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

BACKGROUNDIn prokaryotic organisms, the mechanism responsible for the accurate partition of newly replicated chromosomes into daughter cells is incompletely understood. Segregation of the replication terminus of the circular prokaryotic chromosome poses special problems that have not previously been addressed. The aim of this study was to investigate the roles of several protein components (MreB, MreC, and MreD) of the prokaryotic cytoskeleton for the faithful transmission of the chromosomal terminus into daughter cells.

METHODSStrain LQ1 (mreB::cat), LQ2 (mreC::cat), and LQ3 (mreD::cat) were constructed using the Red recombination system. LQ11/pLAU53, LQ12/pLAU53, LQ13/pLAU53, LQ14/pLAU53, and LQ15/pLAU53 strains were generated by P1transduction of (tetO) 240 -Gm and (lacO) 240 -Km cassettes from strains IL2 and IL29. Fluorescence microscopy was performed to observe localization pattern of fluorescently-labeled origin and terminus foci in wild-type and mutant cells. SOS induction was monitored as gfp fluorescence from PsulA-gfp in log phase cells grown in Luria-Bertani medium at 37°C by measurement of emission at 525 nm with excitation at 470 nm in a microplate fluorescence reader.

RESULTSMutational deletion of the mreB, mreC, or mreD genes was associated with selective loss of the terminus region in approximately 40% of the cells within growing cultures. This was accompanied by significant induction of the SOS DNA damage response, suggesting that deletion of terminus sequences may have occurred by chromosomal cleavage, presumably caused by ingrowth of the division septum prior to segregation of the replicated terminal.

CONCLUSIONSThese results imply a role for the MreBCD cytoskeleton in the resolution of the final products of terminus replication and/or in the specific movement of newly replicated termini away from midcell prior to completion of septal ingrowth. This would identify a previously unrecognized stage in the overall process of chromosome segregation.

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*

Arginine deiminase (ADI) has been studied as a potential anti-cancer agent for inhibiting arginine-auxotrophic tumors (such as melanomas and hepatocellular carcinomas) in phase III clinical trials. In this work, we studied the molecular mechanism of arginine deiminase activity by site-directed mutagenesis. Three mutation sites, A128, H404 and 1410, were introduced into wild-type ADI gene by QuikChange site-directed mutagenesis method, and four ADI mutants M1 (A128T), M2 (H404R), M3 (I410L), and M4 (A128T, H404R) were obtained. The ADI mutants were individually expressed in Escherichia coli BL21 (DE3), and the enzymatic properties of the purified mutant proteins were determined. The results show that both A128T and H404R had enhanced optimum pH, higher activity and stability of ADI under physiological condition (pH 7.4), as well as reduced K(m) value. This study provides an insight into the molecular mechanism of the ADI activity, and also the experimental evidence for the rational protein evolution in the future.
Escherichia coli ; metabolism ; Hydrolases ; genetics ; metabolism ; Mutagenesis, Site-Directed

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

Lysis is a common functional module in synthetic biology and is widely used in genetic circuit design. Lysis could be achieved by inducing expression of lysis cassettes originated from phages. However, detailed characterization of lysis cassettes hasn't been reported yet. Here, we first adopted arabinose- and rhamnose-inducible systems to develop inducible expression of five lysis cassettes (S₁₀₅, A52G, C51S S76C, LKD, LUZ) in Escherichia coli Top10. By measuring OD₆₀₀, we characterized the lysis behavior of strains harboring different lysis cassettes. These strains were harvested at different growth stages, induced with different concentrations of chemical inducers, or contained plasmids with different copy numbers. We found that although all five lysis cassettes could induce bacterial lysis in Top10, lysis behaviors differed a lot at various conditions. We further found that due to the difference in background expression levels between strain Top10 and Pseudomonas aeruginosa PAO1, it was hard to construct inducible lysis systems in strain PAO1. The lysis cassette controlled by rhamnose-inducible system was finally inserted into the chromosome of strain PAO1 to construct lysis strains after careful screen. The results indicated that LUZ and LKD were more effective in strain PAO1 than S₁₀₅, A52G and C51S S76C. At last, we constructed an engineered bacteria Q16 using an optogenetic module BphS and the lysis cassette LUZ. The engineered strain was capable of adhering to target surface and achieving light-induced lysis by tuning the strength of ribosome binding sites (RBSs), showing great potential in surface modification.
Rhamnose/pharmacology* ; Plasmids/genetics* ; Pseudomonas aeruginosa ; Escherichia coli/metabolism*

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

We studied the ability of lpdA gene knockout Escherichia coli to ferment different sugars in mineral salts medium for the production of pyruvate. The sugars studied were glucose, fructose, xylose and mannose at a concentration of 10 g/L. At the same time, effect of inoculum size on lpdA fermentation with glucose was studied. The strain was able to use all sugars for biomass generation and pyruvate production. The lpdA knockout mutant converted glucose, fructose, xylose and mannose to pyruvate with yields of 0.884 g/g, 0.802 g/g, 0.817 g/g and 0.808 g/L, respectively. The pyruvate accumulation curve coupled with cell growth except for mannose as carbon source. When the inoculation size increased, the rate of glucose consumption, pyruvate accumulation and cell growth increased but lower pyruvate concentration. This study demonstrates that E. coli lpdA mutant has the potential to produce pyruvic acid from xylose and mannose.
Carbon ; metabolism ; Dihydrolipoamide Dehydrogenase ; genetics ; Escherichia coli ; genetics ; metabolism ; Escherichia coli Proteins ; genetics ; Fermentation ; Fructose ; metabolism ; Gene Knockout Techniques ; Glucose ; metabolism ; Mannose ; metabolism ; Pyruvic Acid ; metabolism ; Xylose ; metabolism

Gene expression is regulated by different transcriptional regulators. The transcriptional regulator isocitrate lyase regulator (IclR) of Escherichia coli represses the expression of the aceBAK operon that codes for the glyoxylate pathway enzymes. In this study, physiological and metabolic responses of the deletion of the ic1R gene in E. coli BW25113 were investigated based on the quantification and analysis of intracellular metabolic fluxes. The knockout of the iclR gene resulted in a decrease in the growth rate, glucose uptake rate and the acetate secretion rate, but a slight increase in biomass yield. The latter could be attributed to the lowered metabolic fluxes through several CO2 generating pathways, including the redirection of 33% of isocitrate directly to succinate and malate without CO2 production as well as the reduced flux through the pentose phosphate pathway. Furthermore, although the glyoxylate shunt was activated in the iclR mutant, the flux through phosphoenolpyruvate (PEP) carboxykinase kept almost unchanged, implying an inactive PEP-glyoxylate cycle and no extra loss of carbon atoms in the mutant strain. Both the reduced glucose uptake rate and the active glyoxylate shunt were responsible for the minor decrease in acetate secretion in the ic1R knockout strain compared to that in the wild-type E. coli strain.
Carbon Isotopes ; metabolism ; Escherichia coli ; enzymology ; genetics ; Escherichia coli Proteins ; genetics ; metabolism ; Gene Knockout Techniques ; Isocitrate Lyase ; genetics ; metabolism ; Metabolic Networks and Pathways ; genetics ; Repressor Proteins ; genetics ; metabolism

Animals ; Bacterial Proteins ; genetics ; metabolism ; Chickens ; microbiology ; Escherichia coli ; genetics ; metabolism ; Genotype ; beta-Lactamases ; genetics ; metabolism