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*

Background:blaTEM, bla SHV, blaCTX \ufffd?M, blaOXA genes encode for extended spectrum \u03b2 \ufffd?lactamases resistance to broad \ufffd?spectrumcephalosporins. Many species belonging the family Enterobacteriaceae possess these genes. Objectives: To determine the distribution of blaTEM, bla SHV, blaCTX \ufffd?M and blaOXA genes in enteroaggregation E.coli (EAEC) strains. Subjects and method: 67 EAEC strains causing diarrhea and 18 strains isolated from healthy children were screened by PCR with primers specific to blaTEM, bla SHV, blaCTX \ufffd?M \ufffd?1and blaOXA genes. Results: The prevalence of ESBL genes in diarrheagenic EAEC strains and those isolated from healthy children were 83.6 and 72.2 %, respectively. The highest prevalence blaTEM gene (82% in diarrheagenic EAEC strains and 72.2% in isolated from healthy children) was followed by that of blaOXA gene (11.9 and 11.1% in two EAEC groups). Only 2 strains possess blaSHV gene. The blaCTX \ufffd?M \ufffd?1 was not detected in any EAEC strain. Conclusion: our findings have not only provided additional understanding of the distribution of blaTEM, bla SHV, blaCTX \ufffd?M - 1 and blaOXA genes in EAEC strains but also have a given significance in selecting antibiotics for treatment.
beta-Lactamases/ genetics ; Escherichia coli ;

Objective: To evaluate the typing and clinical application effect based on clustered regularly interspaced short palindromic repeats (CRISPRs), serotype, and Multilocus Sequence Typing (MLST). Methods: The spacers, serotype and sequence type (ST) were obtained with CRISPRsFinder, SeroTypeFinder and MLST. PCR was used to amplify the CRISPRs, and the spacers were used to predict serotype and ST, then comparing with the serotype and ST. Results: We defined the I-E CRISPR/Cas as CT-Ⅰ, I-F CRISPR/Cas as CT-Ⅱ, and only CRISPR3-4 as CT-Ⅲ. We designated each unique arrangement spacer profile as a unique CRISPRs type. A total of 79 CT types, 76 serotypes, and 66 STs were identified. The CRISPRs typing was the most discriminating, with the Simpson index of 0.936, having the highest correlation with serology with the adjusted Rand index of 0.908. The CRISPRs type could divide the same serotype (ST) into two subtypes [O157∶H7(ST11), O104∶H4(ST678), and O26∶H11(ST21)]. The detection rates of CRISPR1, CRISPR2, CRISPR3, CRISPR4, and CRISPR3-4 were 81.1%, 94.5%, 1.4%, 1.4%, and 4.6%, with the accuracy rate of 95.0% and 100.0% according to the spacers to forecast O157∶H7 (ST11) and ST131. Conclusion: Based on the CRISPRs spacer, this method can be used as an essential molecular typing for E.coli, as it presents a good typing and clinical application effect.
Escherichia coli/genetics* ; Escherichia coli Infections ; Humans ; Multilocus Sequence Typing

Pullulanase is a starch debranching enzyme, which is difficult in secretory expression due to its large molecular weight. Vibrio natriegens is a novel expression host with excellent efficiency in protein synthesis. In this study, we achieved secretory expression of the full-length pullulanase PulA and its truncated mutant PulN2 using V. natriegens VnDX strain. Subsequently, we investigated the effects of signal peptide, fermentation temperature, inducer concentration, glycine concentration and fermentation time on the secretory expression. Moreover, the extracellular enzyme activities of the two pullulanases produced in V. natriegens VnDX and E. coli BL21(DE3) were compared. The highest extracellular enzyme activity of PulA and PulN2 in V. natriegens VnDX were 61.6 U/mL and 64.3 U/mL, which were 110% and 62% that of those in E. coli BL21(DE3), respectively. The results indicated that V. natriegens VnDX can be used for secretory expression of the full-length PulA with large molecular weight, which may provide a reference for the secretory expression of other large molecular weight proteins in V. natriegens VnDX.
Escherichia coli/genetics* ; Fermentation ; Vibrio/genetics*

Polyhydroxyalkanoate depolymerase (PHAD) can be used for the degradation and recovery of polyhydroxyalkanoate (PHA). In order to develop a PHAD with good stability under high temperature, PHAD from Thermomonospora umbrina (TumPHAD) was heterelogously expressed in Escherichia coli BL21(DE3). At the same time, a mutant A190C/V240C with enhanced stability was obtained via rational design of disulfide bonds. Characterization of enzymatic properties showed that the mutant A190C/V240C had an optimum temperature of 60 ℃, which was 20 ℃ higher than that of the wild type. The half-life at 50 ℃ was 7 hours, at 50 ℃ which was 21 times longer than that of the wild type. The mutant A190C/V240C was used for the degradation of polyhydroxybutyrate (PHB), one of the typical PHA. At 50 ℃, the degradation rate of PHB being treated for 2 hours and 12 hours was 2.1 times and 3.8 times higher than that of the wild type, respectively. The TumPHAD mutant A190C/V240C obtained in this study shows tolerance to high temperature resistance, good thermal stability and strong PHB degradation ability, which may facilitate the degradation and recovery of PHB.
Thermomonospora ; Actinomycetales ; Escherichia coli/genetics* ; Polyhydroxyalkanoates

Tyrosol is a natural polyphenolic product that is widely used in chemical, pharmaceutical and food industries. Currently, the de novo synthesis of tyrosol by Escherichia coli suffers from issues such as low cell density and poor yield. Therefore, the phenylpyruvate decarboxylase mutant ARO10^F138L/D218G obtained in our previous study was fused with an alcohol dehydrogenase from different microorganisms for fusion expression, and the optimal ARO^{10F138L/D218G}-L-YahK produced 1.09 g/L tyrosol in shake flasks. In order to further improve tyrosol production, feaB, a key gene in the competing pathway of 4-hydroxyphenylacetic acid, was knocked out, and the resulted strain produced 1.26 g/L tyrosol with an increase of 21.15% compared to that of the control. To overcome the low cell density in tyrosol fermentation, the quorum-sensing circuit was used to dynamically regulate the tyrosol synthesis pathway, so as to alleviate the toxic effect of tyrosol on chassis cells and relieve the growth inhibition. Using this strategy, the yield of tyrosol was increased to 1.74 g/L, a 33.82% increase. In a 2 L fermenter, the production of tyrosol in the engineered strain TRFQ5 dynamically regulated by quorum-sensing reached 4.22 g/L with an OD₆₀₀ of 42.88. Compared with those in the engineered strain TRF5 statically regulated by induced expression, the yield was increased by 38.58% and the OD₆₀₀ was enhanced by 43.62%. The combination of blocking the competing pathway using gene knockout technology, and reducing the inhibitory effect of tyrosol toxicity on chassis cells through quorum-sensing dynamic regulation increased the production of tyrosol. This study may facilitate the biosynthesis of other chemicals with high toxicity.
Escherichia coli/genetics* ; Biological Products ; Bioreactors ; Fermentation

Curcumin is exclusively isolated from Zingiberaceae plants with a broad spectrum of bioactivities. In the present study, we used the diketide-CoA synthase (DCS) and curcumin synthase (CURS) genes to construct a non-natural fusion gene encoding diketide-CoA synthase::curcumin synthase (DCS::CURS). This fusion protein, together with the acetyl coenzyme A carboxylase (ACC) and the 4-coumarate coenzyme A ligase (4CL), were introduced into Escherichia coli for the production of curcumin from ferulic acid. The process is divided into two stages, the growth stage using LB medium and the fermentation stage using the modified M9 medium. The yield of curcumin reached 386.8 mg/L by optimizing the induction of protein expression in the growth stage, and optimizing the inoculum volume, medium composition and fermentation time in the fermentation stage, as well as the addition of macroporous resin AB-8 into the second medium to attenuate the toxicity of the end product. The exploitation of the non-natural fusion protein DCS::CURS for the production of curcumin provides a new alternative to further promoting the production of curcumin and the related analogues.
Curcumin/pharmacology* ; Escherichia coli/genetics* ; Fermentation

L-Homoserine is a non-essential amino acid that is often used as an important platform compound and additive in industrial production. To improve the production efficiency, a previously constructed L-homoserine producing strain E. coli H0-0 was used as a chassis for further metabolic modification. Firstly, the ppc and pyccgP458S genes were overexpressed to optimize the Kreb's cycle. Subsequently, thrAC1034T and lysCcgC932T were overexpressed to improve the product synthesis, followed by inactivation of iclR gene to reduce the accumulation of by-products. The introduction of three sucrose metabolism genes, scrA, scrB and scrK, enabled E. coli to ferment sucrose. The titer of L-homoserine increased from 3.2 g/L to 11.1 g/L.
Escherichia coli/genetics* ; Homoserine ; Metabolic Engineering ; Serine

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*