含铁肠杆菌素受体调节蛋白VPA0148对副溶血弧菌毒力的影响

副溶血弧菌(Vibrio parahaemolyticus)是一种嗜盐性革兰氏阴性菌,广泛分布于海洋环境中,能够引起肠胃炎、伤口感染以及败血症,是人类重要的病原菌之一。宿主体内被认为是一种低铁环境,能够激发致细菌的毒力。副溶血弧菌能够分泌弧菌素或利用外源铁载体来获取铁。在低铁条件下,编码双组份调控系统的基因簇VPA0148-VPA0149转录上调,使含铁肠杆菌素受体PeuA转录出有活性的蛋白。VPA0148编码产物为一个响应调节因子,具有一个磷酸基团接收结构域和一个DNA结合结构域。本研究发现,VPA0148的缺失增强了菌株的生物膜形成能力和对斑马鱼的致死能力,同时能够促进菌株在低铁环境中的生长,并增强菌株的群集运动。研究结果表明含铁肠杆菌素受体调节蛋白VPA0148对副溶血弧菌致病力具有调控作用,增进了对铁调节副溶血弧菌毒力机制的认识。

阴沟肠杆菌感染致新生儿颅腔积气一例报告

目的含气的脑炎在新生儿非常罕见。我们报道1例日龄为5d的新生儿，因败血症并发颅内感染而导致颅腔大量积气。对新生儿阴沟肠杆菌感染引起颅腔积气患儿进行临床和疾病转归及泸州地区阴沟肠杆菌耐药分析。方法对本例阴沟肠杆菌感染引起脑膜炎、颅腔大量积气的患儿进行蓝光治疗、抗生素、静脉补液、纠正酸中毒及支持治疗，反复检查血常规、CRP、头颅CT、血培养、脑积液常规、脑脊液培养等。结果血培养及脑脊液培养均为阴沟肠杆菌，头颅CT表现为颅腔大量积气，随着病情好转颅腔气体逐渐吸收后形成严重颅腔积水，并遗留严重神经系统后遗症。结论本病案强调阴沟肠杆菌感染在新生儿是应引起足够的重视，新生儿阴沟肠杆菌颅腔感染早期临床表现不典型，可以导致颅腔积气，对喹诺酮类敏感率93．75％-100％、庆大霉素敏感率73．33％、亚胺培南敏感率94．12％，对半合成青霉素、头孢菌素三代易产生耐药性，病死率高，存活后遗留有严重神经系统后遗症。

Establishment and Application of a Real-time PCR Method for Detecting stx2 Gene in Shiga Toxin-producing Escherichia coli(STEC)

[Objective] This study aimed to establish a real-time PCR method for de- tecting stx2 gene in Shiga toxin-producing E. coli （STEC）. [Method] According to the known STEC stx2 gene sequences published in GenBank, PCR primers and probes were designed based on the conserved region to construct recombinant plasmid as a positive template, thus optimizing the reaction conditions and establishing the real- time PCR method. [Result] A standard curve was established based on the opti- mized real-time PCR system, indicting a good linear correlation between the initial template concentration and Ct value, with the correlation coefficient F^e of above 0.995. The established method had a good specificity, without non-specific amplifica- tion for 10 non-STEC intestinal bacterial strains; the detection limit of initial template was 1.0x102 copies/μI, indicating a high sensitivity; furthermore, the coefficients of variation within and among batches were lower than 1% and 5% respectively, sug- gesting a good repeatability. [Conclusion] In this study, a real-time PCR method was successfully established for detecting STEC stx2 gene, which provided technical means for rapid detection of STEC in samples.

AtTHIC, a gene involved in thiamine biosynthesis in Arabidopsis thaliana

Thiamine （vitamin B1） is an essential compound for organisms. It contains a pyrimidine ring structure and a thiazole ring structure. These two moieties of thiamine are synthesized independently and then coupled together. Here we report the molecular characterization of AtTHIC, which is involved in thiamine biosynthesis in Arabidopsis. AtTHIC is similar to Escherichia coli ThiC, which is involved in pyrimidine biosynthesis in prokaryotes. Heterologous expression of AtTHIC could functionally complement the thiC knock-out mutant of E. coll. Downregulation of AtTHIC expression by T-DNA insertion at its promoter region resulted in a drastic reduction of thiamine content in plants and the knock-down mutant thicl showed albino （white leaves） and lethal phenotypes under the normal culture conditions. The thicl mutant could be rescued by supplementation of thiamine and its defect functions could be complemented by expression ofAtTHIC cDNA. Transient expression analysis revealed that the AtTHIC protein targets plastids and chloroplasts. AtTHIC was strongly expressed in leaves, flowers and siliques and the transcription of AtTHIC was downregulated by extrinsic thiamine. In conclusion, AtTHIC is a gene involved in pyrimidine synthesis in the thiamine biosynthesis pathway of Arabidopsis, and our results provide some new clues for elucidating the pathway of thiamine biosynthesis in plants.

Chloromycetin resistance of clinically isolated E coli is conversed by using EGS technique to repress the Chloromycetin acetyl transferase

AIM： To explore the possibility of repression of chloromycetin （Cm） acyl transferase by using external guided sequence （EGS） in order to converse the clinical E coli isolates from Cm- resistant to Cm- sensitive. METHODS： EGS directed against chloromycetin acetyl transferase gene （cat） was cloned to vector pEGFP-C1 which contains the kanamycin （Kin） resistance gene. The recombinant plasmid pEGFP-C1＋EGScatl＋cat2 was constructed and the blank vector without EGS fragment was used as control plasmids. By using the CaCl2 transformation method, the recombinant plasmids were introduced into the clinically isolated Cm resistant but Km sensitive E coli strains. Transformants were screened on LB agar plates containing Kin. Extraction of plasmids and PCR were applied to identify the positive clones. The growth curve of EGS transformed bacteria cultured in broth with Cm resistance was determined by using spectrophotometer at A600. Drug sensitivity was tested in solid culture containing Cm by using KB method. RESULTS： Transformation studies were carried out on 16 clinically isolated Cm-resistant （250 μg/mL of Cm） E colistrains by using pEGFP-C1-EGScatlcat2 recombinant plasmid. Transformants were screened on LB-agar plates containing Km after the transformation using EGS. Of the 16 tested strains, 4 strains were transformed successfully. Transformants with EGS plasmid showed growth inhibition when grown in liquid broth culture containing 200 μg/mL of Cm. In drug sensitivity test, these strains were sensitive to Cm on LB-agar plates containing 200 μg/mL of Cm. Extraction of plasmids and PCR amplification showed the existence of EGS plasmids in these four transformed strains. These results indicated that the Cat of the four clinical isolates had been suppressed and the four strains were converted to Cm sensitive ones. CONCLUSION： The EGS directed against Cat is able to inhibit the expression of Cat, and hence convert Cm- resistant bacteria to Cm-sensitive ones. Thus, the EGS has the capability of converting the phenotype of clinical drug-resistant isolates strains to drug-sensitive ones.

Sedimentary response to volcanic activity in the Okinawa Trough since the last deglaciation

To investigate the relationship between volcanic activity and sediment record on regional and temporal scales,158 surface sediment samples were collected from the East China Sea Shelf to the northern Okinawa Trough (OT),and two cores recovered in the northern and southern OT,respectively.Mineralogy,grain-size,and geochemical analyses of those samples show that:1) volcanic glass,volcanic-type pyroxene,hypersthenes,and magnetite increase in sediment influenced by volcanic activity;2) sediment grain sizes (and also silt content) increase in ash layers;and 3) the contents of Na2O and Zr are higher,while terrigenous elements,e.g.,TFe2O3 and K2O,and biogenous compositions,e.g.,CaO and Sr,are relatively lower in ash layers than those of non-ash layers.The distribution of volcanic ash has three distinguishing characteristics:1) volcanic ash is more abundant in the northern and central OT than the southern OT;2) volcanic ash increases from continental shelf to the trough;3) the sediment during the last 12 000 a suggests stronger volcanic events than during 15 000-12 000 a.The eruptive locations,frequency,and volume of calderas are among the most important factors controlling the distributions of volcanic ash.In addition,the main Kuroshio warm current that extends northward probably impeded the diffusion of volcanic ash to the west and south in the OT.However,a southward current probably carried some volcanic ash toward southern OT.

Clinical features of familial adenomas polyps in Chinese and establishment of its immortal lymphocyte cell lines

AIM： To reserve the rare Chinese familial adenomas polyp （FAP） family resource and to investigate the clinical features of FAP in Chinese for its diagnosis. METHODS： Clinical features of patients with FAP were investigated. If there is any question, their medical records were verified. Blood sample was taken and lymphocyte immortal cell lines were established with modified EB-transformation methods. Congenital hypertrophy of retinal pigment epithelium （CHRPE） was checked by an experienced ophthalmologist. RESULTS： Twenty seven families including 21 classical FAP （CFAP） families, 3 attenuated FAP （AFAP） families, and 3 suspected AFAP families were investigated. A total of 116 lymphocyte immortal cell lines were established from 26 families. In all the FAP families, colorectal cancer occurred at the mean age of 42.84 years. Of the 16 families checked, 15 （93.75%） had CHRPE. The mean number of patients suffering from colorectal neoplasm was 3.14 in CFAP families and 2.0 in AFAP families （P 〈 0.01）. The mean oldest age at diagnosis of FAP was 41.75 years in CFAP families, and 58.67 years in AFAP families, respectively （P 〈 0.01）. Mean age of development of colorectal cancer was 42.23 in CFAP and 57.33 years old in AFAP （P 〈 0.01）. Mean of the earliest age at diagnosis of FAP was 29.95 years in the FAP families with a positive family history and 46.80 years in the FAP families with a negative family history （P 〈 0.01）. The ratio of extra-intestinal tumors to colorectal neoplasms was different in the two kinds of families with positive and negative family history （P 〈 0.01）. CONCLUSION： Additional use of ciclosporin will effectively improve to establish lymphocyte immortal cell lines with modified EB- transformation methods. In Chinese FAP, there was a high frequency of CHRPE, and a later age at diagnosis and a later age of development of colorectal cancer in AFAR And earlier age at diagnosis in FAP with positive family history was also found that will help to diagnose various kinds of FAP in Chinese.

Construction of a novel Shigella live-vector strain co-expressing CS3 and LTB/STm of enterotoxigenic E.coli

AIM: To construct and evaluate a polyvalent recombinant vaccine strain Shigella flexneri2a T32 against enterotoxigenic E.coli/(ETEC). METHODS: By using a host-plasmid balanced lethal system based on asd gene, a polyvalent recombinant strain was constructed to highly express CS3 and regularly express fusion enterotoxin of LIB subunit and mutant ST (LTB/STm) in a vaccine strain Shigella flexneri 2a T32 with specific deletion of asd gene. Fimbria CS3 was observed by immunofluorescence and electron microscopy assay. The security of LTB/STm was examined by ileal loop assay and suckling mouse assay. To evaluate this new candidate vaccine, it was compared with a previous vaccine strain in plasmid and protein level, growth assay and immunogenicity in Balb/c mice. RESULTS: The newly constructed vaccine expressed CS3 and grew better than the previously constructed vaccine except for the lower expression of LTB/STm. Serum IgG and mucosal IgA against CS3, LTB, ST, and host lipopolysaccharide (LPS) were produced after immunization of Balb/c mice by oral route with the new strain. The titers were not significantly different from the Balb/c mice with the previous strain. CONCLUSION: This novel candidate diarrheal vaccine can effectively induce serum and mucosal antibody responses against ETEC and Shigella.

Moxibustion inhibits interleukin-12 and tumor necrosis factor alpha and modulates intestinal flora in rat with ulcerative colitis

AIM: To investigate the effect of moxibustion on intestinal flora and release of interleukin-12 (IL-12) and tumor necrosis factor-α (TNF-α) from the colon in rat with ulcerative colitis (UC). METHODS: A rat model of UC was established by local stimulation of the intestine with supernatant from colonic contents harvested from human UC patients. A total of 40 male Sprague-Dawley rats were randomly divided into the following groups: normal (sham), model (UC), herb-partition moxibustion (HPM-treated), and positive control sulfasalazine (SA-treated). Rats treated with HPM received HPM at acupuncture points ST25 and RN6, once a day for 15 min, for a total of 8 d. Rats in the SA group were perfused with SA twice a day for 8 d. The colonic histopathology was observed by hematoxylin-eosin. The levels of intestinal flora, including Bifidobacterium, Lactobacillus, Escherichia coli (E. coli), and Bacteroides fragilis (B. fragilis), were tested by real-time quantitative polymerase chain reaction to detect bacterial 16S rRNA/DNA in order to determine DNA copy numbers of each specific species. Immunohistochemical assays were used to observe the expression of TNF-α and IL-12 in the rat colons. RESULTS: HPM treatment inhibited immunopathology in colonic tissues of UC rats; the general morphological score and the immunopathological score were significantly decreased in the HPM and SA groups compared with the model group [3.5 (2.0-4.0), 3.0 (1.5-3.5) vs 6.0 (5.5-7.0), P < 0.05 for the general morphological score, and 3.00 (2.00-3.50), 3.00 (2.50-3.50) vs 5.00 (4.50-5.50), P < 0.01 for the immunopathological score]. As measured by DNA copy number, we found that Bifidobacterium and Lactobacillus, which are associated with a healthy colon, were significantly higher in the HPM and SA groups than in the model group (1.395 ± 1.339, 1.461 ± 1.152 vs 0.045 ± 0.036, P < 0.01 for Bifidobacterium, and 0.395 ± 0.325, 0.851 ± 0.651 vs 0.0015 ± 0.0014, P < 0.01 for Lactobacillus). On the other hand, E. coli and B. fragilis, which are associated with an inflamed colon, were significantly lower in the HPM and SA groups than in the model group (0.244 ± 0.107, 0.628 ± 0.257 vs 1.691 ± 0.683, P < 0.01 for E. coli, and 0.351 ± 0.181, 0.416 ± 0.329 vs 1.285 ± 1.039, P < 0.01 for B. fragilis). The expression of TNF-α and IL-12 was decreased after HPM and SA treatment as compared to UC model alone (4970.81 ± 959.78, 6635.45 ± 1135.16 vs 12333.81 ± 680.79, P < 0.01 for TNF-α, and 5528.75 ± 1245.72, 7477.38 ± 1259.16 vs 12550.29 ± 1973.30, P < 0.01 for IL-12). CONCLUSION: HPM treatment can regulate intestinal flora and inhibit the expression of TNF-α and IL-12 in the colon tissues of UC rats, indicating that HPM can improve colonic immune response.

Soluble Expression and Rapid Quantification of GFP-hepA Fusion Protein in Recombinant Escherichia coli

To establish a rapid quantification method for heparinase I during its production in recombinant Escherichia coli, a translational fusion vector was constructed by fusing the N terminus of heparinase I to the C terminus of a green fluorescent protein mutant （GFPmutl）. As a result, not only was the functional recombinant expression of heparinase I in E. coli accomplished, but also a linear correlation was obtained between the GFP fluorescence intensity and heparinase I activity, allowing enzyme activity to be quantified rapidly during the fermentation.

Mutants of Escherichia coli heat-labile enterotoxin and cholera toxin as mucosal adjuvants

Mucosal vaccination has been getting more and more recognition because of its compliance and low risk of spreading infectious disease by contaminated syringes used in subcutaneous immunization. However, most vaccines are unable to induce immune responses when given mucosally, and require the use of strong adjuvant for effective delivery systems. Heat-labile enterotoxin (LT) and Cholera toxin(CT) are powerful mucosal adjuvants when co-administered with soluble antigens. But high toxicity hampers their use in humans. Thanks to the fine knowledge of the structure-function relationship of LT and CT, many nontoxic or low toxic mutants have been generated, part of them retain high adjuvanticity of mucosal immunization. Among these mutants, LTS63K, LTA72R, LTR192G and CTE29H, CTE112K have been widely investigated. LTS63K and CTE112K are fully non toxic, whereas LTA72R and CTE29H are low toxic, and LTR192G is nontoxic in vitro(it remains the same toxicity as wild type LT in vivo). These mutants are extremely active as mucosal adjuvants when co-administrated with a variety of antigens in different animal models. They will be investigated more widely and deeply in the future. Some of them will be tested soon in human bodies.

Efficient and Comprehensive Utilizatio℃n of Hemicellulose in the Corn Stover

Pretreatment of the corn stover powder by dilute sulphuric acid （solid-liquid ratio 1 ： 20） at 130 for 30 min was carried out with 89.09% of the hemicellulose removed. After filtration, the xylose-rich corn stover pretreatment liquid, whose fermentable sugar was from hemicellulose hydrolysis only, consisting of 81.16% xylose and 15.27% glucose, was used to cultivate genetic recombinant Escherichia coli BL21 with human-like collagen （HLC） expression enhanced by 50.00% and 63.71% xylose consumption.

肉用仔鸡免疫状态的形成

肉用仔鸡免疫状态的形成李有业摘译耿孝礼校过去，有些学者报道，肉用仔鸡的生命力和对各种病原性疾病的抵抗力，均取决于其免疫反应性状态。这种免疫反应性，在诸多情况下是决定于母体通过种蛋传给仔鸡的保护性因素。还有些学者报道，肉用仔鸡生后的初期，常发生伴有腹泻...

Expression of E. coli heat-labile enterotoxin B subunit in transgenic tobacco plants

Objective ： To construct plant transformation vector containing Escherichia coli heat-labile enterotoxin B subunit （LT-B） gene and generate LT-B transgenic tobacco plants. Methods： The LT-B coding sequence was amplified from pMMB68 by PCR, subcloned into middle vector pUCmT and binary vector pBI121 to obtain plant expression vector pBI-LTB, in which LT-B expression was controlled under the Cauliflower mosaic virus （CaMV） 35S promoter. The tobacco plants （Nicotiana tobacum L. Cuttivar Xanthi） were transformed by co-cultivating leaf discs method via Agrobacterium tumefaciens LBA4404 harboring the plant expression vector. The regenerated transgenic tobacco plants were selected by kanamycin and confirmed by PCR, Southern blot, Western blot and ELISA. Resuits： LT-B gene integrated in the tobacco genomic DNA and were expressed in 9 strains of transgenic tobacco plants. The yield was varied from 3. 36-10. 56 ng/mg total soluble tobacco leaf protein. Conclusion： The plant binary expression vector pBI-LTB was constructed successfully, and transgenic LT-B tobacco plants was generated, and confirmed by Southern blot. The protein LT-B expressed by engineered plants was identified by Western blot analysis and had the expected molecular weight of LT-B pentamer protein. This result is an important step close to developing an edible vaccine and supplying a mucasal immunoajuvant, which will contribute to the preven- tion of mucosaroute evading pathogen.

Gastric dysplasia may be an independent risk factor of an advanced colorectal neoplasm

AIM: To evaluate the relationship between gastric dysplasia and Helicobacter pylori (H pylori) and the occurrence of colorectal adenoma, and to defi ne the necessity for colonoscopy in patients with gastric dysplasia or H pylori infection.METHODS: From May 2005 to February 2008, 133 patients with established gastric dysplasia by gastroduo-denoscopy (EGD) were additionally investigated by colonoscopy. The authors compared results with those of 213 subjects who underwent both EGD and colonoscopy during the same period at the author’s Health Promotion Center as a control group. H pylori infection was evaluated in both the gastric dysplasia and control groups.RESULTS: The mean age of all 346 study subjects was 54.1 ± 10.5 years, and there were 258 (73%) men and 87 (27%) women. No signif icant difference was found between the H pylori positive and negative subjects in terms of the prevalence of colorectal adenoma and advanced colorectal adenoma (P = 0.261). Patients with gastric dysplasia showed no elevated risk of colorectal adenoma (OR = 0.910, 95% CI: 0.587-1.411, P = 0.738), but had a signif icantly higher risk of having advanced colorectal adenoma (OR = 3.382, 95% CI: 1.700-6.342, P = 0.000).CONCLUSION: The study emphasizes the need for colon surveillance in patients with gastric dysplasia, regardless of H pylori infection.

Identification of E. coli K12 chromosomal insertion sites of bacteriophage φ297

Objective:To identify the specific integration site of prophage φ297 in the host of E. coli K12 chromosome. Methods:Using molecular techniques such as Siebert PCR for walking from the int gene of prophage 297, which is similar to that of phage 933W to an unknown region in genomic DNA. A special adaptor is ligated to the ends of DNA fragments generated by digestion of genomic DNA with restriction enzymes that generates blunt ended fragments. Clone and subclone of PCR products, DNA sequencing and data analysis were used in this study. Results:The attL, attR and the core sequences were determined. The bacterial attachment site of phage φ297 was located in the yecE gene of E. coli K12. Conclusion:The phage φ297 integrates into the yecE gene of the E. coli K12 genome.

Primary Purification of Co-expressed Soluble and Insoluble Alpha-interferon 2b from Recombinant E. coli

Alpha-interferon 2b (IFN 2b) was produced both in soluble and insoluble forms from recombinant E. coli. The dissolution of the expressed IFN 2b in inclusion body was carried out and it was found that the optimal condition to dissolve the expressed protein was 7 mol稬1guanidinium salt solution at pH 3.0. The resultant solution was diluted 20 times using pH 6.0 buffer to refold the protein correctly. The cation exchange column was employed to purify both refolded and soluble IFN 2b. For soluble IFN sample, high IFN 2b recovery yield (92.1%) with 91.7% purity was obtained in the eluate. However, for refolded IFN sample, only 72.7% of IFN 2b was recovered with relatively low purity (56.8%) by cation exchange chromatography. Although the expression level of insoluble IFN was higher than that of co-expressed soluble IFN in this recombinant E. coli cells, the productivity of bioactive IFN 2b was higher with soluble expressed IFN after primary purification process. Soluble expression of foreign proteins in recombinant bacteria might be an alternative strategy for efficient production of heterogeneous pro-teins due to high bioactivity and simple downstream protein purification process.

Neutron （Magnetic Isotope） Catalysis for Example Isotopes 24,25,26Mg in Cells E. Coli

We offered the new theory of neutron （magnetic isotope） catalysis. For the first time it was shown that the number of neutrons in the atom, which have anomalous magnetic effect, have a great influence on the chemical properties. Our proposed theory of neutron （magnetic isotope） catalysis takes into account the influence of the magnetic field on the catalytic processes.

The Truncated Gene cfaD′ Positively Regulates CFA/Ⅰ Expression of Enterotoxigenic Escherichia coli

The gene cluster cfaABCED’ of enterotoxigenic Escherichia coli, encoding the fimbriae which is called colonization factor antigen located on a plasmid. It is positively regulated by cfaR, a member of the AraC family, and the cfaD’ gene region, which is located downstream of cfaE and is homologous to cfaR, had been described as a truncated cryptic gene. In the present study we observed that the CFA/ fimbriae subunit, cfaB, was expressed in lower amount by the cfaABCED’ clone pNTP513 in host E. coli HB101. The expression of CFA/ diminished by deletion of cfaD’ gene region from pNTP513, and was restored by acquisition of cfaD’ in trans. Furthermore, CFA/ expression by cfaD’ deletion mutant, the cfaABCE clone, was remarkably increased by the presence of cfaD’ in trans in a topoisomerase A deficient strain of E. coli DM800. These data suggest that cfaD’ region is a functional region of gene, that regulates the CFA/ expression with cfaR by unknown mechanism.

基于生物信息学分析从Streptomyces albofaciens JCM 4342中发现2,3-二羟基苯甲酸酯-L-丝氨酸脱水三聚体和二聚体天然产物

【背景】铁是细菌生长的基本元素,而三价铁在自然水环境中几乎无法溶解。细菌已经进化出产生各种铁载体的能力,以促进铁的吸收。对于链霉菌,其特有的铁载体是去铁胺,同时它们也可以产生其他结构的铁载体,如Ceolichelin、白霉素、肠杆菌素(Enterobactin)和Griseobactin。【目的】揭示链霉菌中铁载体生物合成基因簇(Biosynthetic Gene Clusters,BGCs)的分布特点和基因簇特征,并探索其所合成铁载体的化合物结构。【方法】利用生物信息学工具系统地分析308个具有全基因组序列信息的链霉菌中的铁载体生物合成基因簇,并用色谱和波谱方法分离和表征肠杆菌素相关天然产物。【结果】发现Streptomyces albofaciens JCM 4342和其他少数菌株同时含有一个缺少2,3-二羟基苯甲酸(2,3-DHB)生物合成基因的孤立的肠杆菌素生物合成基因簇和另外一个推测可合成Griseobactin的基因簇。从S.albofaciens JCM 4342发酵液中鉴定出4个肠杆菌素衍生的天然产物,包括链状2,3-二羟基苯甲酸酯-L-丝氨酸(2,3-DHBS)的三聚体和二聚体以及它们的脱水产物。【结论】2个基因簇间存在一种特别的协同生物合成机制。推测是Griseobactin基因簇负责合成2,3-DHB,而孤立的肠杆菌素基因簇编码的生物合成酶可夺取该底物,进而完成上述4种肠杆菌素衍生天然产物的生物合成。