BioVector? pDG364 Bacillus subtilis Integration Vector / pDG364 枯草芽孢桿菌染色體整合型質(zhì)粒載體

一 產(chǎn)品基本信息與分子生物學(xué)背景

• 載體名稱：pDG364。

• 載體分類：枯草芽孢桿菌（Bacillus subtilis）整合型/穿梭型克隆載體。

• 質(zhì)粒大小：約 6.0 kb。

• 骨架源起與設(shè)計背景：

  pDG364 是研究革蘭氏陽性模式細(xì)菌——枯草芽孢桿菌（B. subtilis）基因表達(dá)與遺傳調(diào)控極為經(jīng)典的染色體整合型（Integration vector）穿梭質(zhì)粒。該載體由著名的 Bacillus 遺傳學(xué)專家開發(fā)，設(shè)計初衷是為了克服質(zhì)粒在枯草芽孢桿菌中復(fù)制不穩(wěn)定性（Segregational instability）的致命缺陷。pDG364 屬于非復(fù)制型整合載體（Non-replicative integration vector）。它含有大腸桿菌復(fù)制子，但不含有能在枯草芽孢桿菌內(nèi)自主復(fù)制的 Ori 序列。因此，當(dāng)其通過轉(zhuǎn)化進(jìn)入枯草芽孢桿菌后，必須通過同源重組的方式“逼迫”自身攜帶的表達(dá)元件完整地嵌入到枯草芽孢桿菌的染色體基因組中，從而實現(xiàn)外源基因極其穩(wěn)定的、單拷貝的永久表達(dá)。

• 核心順式作用元件與圖譜特征：

  • $amyE$ 同源重組側(cè)翼序列（$amyE$ Flanking Homology Regions）：這是 pDG364 的核心構(gòu)造。多克隆位點(diǎn)（MCS）和選擇抗性標(biāo)記被完整夾在 $amyE$-front（$amyE$ 基因的前端片段）與 $amyE$-back（$amyE$ 基因的后端片段）之間。通過這兩段長約數(shù)幾百堿基對的同源序列，質(zhì)粒在進(jìn)入枯草芽孢桿菌后，會與宿主染色體上的 $amyE$（編碼 $\alpha$-淀粉酶）位點(diǎn)發(fā)生雙交換同源重組（Double-crossover homologous recombination）。

  • 多克隆位點(diǎn)（MCS）：位于重組夾層內(nèi)，提供獨(dú)特的限制性內(nèi)切酶切位點(diǎn)（如 BamHI, SalI, PstI, EcoRI 等），便于嵌入目標(biāo)啟動子、報告基因或目標(biāo)蛋白編碼序列。

  • 雙選擇抗性標(biāo)記（Dual Selection Markers）：

    1. 氨芐青霉素抗性基因（$Amp^R$ / bla）：位于重組區(qū)段之外的骨架上，專門用于在大腸桿菌（E. coli）中擴(kuò)增克隆時進(jìn)行選擇。

    2. 氯霉素抗性基因（$Cm^R$ / cat）：位于 $amyE$ 重組夾層內(nèi)部。當(dāng)下游的雙交換整合成功發(fā)生后，該基因會隨目標(biāo)片段一同嵌入枯草芽孢桿菌染色體中，作為枯草芽孢桿菌陽性整合克隆的篩選指征。

  • 原核復(fù)制子：含有高拷貝的 pUC ori，僅在大腸桿菌內(nèi)起作用，確?？稍?E. coli 中進(jìn)行常規(guī)、高效的質(zhì)粒分子克隆和大量抽提。

二 核心科研價值與遺傳學(xué)轉(zhuǎn)化應(yīng)用

pDG364 質(zhì)粒在芽孢桿菌基因工程、合成生物學(xué)及工業(yè)酶制劑開發(fā)中具有核心立足點(diǎn)：

1. 外源基因的超高穩(wěn)定性單拷貝整合表達(dá)：

   在枯草芽孢桿菌中，普通游離型質(zhì)粒極易在沒有抗生素壓力的情況下發(fā)生丟失（Plasmid loss），不適合大規(guī)模工業(yè)發(fā)酵。利用 pDG364 將目標(biāo)基因整合至染色體后，外源片段將伴隨細(xì)菌基因組的復(fù)制而復(fù)制，在不加任何抗生素的復(fù)雜發(fā)酵液中亦能實現(xiàn) 100% 穩(wěn)定遺傳。

2. 淀粉酶失活表型打靶與順式雙交換驗證（$amyE$ Blasting Assay）：

   重組片段整合進(jìn)染色體后，會徹底破壞宿主原有的 $amyE$ 基因結(jié)構(gòu)，導(dǎo)致枯草芽孢桿菌完全喪失分泌 $\alpha$-淀粉酶的能力?？蒲腥藛T可通過經(jīng)典的“淀粉平板碘液染色法”（淀粉酶轉(zhuǎn)陰實驗），極其直觀地排除由于單交換（Single-crossover）導(dǎo)致的質(zhì)粒整株嵌入，精準(zhǔn)鎖定真正的雙交換染色體無痕整合株。

3. 枯草芽孢桿菌啟動子強(qiáng)度調(diào)控與功能基因打靶：

   常用于在 $amyE$ 位點(diǎn)引入不同的誘導(dǎo)型啟動子（如 $P_{spac}$、$P_{xyl}$）或報告基因（如 $lacZ$、$gfp$），用來在完全平行的染色體背景下，精確定量測定中樞基因網(wǎng)絡(luò)在芽孢形成（Sporulation）和感受態(tài)（Competence）發(fā)育階段的生化時空驅(qū)動特性。

三 實驗室大腸桿菌擴(kuò)增、枯草轉(zhuǎn)導(dǎo)、表型篩選標(biāo)準(zhǔn)步驟

1. 質(zhì)粒在大腸桿菌（E. coli）中的克隆與純化

• 常規(guī)轉(zhuǎn)化：將常規(guī)構(gòu)建好的 pDG364 重組質(zhì)粒通過熱擊法轉(zhuǎn)化入大腸桿菌（如 DH5$\alpha$ 或 TOP10）感受態(tài)細(xì)胞中。

• 平板篩選：涂布于含有 100 $\mu$g/mL 氨芐青霉素（Ampicillin）的 LB 固體平板上，37 攝氏度培養(yǎng)過夜。

• 質(zhì)粒抽提：挑取陽性單菌落進(jìn)行液體擴(kuò)增，使用標(biāo)準(zhǔn)堿裂解法質(zhì)粒抽提試劑盒回收高濃度的環(huán)狀重組質(zhì)粒，測定純度（$OD_{260}/OD_{280} = 1.8-1.9$），作為轉(zhuǎn)化枯草芽孢桿菌的供體底盤。（注：整合至枯草染色體需要完整的雙鏈環(huán)狀質(zhì)粒或經(jīng)特定酶切切出含有重組夾層的線性片段）。

2. 枯草芽孢桿菌感受態(tài)轉(zhuǎn)化操作（兩階段兩步法，以經(jīng)典 168 株為例）

由于 pDG364 無法在枯草體內(nèi)自主復(fù)制，轉(zhuǎn)化時對 DNA 的投入量及感受態(tài)效率要求較高。

1. 配制芽孢桿菌生長培養(yǎng)基：提前制備 SPI 培養(yǎng)基（富含高氨基酸與糖）與 SPII 培養(yǎng)基（限制性無機(jī)鹽鹽度培養(yǎng)基，用于誘導(dǎo)感受態(tài)啟動）。

2. 兩階段培養(yǎng)：

   • 將枯草芽孢桿菌宿主（如 B. subtilis 168）接種于 SPI 培養(yǎng)基中，37 攝氏度劇烈振蕩培養(yǎng)至對數(shù)生長末期（$\sim T_0$ 階段，通?？梢娚L曲線趨于平緩）。

   • 按 1:10 稀釋體積轉(zhuǎn)接至預(yù)熱的 SPII 培養(yǎng)基中，37 攝氏度、低速溫和振蕩培養(yǎng) 1.5 - 2 小時，此時細(xì)菌進(jìn)入最佳感受態(tài)（Competence）窗口。

3. 質(zhì)粒轉(zhuǎn)導(dǎo)：吸取 0.5 - 1.0 $\mu$L 處于高濃度狀態(tài)（$\ge 500\text{ ng}$）的 pDG364 重組質(zhì)粒 DNA，加入到 100 - 200 $\mu$L 的枯草感受態(tài)細(xì)胞懸液中。

4. 孵育復(fù)蘇：在 37 攝氏度搖床中以 100 rpm 溫和搖育復(fù)蘇 60 - 90 分鐘，允許同源重組酶系統(tǒng)（RecA 通路）有足夠的時間在染色體位點(diǎn)完成鏈置換與雙交換剪切。

3. 枯草整合株的雙重表型篩選與確證

1. 抗生素耐藥初篩：

   將復(fù)蘇后的枯草菌液以 10,000 rpm 離心 1 分鐘，棄部分上清。重懸后均勻涂布于含有 5 $\mu$g/mL 氯霉素（Chloramphenicol）的 LB 固體平板上。置于 37 攝氏度培養(yǎng) 18 - 24 小時。（注：只有成功發(fā)生染色體同源重組嵌入、或者極少數(shù)發(fā)生質(zhì)粒單交換非特異嵌入的菌株才能在此濃度氯霉素平板上存活）。

2. $\alpha$-淀粉酶失活（AmyE陰性）表型確證（核心質(zhì)控點(diǎn)）：

   • 配制含有 1% 可溶性淀粉（Soluble Starch）的 LB 固體篩選平板。

   • 用無菌牙簽挑取氯霉素平板上長出的枯草單菌落，點(diǎn)陣式接種到淀粉平板上，同時接種一株未轉(zhuǎn)化的野生型枯草 168 作為陽性對照。37 攝氏度孵育過夜。

   • 碘液染色顯色：向長有菌落的淀粉平板表面傾倒適量 盧戈氏碘液（Lugol's iodine solution），使其完全浸沒培養(yǎng)基表面，靜置 1 - 2 分鐘后倒掉。

   • 結(jié)果判定：

     • 野生型對照（或未成功雙交換整合的假陽性株）：由于能合成并向胞外分泌淀粉酶，會將菌落周圍的淀粉水解。碘液染色后，菌落周圍會自發(fā)顯現(xiàn)出一圈高度清晰、透明的“褪色透明圈（Halos）”。

     • 正確的 pDG364 雙交換染色體整合株：由于 $amyE$ 基因已被重組片段從中徹底截斷破壞，無法產(chǎn)生淀粉酶。碘液染色后，菌落周圍完全沒有透明圈，整體呈現(xiàn)均勻致密的藍(lán)黑色或紫褐色，即表現(xiàn)為 $AmyE^-$ 表型。

3. 分子確證：挑選表現(xiàn)為 $Cm^R$ 且 $AmyE^-$ 的核心克隆，提取枯草基因組（Genomic DNA），設(shè)計跨越 $amyE$ 側(cè)翼邊界的引物進(jìn)行 PCR 測序驗證，鎖定完美的單拷貝染色體工程整株。

Part 2 English Section

I General Information and Cell Biological Background

• Vector Name: pDG364.

• Vector Classification: Chromosomal integration / shuttle cloning vector designed for Bacillus subtilis.

• Plasmid Size Scale: Approximately 6.0 kb.

• Backbone Origin and Engineering Background:

  The pDG364 vector is a widely used insertion chassis configured to evaluate gene expression landscapes and transcriptional circuitries within the Gram-positive model organism Bacillus subtilis. Developed by prominent Bacillus geneticists, it was engineered to circumvent segregational and structural plasmid instability inherent to autonomous replication vectors in Bacillus species.

  Crucially, pSP364 operates as a non-replicative integration vector. While it possesses a standard E. coli replication origin, it lacks a functional origin of replication (Ori) configured for Bacillus subtilis hosts. Consequently, upon transformation into a B. subtilis recipient, the plasmid cannot persist episomally; it is forced to undergo homologous recombination with the host genome to rescue its selection cargo, resulting in highly stable, single-copy, permanent genomic integration of target cassettes.

• Core Cis-Acting Elements and Map Characterization:

  • $amyE$ Homology Flanking Insertion Segments: This region represents the functional machinery of pDG364. The Multiple Cloning Site (MCS) and internal selection markers are locked between $amyE$-front and $amyE$-back sequences. These homologous flanking sequences guide a precise double-crossover homologous recombination event targeting the endogenous chromosomal $amyE$ locus (encoding native extracellular $\alpha$-amylase).

  • Multiple Cloning Site (MCS): Nestled inside the recombination cassette, it provides discrete, unique restriction endonuclease cutting boundaries (e.g., BamHI, SalI, PstI, EcoRI) to anchor external promoters, reporter segments, or open reading frames.

  • Dual Selective Antibiotic Elements:

    1. Ampicillin Resistance Gene ($Amp^R$ / bla): Located externally to the $amyE$ homology locus on the plasmid backbone; serves exclusively as a selectable marker during standard E. coli molecular cloning routines.

    2. Chloramphenicol Resistance Gene ($Cm^R$ / cat): Embedded within the internal $amyE$ recombination boundaries. Following a successful double-crossover integration sequence, this cassette embeds into the B. subtilis chromosome, serving as a reliable index for identifying positive B. subtilis clones.

  • Prokaryotic Replicon: Features a standard high-copy pUC ori, functioning exclusively inside E. coli hosts to permit efficient plasmid amplification and recovery.

II Strategic Research Value and Genetic Applications

The pDG364 plasmid is a fundamental tool for Bacillus-based genetic engineering, synthetic biology, and industrial enzyme production:

1. Ultra-Stable Singe-Copy Genomic Expression Matrix:

   Standard episomal vectors in B. subtilis face significant plasmid loss when cultured over extended generations without continuous antibiotic selection pressure, rendering them unsuitable for industrial fermentation scales. Integrating target expressions via pDG364 into the host chromosome ensures that the target sequence replicates alongside the host genome, providing 100% inheritance stability in complex fermenter environments without requiring antibiotics.

2. Definitive Verification of Double-Crossover Recombination via Amylase Disruption:

   Successful target insertion disrupts the endogenous chromosomal $amyE$ gene framework, abolishing the host's ability to synthesize and secrete active $\alpha$-amylase. Utilizing a simple starch-iodine assay ($AmyE$ phenotype test), investigators can exclude false-positive single-crossover integration events and confirm correct double-crossover single-copy genomic insertion.

3. Evaluating Promoters and Mapping Temporal Gene Networks:

   pDG364 is standardly utilized to introduce custom inducible promoter configurations (e.g., $P_{spac}$, $P_{xyl}$) or visual reporters ($lacZ$, $gfp$) directly into the $amyE$ target domain. This provides a clean genomic environment to measure the precise temporal and spatial expression kinetics of regulatory networks during the complex life cycles of spore development (sporulation) and competence development.

III Laboratory E. coli Propagation, Bacillus Transformation, and Phenotypic Screening Protocols

1. Vector Propagation and Purification inside Escherichia coli

• Transformation Sequence: Deliver the engineered recombinant pDG364 plasmid configuration into standard competent E. coli cells (such as DH5$\alpha$ or TOP10) via standard heat-shock parameters.

• Selection Parameters: Plate the transformation mixture onto solid LB agar matrices supplemented with 100 $\mu$g/mL Ampicillin and cultivate at 37 °C overnight.

• Plasmid Harvesting: Harvest verified single colonies into selective liquid broth and extract plasmid constructs via standard alkaline-lysis kits. Ensure purity checks align with clear parameters ($OD_{260}/OD_{280} = 1.8-1.9$) to provide high-quality template stocks for downstream Bacillus delivery. Note: Successful double-crossover chromosomal entry requires clean circular plasmids or linearized fractions encompassing intact flanking regions.

2. Bacillus subtilis Competence Transduction (Classic Two-Step Method)

Because pDG364 cannot propagate autonomously in B. subtilis, high DNA mass input combined with optimized competence preparation protocols is required.

1. Reagent Media Setup: Prepare sterile SPI growth media (nutrient-rich, amino acid-supplemented formulation) and SPII starvation media (low-salt, mineral-restricted matrix to force competence machinery activation).

2. Two-Phase Biomass Cultivation:

   • Inoculate the target B. subtilis recipient strain (e.g., standard B. subtilis 168) into pre-warmed SPI growth medium. Agitate vigorously at 37 °C until the biomass transitions into late log phase ($\sim T_0$ point, marked by a stabilization of growth kinetics).

   • Transfer this culture at a 1:10 dilution into pre-warmed SPII starvation media. Reduce agitation speeds slightly and cultivate at 37 °C for 1.5 - 2 hours to optimize the transformation window.

3. Plasmid Interfacing: Add 0.5 - 1.0 $\mu$L of concentrated, high-purity pDG364 recombinant vector DNA ($\ge 500\text{ ng}$) into 100 - 200 $\mu$L of the prepared competent Bacillus cell suspension.

4. Outgrowth / Recombination Phase: Incubate the transformation mixture at 37 °C with gentle shaking at 100 rpm for 60 - 90 minutes. This outgrowth interval allows the endogenous recombinase network (RecA pathways) sufficient time to perform strand exchange and execute the required double-crossover alignment.

3. Dual Phenotypic Identification and Chromosomal Screening Verification

1. Primary Antibiotic Selection Gate:

   Centrifuge the recovered Bacillus outgrowth mixture at 10,000 rpm for 1 minute, decant a portion of the supernatant, resuspend the pellet, and plate the solution uniformly onto solid LB agar plates supplemented with 5 $\mu$g/mL Chloramphenicol. Incubate at 37 °C for 18 - 24 hours. Note: Only cells that have integrated the chloramphenicol resistance gene into their chromosome via homologous recombination—or rare single-crossover events—will form colonies.

2. Confirmation of $\alpha$-Amylase Inactivation ($AmyE^-$ Phenotype Validation):

   • Prepare a fresh set of solid selective LB agar plates enriched with 1% soluble starch.

   • Using a sterile toothpick, patch chloramphenicol-resistant colonies onto the starch plate in a grid pattern. Ensure a wild-type untransformed strain (e.g., B. subtilis 168) is patched on the same plate to serve as a positive control for amylase activity. Incubate at 37 °C overnight.

   • Lugol's Iodine Developing Assay: Flooding the plate surface with an appropriate volume of Lugol's iodine solution until the solid medium is completely submerged. Allow it to react for 1 - 2 minutes, then discard the excess liquid.

   • Phenotypic Result Determination:

     • Wild-type Reference (or false-positive single-crossover clones): Retain an intact $amyE$ gene structure and continue to secrete functional amylase, which hydrolyzes surrounding starch molecules. Upon iodine development, these colonies will be surrounded by a sharp, clear, colorless halo.

     • Correct pDG364 Double-Crossover Recombinants: The endogenous $amyE$ open reading frame is disrupted by the integration cassette, abolishing amylase production. Upon iodine development, these colonies exhibit no clear zone, with the surrounding agar staining a uniform dark blue-black or deep purple color ($AmyE^-$ phenotype).

3. Molecular Architecture Validation: Harvest verified $Cm^R$ and $AmyE^-$ candidate clones, isolate genomic DNA (gDNA), and run PCR verification across the integration boundaries to confirm single-copy genomic insertion before establishing working cell banks.

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