Microplate Bioassay for Nisin in Foods, Based on Nisin-Induced Green Fluorescent Protein Fluorescence

A plasmid coding for the nisin two-component regulatory proteins, NisK and NisR, was constructed; in this plasmid a gfp gene (encoding the green fluorescent protein) was placed under control of the nisin-inducible nisF promoter. The plasmid was transformed into non-nisin-producing Lactococcus lactis strain MG1614. The new strain could sense extracellular nisin and transduce it to green fluorescent protein fluorescence. The amount of fluorescence was dependent on the nisin concentration, and it could be measured easily. By using this strain, an assay for quantification of nisin was developed. With this method it was possible to measure as little as 2.5 ng of pure nisin per ml in culture supernatant, 45 ng of nisin per ml in milk, 0.9 μg of nisin in cheese, and 1 μg of nisin per ml in salad dressings.     

Bioassay for nisin in milk, processed cheese, salad dressings, canned tomatoes, and liquid egg products

A sensitive nisin quantification bioassay was constructed, based on Lactococcus lactis chromosomally encoding the nisin regulatory proteins NisK and NisR and a plasmid with a green fluorescent protein (GFP) variant gfp(uv) gene under the control of the nisin-inducible nisA promoter. This strain, LAC275, was capable of transducing the signal from extracellular nisin into measurable GFPuv fluorescence through the NisRK signal transduction system. The LAC275 cells detected nisin concentrations of 10 pg/ml in culture supernatant, 0.2 ng/ml in milk, 3.6 ng/g in processed cheese, 1 ng/g in salad dressings and crushed, canned tomatoes, and 2 ng/g in liquid egg. This method was up to 1,000 times more sensitive than a previously described GFP-based nisin bioassay. This new assay made it possible to detect significantly smaller amounts of nisin than the presently most sensitive published nisin bioassay based on nisin-induced bioluminescence. The major advantage of this sensitivity was that foods could be extensively diluted prior to the assay, avoiding potential inhibitory and interfering substances present in most food products.     

Bioassay for Nisin in Milk, Processed Cheese, Salad Dressings, Canned Tomatoes, and Liquid Egg Products

A sensitive nisin quantification bioassay was constructed, based on Lactococcus lactis chromosomally encoding the nisin regulatory proteins NisK and NisR and a plasmid with a green fluorescent protein (GFP) variant gfp_uv gene under the control of the nisin-inducible nisA promoter. This strain, LAC275, was capable of transducing the signal from extracellular nisin into measurable GFPuv fluorescence through the NisRK signal transduction system. The LAC275 cells detected nisin concentrations of 10 pg/ml in culture supernatant, 0.2 ng/ml in milk, 3.6 ng/g in processed cheese, 1 ng/g in salad dressings and crushed, canned tomatoes, and 2 ng/g in liquid egg. This method was up to 1,000 times more sensitive than a previously described GFP-based nisin bioassay. This new assay made it possible to detect significantly smaller amounts of nisin than the presently most sensitive published nisin bioassay based on nisin-induced bioluminescence. The major advantage of this sensitivity was that foods could be extensively diluted prior to the assay, avoiding potential inhibitory and interfering substances present in most food products.     

A nisin bioassay based on bioluminescence.

A Lactococcus lactis subsp. lactis strain that can sense the bacteriocin nisin and transduce the signal into bioluminescence was constructed. By using this strain, a bioassay based on bioluminescence was developed for quantification of nisin, for detection of nisin in milk, and for identification of nisin-producing strains. As little as 0.0125 ng of nisin per ml was detected within 3 h by this bioluminescence assay. This detection limit was lower than in previously described methods.     

A Nisin Bioassay Based on Bioluminescence

A Lactococcus lactis subsp. lactis strain that can sense the bacteriocin nisin and transduce the signal into bioluminescence was constructed. By using this strain, a bioassay based on bioluminescence was developed for quantification of nisin, for detection of nisin in milk, and for identification of nisin-producing strains. As little as 0.0125 ng of nisin per ml was detected within 3 h by this bioluminescence assay. This detection limit was lower than in previously described methods.     

Optimization of fed-batch production of the model recombinant protein GFP in Lactococcus lactis

Optimization of recombinant protein production using lactic acid bacteria (LAB) remains an important obstacle on the road to realizing LAB as oral vaccine delivery vehicles. Despite this, there have been few published investigations to explore the higher limits of LAB recombinant protein expression in fed-batch fermentations. In this study, results from response surface experiments suggested an optimal set of conditions for expression of green fluorescent protein (GFP), a model recombinant protein, in bench-scale, fed-batch Lactococcus lactis IL1403 fermentations. The 48 4-L fed-batch fermentations in this set of experiments, along with preliminary studies, investigated the effects of pH, temperature, hemin concentration, concentration of the nisin inducer per cell, and time of induction. Cell densities in this data set ranged from 2.9 to 7.4 g/L and maximum GFP expression per cell ranged from 0.1 to 4.4 relative fluorescence units (RFU)/g. The optimal 4-L, fed-batch fermentation process found here yields growth and protein expression values that dramatically improve upon results from traditional test tube and flask processes. Relative to the traditional process, the experimental optimum conditions yield 4.9 times the cell density, 1.6 times the protein per cell mass, and 8 times the total protein concentration. Unexpectedly, experiments also revealed that the compound hemin, known previously to improve growth and survival of Lactococcus lactis (L. lactis), negatively impacted recombinant protein production when added in concentrations from 5 to 20 microg/mL with this strain. The improvement in protein expression over traditional processes demonstrated here is an important step toward commercial development of LAB for oral delivery of recombinant vaccines and therapeutic proteins.     

一种快捷可靠评价链霉菌噬菌体φC31整合酶功能的双荧光报告系统

在NIH3T3细胞中构建了一种链霉菌噬菌体φC31整合酶报告系统.该报告载体同时编码红色荧光蛋白和绿色荧光蛋白,与编码φC31整合酶的载体共转染可以反映φC31整合酶的活性.细胞中从红色荧光到绿色荧光的变化和百分比的变化可经流式细胞仪检出.随着转染中φC31整合酶表达载体的比例升高,表达绿色荧光的细胞比例上升.φbC31整合酶表达载体和报告系统载体比例在10:1时,可达最高约90%的红绿荧光转变率.这表明该φC31整合酶报告系统提供了一种在细胞中快捷可靠的评价φ31整合酶功能的方法.     

小鼠 LRRC 10腺病毒载体构建及其在心肌细胞中的表达

目的：构建含有小鼠Lrrc10（Leucine-rich Repeat Containing protein 10）基因的重组腺病毒表达载体。方法：设计小鼠Lrrc10特异性引物,以小鼠cDNA为模板,通过PCR扩增出mLrrc10的编码区,并引入HA标签蛋白和Sal Ι酶切位点。该片段经凝胶电泳纯化后插入pMD-18 T载体。测序后,用Sal Ι和Hind III酶切,将目的片段亚克隆至pAd-track-cmv穿梭载体中。用PmeΙ线性化后,用100 ng转化细菌BJ5183,在细菌内同源重组后得到 pAd-Lrrc10质粒。pAd-Lrrc10经PacⅠ线性化后用LipofectamineTM2000转染293A细胞,包装得到含Lrrc10基因的病毒重组子。将病毒重组子在293A细胞中扩增后,反复冻融得到滴度较高的含Lrrc10的病毒液。将收集的病毒液感染心肌细胞,绿色荧光观察 GFP、免疫印迹检测Lrrc10-HA蛋白的表达。结果：用病毒液感染原代心肌细胞,24小时后在荧光显微镜下可观察被感染的细胞发出绿色荧光,提取心肌细胞总蛋白,Western可检测到Lrrc10-HA融合蛋白的表达。结论：小鼠Lrrc10腺病毒载体构建成功,并可将编码Lrrc10-HA的目的片段导入心肌细胞中表达。     

Use of green fluorescent protein as molecular marker for taggingBacillus brevis in soil under the control of a novel constitutive promoter F1

A constitutive expression vector pHY300-Flgfp was constructed to test the function of promoter F1 subcloned from a rice epiphyte Bacillus brevis strain DX01. The DX01 cells harboring plasmid pHY300-F1gfp were detected to produce bright green fluorescence. Subsequently, the gfp-tagged B. brevis strain was released into the soil and its survival was investigated by PCR and the detection of green fluorescence. The spatial location of in situ gfp-tagged bacterial cells on the root surface of rice seedlings was visualized. All these results indicated that green fluorescent protein is an ideal molecular marker for the detection of the activities of promoter F1, and it is also a reliable probe to monitor specific B. brevis bacteria in the environment.     

Optimization of the green fluorescent protein (GFP) expression from a lactose-inducible promoter in Lactobacillus casei

An expression vector for Lactobacillus casei has been constructed containing the inducible lac promoter and the gene encoding ultraviolet visible green fluorescent protein (GFP(UV)) as reporter. Different conditions to grow L. casei were assayed and fluorescence as well as total protein synthesized were quantified. The maintenance of neutral pH had the greatest incidence on GFP(UV) expression, followed by aeration and a temperature of 30 degrees C. Environmental factors favoring GFP(UV) accumulation did not exactly correlate with those enhancing fluorescence. Therefore, oxygenation, by stirring the culture, had the greatest influence on the proportion of fluorescent protein, which is in accordance with the structural requirements of this protein. The highest yield obtained was 1.3 microg of GFP per mg of total protein, from which 55% was fluorescent.     

乳链菌肽细胞分子传感器的构建与应用

【背景】乳链菌肽主要是由乳酸乳球菌生产的一类多肽,对革兰氏阳性菌有抑菌作用,是目前联合国粮食及农业组织/世界卫生组织唯一批准使用的天然食品防腐剂。但是其产量低、缺乏简便高效的检测方法,限制了其研究和应用。【目的】构建一种可输出肉眼可见红色荧光的细胞分子传感器,以期能简单方便地检测样品中的乳链菌肽,同时应用该传感器筛选乳链菌肽生产菌株。【方法】用Golden-Gate克隆方法构建含乳链菌肽诱导启动子和下游红色荧光蛋白基因(两种)的载体,转入Lactococcus lactis中。用细胞传感器筛选可能的乳链菌肽生产菌株。【结果】构建的两种乳链菌肽细胞分子传感器都能对2?200 ng/mL乳链菌肽有灵敏的响应,可用于定量测定。两种传感器的最大荧光强度和表型也有所不同。利用细胞传感器确定了Lactococcus lactis ATCC 11454乳链菌肽的产生,同时排除了一个能产其他抗菌化合物的菌株。【结论】构建的细胞分子传感器能特异性地响应乳链菌肽,并能简单快速地筛选乳链菌肽菌株。     

Carbon dioxide and nisin act synergistically on Listeria monocytogenes

This paper examines the synergistic action of carbon dioxide and nisin on Listeria monocytogenes Scott A wild-type and nisin-resistant (Nis(r)) cells grown in broth at 4 degrees C. Carbon dioxide extended the lag phase and decreased the specific growth rate of both strains, but to a greater degree in the Nis(r) cells. Wild-type cells grown in 100% CO(2) were two to five times longer than cells grown in air. Nisin (2.5 microg/ml) did not decrease the viability of Nis(r) cells but for wild-type cells caused an immediate 2-log reduction of viability when they were grown in air and a 4-log reduction when they were grown in 100% CO(2). There was a quantifiable synergistic action between nisin and CO(2) in the wild-type strain. The MIC of nisin for the wild-type strain grown in the presence of 2.5 microg of nisin per ml increased from 3.1 to 12.5 microg/ml over 35 days, but this increase was markedly delayed for cultures in CO(2). This synergism between nisin and CO(2) was examined mechanistically by following the leakage of carboxyfluorescein (CF) from listerial liposomes. Carbon dioxide enhanced nisin-induced CF leakage, indicating that the synergistic action of CO(2) and nisin occurs at the cytoplasmic membrane. Liposomes made from cells grown in a CO(2) atmosphere were even more sensitive to nisin action. Liposomes made from cells grown at 4 degrees C were dramatically more nisin sensitive than were liposomes derived from cells grown at 30 degrees C. Cells grown in the presence of 100% CO(2) and those grown at 4 degrees C had a greater proportion of short-chain fatty acids. The synergistic action of nisin and CO(2) is consistent with a model where membrane fluidity plays a role in the efficiency of nisin action.     

Identification of Nisin-Producing Strains by Nisin-Controlled Gene Expression System

A specific method to identify nisin-producing strains was developed based on Nisin-Controlled gene Expression (NICE) vector pSec:Nuc. The plasmid pSec:Nuc was transformed into non-nisin-producing strain Lactococcus lactis NZ9000, a host commonly used for the NICE system. The generating strain L. lactis NZ9000/pSec:Nuc could sense extracellular inducer nisin and efficiently secrete a reporter protein Nuc, the staphylococcal nuclease (Nuc) into the medium. Instead of using purified nisin, the culture supernatants of nisin-producing strains were also used as inducers. Therefore, the NICE system could be used to identify nisin-producing strains. With this principle, 4 among 56 lactococci strains isolated from raw milk were identified as nisin producers. The results were further confirmed by polymerase chain reaction amplification with their genomic DNA as templates, and nucleotide sequencing revealed that three of them produced nisin A, and the others produced nisin Z. Those results made it possible to isolate and identify nisin-producing strains specifically and rapidly using NICE system.     

Construction of Bacillus thuringiensis wild-type S76 and Cry- derivatives expressing a green fluorescent protein: two potential marker organisms to study bacteria-plant interactions

Collectively, the species Bacillus thuringiensis, Bacillus cereus, and Bacillus anthracis represent microorganisms of high economic, medical, and biodefense importance. Although the genetic correlation and pathogenic characteristics have been extensively dissected, the ecological properties of these three species in their natural environments remain poorly understood. Thus, a tractable marker for detecting these bacteria under specific environmental and physiological conditions is a valuable tool. With this purpose, a plasmid (pAD43-25) carrying a functional gfp gene sequence (gfpmut3A) was introduced into the wild-type strain Bacillus thuringiensis subsp. kurstaki S76, which bears approximately 11 plasmids, allowing constitutive synthesis of green fluorescent protein (GFP) during vegetative growth (strain S76GFP+). Additionally, this vector was transferred to a plasmid-cured (Cry-) B. thuringiensis host. Bright green cells were detected by fluorescence microscopy in both recombinants by 2 h after inoculation in liquid medium and could be seen throughout the remaining cultivation time until complete sporulation was accomplished. For strain S76GFP+ protein profile and plasmid DNA analyses indicate, respectively, that this recombinant maintained Cry proteins expression and resident plasmid outline. Thus, in addition to the potential of strain S76GFP+ as a marker organism in bacteria-plant interaction studies, the production and stability of active GFPmut3a make this unique expression system a useful experimental model to study adaptive changes of host-plasmid as well as plasmid-plasmid relationships in a population of cells stressed by the production of a recombinant protein.     

Flow cytometric testing of green fluorescent protein-tagged Lactobacillus rhamnosus GG for response to defensins

Lactobacillus rhamnosus GG is of general interest as a probiotic. Although L. rhamnosus GG is often used in clinical trials, there are few genetic tools to further determine its mode of action or to develop it as a vehicle for heterologous gene expression in therapy. Therefore, we developed a reproducible, efficient electroporation procedure for L. rhamnosus GG. The best transformation efficiency obtained was 10(4) transformants per microg of DNA. We validated this protocol by tagging L. rhamnosus GG with green fluorescent protein (GFP) using the nisin-controlled expression (NICE) system. Parameters for overexpression were optimized, which allowed expression of gfp in L. rhamnosus GG upon induction with nisin. The GFP+ strain can be used to monitor the survival and behavior of L. rhamnosus GG in vivo. Moreover, implementation of the NICE system as a gene expression switch in L. rhamnosus GG opens up possibilities for improving and expanding the performance of this strain. The GFP-labeled strain was used to demonstrate that L. rhamnosus GG is sensitive to human beta-defensin-2 but not to human beta-defensin-1.     

Rescue and preliminary application of a recombinant newcastle disease virus expressing green fluorescent protein gene

Based on the complete genome sequence of Newcastle disease virus (NDV) ZJI strain, seven pairs of primers were designed to amplify a cDNA fragment for constructing the plasmid pNDV/ZJI, which contained the full-length cDNA of the NDV ZJI strain. The pNDV/ZJI, with three helper plasmids, pCIneoNP, pCIneoP and pCIneoL, were then cotransfected into BSR-T7/5 cells expressing T7 RNA polymerase. After inoculation of the transfected cell culture supernatant into embryonated chicken eggs from specific-pathogen-free (SPF) flock, an infectious NDV ZJI strain was successfully rescued. Green fluorescent protein (GFP) gene was amplified and inserted into the NDV full-length cDNA to generate a GFP-tagged recombinant plasmid pNDV/ZJIGFP. After cotransfection of the resultant plasmid and the three support plasmids into BSR-T7/5 cells, the recombinant NDV, NDV/ZJIGFP, was rescued. Specific green fluorescence was observed in BSR-T7/5 and chicken embryo fibroblast (CEF) cells 48h post-infection, indicating that the GFP gene was expressed at a relatively high level. NDV/ZJIGFP was inoculated into 10-day-old SPF chickens by oculonasal route. Four days post-infection, strong green fluorescence could be detected in the kidneys and tracheae, indicating that the recombinant GFP-tagged NDV could be a very useful tool for analysis of NDV dissemination and pathogenesis.     

毕赤酵母液滴微流控高通量筛选方法的建立与应用

巴斯德毕赤酵母是当前应用最为方便和广泛的外源蛋白表达系统之一,为了进一步提高其表达外源蛋白的能力,文中建立了基于液滴微流控的毕赤酵母高通量筛选方法,并以木聚糖酶融合荧光蛋白为例,筛选获得木聚糖酶表达和分泌能力提高的突变株。通过PCR扩增得到木聚糖酶xyn5基因和绿色荧光蛋白gfp基因融合片段,并克隆到毕赤酵母表达载体pPIC9K中构建出木聚糖酶融合绿色荧光蛋白的质粒pPIC9K-xyn5-gfp,电转化至毕赤酵母GS115中得到表达木聚糖酶和绿色荧光蛋白的毕赤酵母SG菌株。该菌株经过常压室温等离子体诱变后进行单细胞液滴包埋,液滴培养24h后进行微流控筛选,获得高表达木聚糖酶的突变菌株,进而用于下一轮的诱变突变库构建和筛选。以此类推,经过5轮液滴微流控筛选,获得一株高产菌株SG-m5,其木聚糖酶活为149.17U/mg,较出发菌株提升300%,分泌外源蛋白的能力较出发菌株提高160%。文中建立的毕赤酵母单细胞液滴微流控高通量筛选方法能达到每小时10万菌株的筛选通量,筛选百万级别的菌株库仅需10h,消耗荧光试剂体积100μL,对比传统的微孔板筛选方法降低试剂成本近百万倍,为高效、低成本筛选获得表达和分泌外源蛋白能力提高的毕赤酵母提供了一条新途径。     

Rescue and Preliminary Application of a Recombinant Newcastle Disease Virus Expressing Green Fluorescent Protein Gene

Based on the complete genome sequence of Newcastle disease virus (NDV) ZJI strain, seven pairs of primers were designed to amplify a cDNA fragment for constructing the plasmid pNDV/ZJI, which contained the full-length cDNA of the NDV ZJI strain. The pNDV/ZJI, with three helper plasmids, pCIneoNP, pCIneoP and pCIneoL, were then cotransfected into BSR-T7/5 cells expressing T7 RNA polymerase. After inoculation of the transfected cell culture supernatant into embryonated chicken eggs from specific-pathogen-free (SPF) flock, an infectious NDV ZJI strain was successfully rescued. Green fluorescent protein (GFP) gene was amplified and inserted into the NDV full-length cDNA to generate a GFP-tagged recombinant plasmid pNDV/ZJIGFP. After cotransfection of the resultant plasmid and the three support plasmids into BSR-T7/5 cells, the recombinant NDV, NDV/ZJIGFP, was rescued. Specific green fluorescence was observed in BSR-T7/5 and chicken embryo fibroblast (CEF) cells 48h post-infection, indicating that the GFP gene was expressed at a relatively high level. NDV/ZJIGFP was inoculated into 10-day-old SPF chickens by oculonasal route. Four days post-infection, strong green fluorescence could be detected in the kidneys and tracheae, indicating that the recombinant GFP-tagged NDV could be a very useful tool for analysis of NDV dissemination and pathogenesis.     

糖基化磷脂酰肌醇锚定型EGFP真核表达质粒的构建及表达

构建与增强型绿色荧光蛋白基因相连的糖基化磷脂酰肌醇(glycosyl phosphatidylinositol,GPI)序列的真核表达质粒,并检测其在A549细胞中的表达.分离人外周血淋巴细胞,提取总RNA,以RT-PCR法扩增CD24基因的243 bp GPI锚定序列,双酶切后定向克隆入pEGFP-C1质粒中,构建并鉴定pEGFP-C1-GPI质粒.经脂质体介导转染A549细胞后,在荧光显微镜下观察目的蛋白在真核细胞内的表达情况.经酶切和测序鉴定证实,所克隆的CD24 GPI序列正确,荧光显微镜观察pEGFP-C1-GPI质粒转染A549细胞可见围绕细胞膜的强绿色荧光,而对照pEGFP-C1质粒转染A549细胞仅见胞内均匀荧光.成功构建与EGFP相连的GPI真核表达质粒,且能在A549细胞膜上锚定表达EGFP-GPI融合蛋白,为构建锚定表达型肿瘤疫苗奠定基础.