from parts of China in 2020, and so was the MDR (multi-drug resistance) condition. MDR strains carrying multiple resistance genes such as mcr-1 gene were detected, and a new variant of mcr-1 gene was also found. It is necessary to continue with a dynamic monitoring on DEC contamination and an ongoing research into antimicrobial resistance mechanisms.
Humans ; Colistin/pharmacology* ; Anti-Bacterial Agents/pharmacology* ; Escherichia coli Infections/epidemiology* ; Escherichia coli Proteins/genetics* ; Drug Resistance, Bacterial/genetics* ; China/epidemiology* ; Escherichia coli ; Plasmids/genetics* ; Microbial Sensitivity Tests