pBT2葡萄球菌表达质粒

基本信息

复制子:	ori Ec
终止子:	T1
质粒分类:	金黄色葡萄球菌质粒
质粒大小:	6.97kb
原核抗性:	氨苄青霉素Ampicillin
筛选标记:	氯霉素Chloramphenicol
克隆菌株:	DH5α
培养条件:	30℃，有氧，LB
表达宿主:	金黄色葡萄球菌等革兰氏阳性菌
备注:	金黄色葡萄球菌基因敲除载体

质粒简介

该载体是大肠杆菌-金黄色葡萄球菌穿梭载体，低拷贝，在大肠中抗性为氨苄，在金葡菌中抗性为氯霉素。该质粒具有温度敏感性。


相关的配套菌株为RN4220金黄色葡萄球菌, 相关的载体为pKOR1载体。
Protocols for gene deletion in Staphylococcus aureus   Nov. 1, 2007

Preparation of competent Staphylococcus aureus cells
1. Remove Staphylococcus aureus cells from the vial with a sterile toothpick or inoculation loop, and streak it out on LB agar.
2. Incubate at 37°C overnight.
3. Pick a single colony and inoculate it in 5-10 ml of LB. Grow at 37°C overnight.
4. Add 1 ml overnight culture to 100 ml LB medium in a 500 ml flask, and shake at 37°C until an OD600 of 0.4 is reached (approximately 90–120 min).
5. Cool the culture on ice for 5 min, and transfer the culture to a sterile, round-bottom centrifuge tube.
6. Collect the cells by centrifugation at low speed (5-10 min, 2500 x g, 4°C).
7. Discard the supernatant carefully. Always keep the cells on ice.
8. Resuspend the cells gently in 0.5 M sucrose (10-15 ml for a 100 ml culture) at 4°C and keep the suspension on ice for additional 5 min.
9. Collect the cells by centrifugation (5 min, 2500 x g, 4°C).
10. Discard the supernatant carefully. Repeat step 8 and 9.
11. Resuspend the cells carefully in 1 ml ice-cold 0.5 M sucrose and keep the suspension on ice for 15 min.
12. Prepare aliquots of 100–200 μl in sterile microcentrifuge tubes and freeze in liquid nitrogen. Store the competent cells at –70°C.

Construction of deletion vector
1. PCR amplify a 400 bp fragment upstream and a 400 bp fragment downstream of the target gene.
2. PCR amplify the ermB (Em resistance marker) from pECI.
3. Digest the three fragments, ligate, and PCR amplify the ligated product.
4. Purify the PCR product, double digest it, and ligate it into pBT2.
5. Transform the ligated product into E. coli.
6. Pick clones that can grow on the LB plate containing Em (100 mg/ml), purify the plasmid and digest it.
7. If the result of enzyme digestion is correct, get further confirmation by sequencing. 　

Procedure for electroporation
1. Mix 500 ng of plasmid DNA with electrocompetent Staphylococcus aureus cells and place them in a Gene Pulser cuvette with a 0.2 cm electrode gap.
2. The settings for electroporation are as follows: Voltage, 2.5 kV; capacitor, 50 μF; resistance, 200 ohms.
3. After electroporation the cells are immediately placed in 400 μl of TSB with shaking (200-220 rpm, 37°C) for 1h. Plate the cells on Em-containing medium and incubate at 37°C.

Modify deletion vector
1. Before transform the plasmid into Staphylococcus aureus NCTC8325, the plasmid should be transformed into Staphylococcus aureus RN4220.
2. Pick clones, after overnight growth, extract the plasmid.
3. Then the plasmid is modified and can’t be digested by restriction enzyme system of NCTC8325.

Deletion of target gene
1. Extract plasmid from RN4220, transform it into NCTC8325.
2. Pick up clones, incubate in B-medium, 30°C, grow to late-stationary phase, then change temperature to 40°C, and grow overnight.
3. 1: 100 dilute the culture into fresh B-medium, and grow overnight.
4. Follow step 3, spread 1 μl overnight culture (diluted into 100 μl) on agar plate (containing Em 2.5 mg/ml). Screen clones which are Em-resistant and Cm-sensitive.
5. Repeat step 4 until Em-resistant, Cm-sensitive clones are found.
6. Extract genome DNA of these clones, use PCR for further check.
 

质粒图谱

pBT2葡萄球菌表达质粒使用说明：
    
     1、收到质粒干粉后请先5000rpm离心1min，再加入20μl无菌水溶解质粒，室温放置1min；
     2、从-80℃冰箱中取出相应的感受态，置于冰盒上解冻，并做好标记；
     3、取2μl质粒加至100μl感受态中，冰浴30min；
     4、42℃热激90s，再冰浴2min；
     5、加入900μl无抗的LB液体培养基，180rpm震荡培养45min；
     6、6000rpm离心5min，仅留100ul上清混匀菌体沉淀；
     7、混匀后的菌液加至对应抗性的LB平板上，倒入适量玻璃珠，涂匀液体；
     8、将平板正向培养1h，再倒置培养12h~16h；
     9、挑取单克隆菌落至对应抗性的LB液体培养基中，震荡培养12h~16h，根据实验需要提取质粒。
 
pBT2葡萄球菌表达质粒注意事项：
 
      1、如果您收到的是甘油菌种，请先四区划线，挑取单克隆培养。
      2、如果第二天转化平板长的过多，请将质粒按比例稀释后再转化。