Knockout of the ptsG gene in Escherichia coli and cultural characterization of the mutants / 生物工程学报

Metabolic engineering provide powerful tools for the systematic manipulation of cellular metabolic activities. The ptsG gene for glucose-specific transporter Enzyme II CBGlc of the phosphotransferase system was knock-out so as to reduce the accumulation of acetic acid in the high cell-density culture of Escherichia coli on excess glucose. The chloramphenicol-resistant cassette with short shared sequences on both ends generated by PCR was electroporated into Escherichia coli DH5alpha and JM109. Recombination between linear DNA cassettes and Escherichia coli chromosomes took place by Red recombinase functions. Therefore, the ptsG gene was disrupted to construct the mutants called DH5alphaP and JM109P. There was no difference between the mutants and parent strains in LB media.However, in LB media supplemented with glucose, the mutants of Escherichia coli deficient in ptsG showed greater biomass, together with exploiting more glucose. The maximal cell density obtained with DH5alphaP was approximately 3 times more than that of DH5alpha, then the result of JM109P increased fourfold. The products of recombinant protein TNF respectively accounted for 24.3% of total cellular protein in DH5alphaP with A600 8.28 and 20.8% of total cellular protein in JM109P with A600 7.62. The specific volume expression amount of TNF was greater in the ptsG mutant than in its parent strain. These results demonstrate that the ptsG-mutant strains will be available for high cell-density culture.

Cloning and expression of L-N-carbamoylase gene from Arthrobacter BT801 in Escherichia coli / 生物工程学报

Hydantoin-utility-enzyme is widely used in enzymic production of various amino acids. One of its component, carbamoylase, is responsible for the conversion of N-carbamylamino acids to corresponding amino acids, which is crucial for the stereoselectivity and rate limiting. To improve the production of the enzyme, an L-N-carbamoylase gene from Arthrobacter BT801, a hydantoinase producting strain being able to convert 5-benzylhydantoin to phenylalanine, was cloned into E. coli. The gene was highly expressed in E. coli M15 under control of T5 promoter. A protein band about 44kD was detected by SDS-PAGE in the recombinant cell lysate. The objective product, which is principally in soluble form, represented 40% of total cell protein. The N-carbamoylase specific activity of the recombinant M15/pQE60- hyuC is 53 times higher than that of Arthrobacter BT801. The total biotransformation activity increased 8.1 times when. M15/pQE60-hyuC was added into the Arthrobacter BT801 reaction system. The successful expression of the enzyme is significant for the application of the hydantoinase producing strain or the enzyme thereof.

Construction of gene library of Arthrobacter BT801 and isolation & expression of hydantoinase gene / 生物工程学报

Hydantoinase can be widely used in enzymic production of various amino acids. In order to obtain the hydantoinase genes in Arthrobacter BT801, its chromatosomal DNA is isolated and partialy digested with Sau3A I to collect fragments of about 30kb. Then, this fragment is inserted into the Hpa I and Pst I site of cosmid pKC505. The genomic library was thus constructed by packing in vitro with lambda phage package protein and transfecting E. coli DH5alpha. A positive transformant was selected from the library using thin layer chromatography and other methods. A DNA fragment containing complete hydantoinase genes was sequenced by sub-cloning into pUC18. The gene can express active protein under control of its own promoter and T5 promoter in E. coli. The isolation of the gene established foundition for research and application of the hydantoinase.

Advances in the Research on the Brucella Intracellular Life / 微生物学通报

Brucella organisms are facultative intracellular bacteria capable of surviving inside professional and non-professional phagocytes.Upon cell contact the bacteria is internalized via receptor molecules.Once inside cells,Brucella localizes in early phagosomes,where it avoids fusion with late endosomes and lysosomes.Then,the bacterium redirects its trafficking to autophagosomes and finally reaches the endoplasmic reticulum,the replicating niche.Once inside the endoplasmic reticulum,Brucella extensively replicates without restricting basic cellular functions or inducing damage to cells.Invasion,intracellular trafficking and replication of Brucella organisms in professional and non-professional phagocytes and the molecular determinants involving Brucella intracellular life are reviewed in this article.

Construction of Brucella Unmarked Deletion Mutant by Using Conventional Cloning Vector as Suicide Plasmid / 微生物学通报

Construction of mutant strain is an essential method in pathogenesis researches. The conventional method for Brucella unmarked deletion mutant construction is based on suicide plasmid, but the efficiency is very low. In the present study, we first optimized the electroporation parameters, and then, the cloning plasmid pEX18Gm containing sacB was successfully used to construct unmarked deletion mutant of the type IV secretion system. This indicated that by using conventional cloning plasmid as suicide plasmid in Brucella, unmarked deletion mutants can be constructed with high efficiency.

A SIMPLE METHOD OF TRANSCONJUGATIVE CLONING WITH HIGH EFFICIENCY / 微生物学通报

In order to establish a method by which the recombinant suicide plasmids integrated on the chromosome could be recircled, A simple method of transconjugative cloning was established with the helper plasmids pMT999 or pRK2013 and fusion strains of Shigella flexneri which were obtained by screening with in vivo expression technology. And the cloning efficiency with this method is very high.

EXPRESSION OF L-N-CARBAMOYLASE GENE IN PICHIA PASTORIS / 微生物学通报

N-carbamoylase is a part of hydantoinase operon which can transform N-carbamoylamino acid to corresponding ammo acids. The L-N-carbamoylase of Arthrobacter BT801, codied by the HyuC gene, is the rate-limiting and the only stereoselective enzyme. HyuC DNA fragment was amplified by PCR from the plasmid of pUC18-169. The target fragment was introduced into pPIC3. 5K plasmid to construct the pPIC3. 5K-hyuC expressing vector which was then transduced into Pichia pastoris GS115 cells after being linearized by BglⅡ digestion. Multi-copies insertion transformants were screened on G418 plates. The recombinant protein was proved to have biological activity of hydrolyzing N-carbamoylphenylalanine into phenylalanine through enzyme activity determination.