Tn5—Mob转座系统对紫云英根瘤菌SR72的诱变和诱动作用

通过接合作用将携带有转座子 Tn5—Mob 的“自杀”性载体质粒 pSUP5011引入紫云英根瘤菌 SR72,得到卡那霉素抗性(Km~r)菌落的频率为6.99×10~(-6),测得受体菌的 Km~r 自发突变频率<10~(-8)。从对1071个 Km~r 突变体进行的植物砂培结瘤试验中筛选出结瘤不固氮(Nod~ ,Fix~-)突变株17个,不结瘤(Nod~-)突变株4个。另外,还从近3000个 Km~r 突变体中选出腺苷营养缺陷型突变株3个。通过 Tn5探针进行的菌落原位杂交试验证明:这21个共生固氮突变株中均含有 Tn5序列,进一步通过接合作用将协助质粒 RP4—4(Tc~r)引入 Nod~ ,Fix~ 突变株,获得了含有 Tn5—Mob 和 RP4—4的新突变株 SR72ZR(Km~r,Tc~r),但试图通过它们的协同作用将SR72中的大质粒诱动转移到根癌农杆菌 A136的试验未获成功.     

六株成团肠杆菌 (Enterobacteragglomerans)接合子的分子生物学分析

对 6株成团肠杆菌 (Enterobacteragglomerans)接合子的分子生物学进行了分析 .6株菌与nifHDK基因有杂交 .菌株总DNA经BamHⅠ酶切后与pEA9 DNA进行Southern杂交 ,只有 2株菌具有完整的质粒DNA ,其余菌株质粒DNA发生了 15 3～ 137 7kb不同程度的缺失 .用切割位点较少的限制性内切酶XbaⅠ酶切 6株菌的总DNA ,经脉冲场凝胶电泳 (PFGE)后用pEA9 DNA为探针进行Southern杂交 ,每株菌的pEA9 DNA明显大于用BamHⅠ酶切后的杂交结果 ,表明质粒与染色体发生了整合 .转座子Tn5或插入序列IS 12 2 2和IS 12 71可能参与质粒与染色体的整合过程 .     

由质粒介导的浑球红假单胞菌的染色体基因转移

通过接合转移,质粒pR751：：813、pACYCl84：：Tn5和RP4：：Mu从大肠杆菌引入浑球红假单胞菌。以质粒pR751：：813和RPI：：TnS01为介导的染色体转移,构威了一条染色体基因连锁图,并确定了包括半胱氨酸和胞嘧啶在内的六个遗传标记的相对位置。决定卡那霉素抗性的转座子Tn5以每供体}．3×10一’频率从大肠杆菌转入浑球红假单胞菌。约1．5％的“m‘分离物是营养缺陷型。形成的半胱氨酸变种是稳定的,回复突变频率约为4×10-10。转座子插入诱变产生的变种可用于遗传分析研究。     

豌豆根瘤菌共生基因pJB5JI与华癸中生根瘤菌7653R共生质粒的相互关系

华癸中生根瘤菌(Mesorhizobium huakuii)7653R是分离自我国南方水稻田的一株根瘤菌,含有2个内源质粒:p7653Ra和p7653Rb,其中7653Rb是共生质粒.通过Tn5-sacB的插入方法来消除质粒,获得7653Rb消除的突变株7653RD.将豌豆根瘤菌T83K3的共生质粒pJB5JI导入7653R和7653RD中,盆栽结果表明含有pJB5JI的转移接合子7653R-197的竞争结瘤能力和共生固氮能力均高于7653R.pJB5JI不能恢复7653RD在紫云英上的结瘤能力.含有pJB5JI的7653RD可以在豌豆上结无效瘤,表明pJB5JI可以在7653R的染色体背景下表达其功能.对转移接合子中的质粒稳定性进行检测,结果表明pJB5JI在人工传代的情况下可以稳定存在,但经过共生之后发生了遗传分离,对转移接合子和出发菌株及分离菌株进行kan基因的PCR扩增,除了受体菌外其他菌株都可得到PCR产物,由此推测,pJB5JI可能部分或全部整合到了受体菌的染色体基因组中.     

转座因子在肺炎链球菌耐药进化中的作用

要肺炎链球菌的耐药决定子由染色体上的转座因子携带,与耐药相关的转座因子和转移的主要方式有：①接合转座子：携带erm(B)、tet(M)和aphA-3等的Tn916-Tn1545家族,通过接合转移;②缺陷转座子：携带mef基因及ABC外排系统的Tn1207．1和mega插入元件,可转化到敏感菌株引起耐药;③复合转座子：由mega插入元件与Tn916整合产生的Tn2009,以转化方式转移。肺炎链球菌通过转座因子获得并传播耐药基因,在其耐药进化中起重要作用。     

转座子Tn917诱变的炭疽杆菌芽孢形成缺陷株的筛选

目的:诱导转座子Tn917随机插入炭疽杆菌染色体,产生在不同位点突变的突变体库,从中筛选芽孢形成缺陷型突变株。方法:用含转座子Tn917的质粒pLTV3转化炭疽杆菌,以低浓度红霉素诱导转座因发生转座,产生大量的突变株。进而用氯化三苯基四氮唑染色法和复红美蓝染色法从突变体库中筛选芽孢形成缺陷株;用Southern杂交法对芽孢形成缺陷株进行验证。结果:对2000个突变体进行了筛选,共得到6株芽孢形成缺陷株,在LB培养基中培养5d后,镜下仍未见有芽孢形成,呈现明显的芽孢形成缺陷特征。Southern杂交表明野生株无杂交带,突变株均有且只有1条杂交带,且杂交带的位置不尽相同。结论:转座子Tn917可以单拷贝随机诱变炭疽杆菌野生株,产生在不同位点突变的突变株。     

PNP降解相关基因温敏突变株的分离及其特性研究

通过接合转移将质粒pSC123上的转座子Tn5随机插入到DLL-E4基因组DNA中,从大约8,000个突变株中得到1株温度敏感型突变株MT54。根据转座子上的已知序列设计引物以MT54基因组DNA为模板进行PCR扩增,证实MT54的染色体中有转座子插入。MT54在30℃条件下能够以对硝基苯酚(p-nitrophenol,PNP)为唯一碳源生长,但在37℃不能生长。格里斯试色剂法检测NO_2~-的生成情况进一步证明了MT54的这种特性。通过30℃和37℃两种温度条件下MT54和原始出发菌株DLL-E4对PNP和对苯二酚降解情况的比较,推测温敏突变位点可能发生在与PNP降解相关的基因中。     

转座子Tn4560在吸水链霉菌应城变种中的转座

Tn4556是在弗氏链霉菌UC8592中发现的一个类似于Tn3的转座子,在它转坐的非必需区中间插入紫霉素抗性基因vph所组成的复合体(Tn4556::vph),称为Tn4560.把Tn4560克隆到一个温敏性质粒pMT660(由PIJ702衍生而来)构建的重组质粒(pMT660::Tn4560)称为pUC1169.pUC1169不能直接转化吸水链霉菌应城变种1O-22,但可以以一定的频率转化其衍生菌株Q105(至少丧失了一个内源质粒的受体菌株.)从转化子中检测DNA,可以观察到完整的PUC1169的存在(仍为高拷贝).将携带了pUC1169的Q105菌株的孢子悬液以一定的稀释度涂布到无抗生素的平板上获得单个分散的菌株,把平板放在39℃下培养,待菌落长出丰满的孢子后,再分别影印到含有紫霉素和硫链丝菌素的培养基平板上,分离紫霉素抗性(vio^r)和硫链丝菌素敏感(thio^s)的菌落,即为pMT660“自杀”,而Tn4560在细胞中发生了转座的个体.从18个这类菌落中提取总DNA,经PvuⅡ酶解后,在琼脂糖凝胶上电泳,把电泳后的DNA转移到硝酸纤维膜上,与非放射性方法标记的pUC1169探针杂交揭示,每一个衍生菌株都丢失了对应于载体PMT660的区域,却在染色体或内源质粒的不同位点上保留了Tn4560.从vio^r thio^s的突变体中已获得了5102-Ⅲ抗生素生物合成的阻断突变株.     

Tn2促进基因缺失与R质粒接合转移有关的遗传学证据

通过R100-1的接合转移和非接合转移的温度选择两种方法分别获得了一系列mer::Tn2突变体。回复试验和杂交结果表明,通过接合转移分得的22株mer::Tn2突变体中有7株发生了长度不等的缺失;但通过非接合转移的温度选择法获得的17株mer::Tn2突变体中没有发现缺失株。这一结果进一步证明Tn2促进缺失形成与R因子的接合转移有关。     

嗜水气单胞菌若干毒力因子同时缺失的突变株的构建及特性分析

以携带质粒pAM12 0 (Tcr Tn916 )的大肠杆菌CG12 0株为供体菌 ,采用滤膜接合法与受体菌嗜水气单胞菌J_1株 (cfzr)进行接合转移 ,在含Tc和cfz选择平板上进行筛选。共获接合转移菌落 380 0个 ,其接合频率为 3× 10 - 5(按供体细胞计算 )。任取 38个接合子 ,提取基因组DNA ,以嗜水气单胞菌特异性 16SrDNA引物进行PCR扩增 ,所有接合子均阳性。为证明Tn916确实插入基因组 ,以四环素基因 (tet)引物进行PCR扩增 ,结果所有抗性接合子均扩增出一条特异条带。与亲本J_1株相比 ,所有接合子的主要毒力因子如蛋白酶、溶血素、DNA酶和淀粉酶等均不表达 ,对小鼠失去致病力 ,其LD50 大于 10 9CFU。接合子连传 10次后 ,四环素抗性消失 ,但毒力未恢复 ,说明通过转座子Tn916的插入可获得稳定的无毒嗜水气单胞菌突变株。Tn916引起嗜水气单胞菌毒力性状改变的机制有待研究 ,推测可能与该菌染色体上存在Tn916的热点或毒力岛有关。     

Insertional specificity of transposon Tn5 in Acinetobacter sp.

Suicide plasmid pJB4JI, containing transposon Tn5 and phage Mu, was introduced from Escherichia coli 1830 into Acinetobacter sp. strain HO1-N and Acinetobacter calcoaceticus BD413. Kanamycin-resistant (Kmr) exconjugants of HO1-N and BD413, isolated on complex medium, were screened for auxotrophic requirements. Over 10,000 Kmr clones were examined, but no auxotrophs were detected. Several Kmr exconjugants of BD413 and HO1-N, obtained from independent matings, were chosen for further study. All Tn5-containing strains exhibited kanamycin phosphotransferase activity. Kmr strains lacked plasmid DNA as determined by three plasmid screening procedures, and the Kmr phenotype was not transferable by conjugal matings to kanamycin-sensitive BD413, HO1-N, or E. coli HB101. The chromosomal location of Tn5 insertions in independently isolated Kmr exconjugants of BD413 and HO1-N was characterized by restriction endonuclease mapping and hybridization studies. Results obtained from Southern hybridization studies were consistent with a single Tn5-specific insertion site in HO1-N and two such sites in BD413. Phage Mu sequences were not detected in Tn5-containing Acinetobacter sp.     

Transposon Tn5 mutagenesis in Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica

In matings between Escherichia coli 2492(pJB4JI) and Erwinia carotovora subsp. carotovora Ecc71 and E. carotovora subsp. atroseptica Eca12, Kmr Gms transconjugants were obtained at high frequencies, indicating instability of the Mu-containing plasmid pJB4JI and transposition of Tn5 into the recipient genome. This was verified by Southern blot hybridization with pRZ102 DNA containing Tn5 as the 32P-labeled probe. Examination of Kmr Gms transconjugants of Ecc71 and Eca12 disclosed that a proportion (2 to 3%) were either auxotrophic or defective in catabolism of specific carbohydrates. Spontaneous prototrophic revertants were obtained for all markers with the exception of ilv, tyr, and suc. Genetic and physical data indicate that scattered insertions of Tn5 from pJb4JI into the chromosome of Ecc71 and Eca12 produced a variety of altered phenotypes due mostly to single insertions of Tn5 not accompanied by Mu DNA.     

Tn4351 transposes in Bacteroides spp. and mediates the integration of plasmid R751 into the Bacteroides chromosome.

The gene for resistance to erythromycin and clindamycin, which is carried on the conjugative Bacteroides plasmid, pBF4, has been shown previously to be part of an element (Tn4351) that transposes in Escherichia coli. We have now introduced Tn4351 into Bacteroides uniformis 0061 on the following two suicide vectors: (i) the broad-host-range IncP plasmid R751 (R751::Tn4351) and (ii) pSS-2, a chimeric plasmid which contains 33 kilobases of pBF4 (including Tn4351) cloned into the IncQ plasmid RSF1010 and which is mobilized by R751. When E. coli HB101, carrying either R751::Tn4351 or R751 and pSS-2, was mated with B. uniformis under aerobic conditions, Emr transconjugants were detected at a frequency of 10(-6) to 10(-5) (R751::Tn4351) or 10(-8) to 10(-6) (R751 and pSS-2). In matings involving pSS-2, all Emr transconjugants contained simple insertions of Tn4351 in the chromosome, whereas in matings involving R751::Tn4351, about half of the Emr transconjugants had R751 cointegrated with Tn4351 in the chromosome. Of the Emr transconjugants, 13% were auxotrophs. Bacteroides spp. which had R751 cointegrated with Tn4351 in the chromosome did not transfer R751 or Tn4351 to E. coli HB101 or to isogenic B. uniformis, nor did the intergrated R751 mobilize pE5-2, an E. coli-Bacteroides shuttle vector that contains a transfer origin that is recognized by R751.     

Rhizobium phaseoli symbiotic mutants with transposon Tn5 insertions.

Rhizobium phaseoli CFN42 DNA was mutated by random insertion of Tn5 from suicide plasmid pJB4JI to obtain independently arising strains that were defective in symbiosis with Phaseolus vulgaris but grew normally outside the plant. When these mutants were incubated with the plant, one did not initiate visible nodule tissue (Nod-), seven led to slow nodule development (Ndv), and two led to superficially normal early nodule development but lacked symbiotic nitrogenase activity (Sna-). The Nod- mutant lacked the large transmissible indigenous plasmid pCFN42d that has homology to Klebsiella pneumoniae nitrogenase (nif) genes. The other mutants had normal plasmid content. In the two Sna- mutants and one Ndv mutant, Tn5 had inserted into plasmid pCFN42d outside the region of nif homology. The insertions of the other Ndv mutants were apparently in the chromosome. They were not in plasmids detected on agarose gels, and, in contrast to insertions on indigenous plasmids, they were transmitted in crosses to wild-type strain CFN42 at the same frequency as auxotrophic markers and with the same enhancement of transmission by conjugation plasmid R68.45. In these Ndv mutants the Tn5 insertions were the same as or very closely linked to mutations causing the Ndv phenotype. However, in two mutants with Tn5 insertions on plasmid pCFN42d, an additional mutation on the same plasmid, rather than Tn5, was responsible for the Sna- or Ndv phenotype. When plasmid pJB4JI was transferred to two other R. phaseoli strains, analysis of symbiotic mutants was complicated by Tn5-containing deleted forms of pJB4JI that were stably maintained.     

Transposon mutagenesis and strain construction in Zymomonas mobilis

Conjugative or mobilizable plasmids carrying the transposable elements Tn5, Tn501 or mini Mu were readily transferred from Escherichia coli donors into Zymomonas mobilis recipients with frequencies depending both on donor and recipient strain used. With the exception of pULB113 (RP4::mini Mu), all foreign plasmids exhibited high instability in Z. mobilis transconjugants under both selective and non-selective conditions. Transposition events and consequent mutagenesis occurred readily in Z. mobilis transconjugant strains, with Tn5 and Tn501 being far less successful than mini Mu. Transposon mutagenesis with the help of mini Mu resulted in the isolation of a large number of independent auxotrophs with polyauxotrophs, cysteine, methionine and isoleucine requiring-isolates being the most frequent. When chromosomal DNA from all these mutants was digested with various restriction enzymes and the resulting restriction patterns were hybridized with a mini Mu probe, the majority of these mutants appeared to have insertions at different sites of the chromosome. Thus, transposon mutagenesis by mini Mu is proven to be a simple and efficient tool for mutant production and the genetic analysis of Z. mobilis.     

Transposon insertion mutagenesis of Pseudomonas aeruginosa with a Tn5 derivative: application to physical mapping of the arc gene cluster

For insertional mutagenesis of Pseudomonas aeruginosa, a derivative of the kanamycin-resistance (KmR) transposon Tn5 was constructed (Tn5-751) that carried the trimethoprim-resistance (TpR) determinant from plasmid R751 as an additional marker. Double selection for KmR and TpR avoided the isolation of spontaneous aminoglycoside-resistant mutants which occur at high frequencies in P. aeruginosa. As a delivery system for the recombinant transposon, plasmid pME305, a derivative of the broad-host-range plasma RP1, proved effective; pME305 is temperature-sensitive at 43 degrees C for maintenance in Escherichia coli and P. aeruginosa and deleted for IS21 and the KmR and primase genes. In matings with an E. coli donor carrying pME9(= pME305::Tn5-751), transposon insertion mutants of P. aeruginosa PAO were recovered at approx. 5 X 10(-7)/donor at 43 degrees C. Among Tn5-751 insertional mutants 0.9% were auxotrophs. A thr::Tn5-751 mutation near the recA-like locus rec-102 is useful for the construction of recombination-deficient strains. Several arc::Tn5-751 mutants could be isolated that were defective in anaerobic utilization of arginine as an energy source. From three of these mutants the arc gene region was cloned into an E. coli vector plasmid. Since Tn5-751 has a single EcoRI site between the TpR and KmR genes, EcoRI-generated fragments carrying either resistance determinant plus adjacent chromosomal DNA could be selected separately in E. coli. Thus, a restriction map of the arc region was constructed and verified by hybridization experiments. The arc genes were tightly clustered, confirming earlier genetic evidence.     

Regulation of glutamine synthetase formation in Escherichia coli: characterization of mutants lacking the uridylyltransferase.

A lambda phage (lambdaNK55) carrying the translocatable element Tn10, conferring tetracycline resistance (Tetr), has been utilized to isolate glutamine auxotrophs of Escherichia coli K-12. Such strains lack uridylyltransferase as a result of an insertion of the TN10 element in the glnD gene. The glnD::Tn10 insertion has been mapped at min 4 on the E. coli chromosome and 98% contransducible by phage P1 with dapD. A lambda transducing phage carrying the glnD gene has been identified. A glnD::Tn10 strain synthesizes highly adenylylated glutamine synthetase under all conditions of growth and fails to accumulate high levels of glutamine synthetase in response to nitrogen limitation. However, this strain, under nitrogen-limiting conditions, allows synthesis of 10 to 20 milliunits of biosynthetically active glutamine synthetase per mg of protein, which is sufficient to allow slow growth in the absence of glutamine. The GlnD phenotype in E. coli can be suppressed by the presence of mutations which increase the quantity of biosynthetically active glutamine synthetase.     

Single-site chromosomal Tn5 insertions affect the export of pectolytic and cellulolytic enzymes in Erwinia chrysanthemi EC16

Exponentially growing cells of Erwinia chrysanthemi EC16 usually export about 98% of their pectate lyase (PL) and protease, about 40% of their polygalacturonase (PG), and about 60% of their cellulase (endoglucanase or carboxymethyl cellulase; CL). By using the R plasmid, pJB4JI (pPH1JI::Mu::Tn5), three independent Tn5 insertion mutants were obtained that exported normal levels of protease but 10% or less of PL, PG, and CL. Physical analysis revealed that single copies of Tn5 had inserted into the E. chrysanthemi chromosome, producing a similar export-defective (Out-) phenotype. The synthesis of PL, PG, and CL was not affected by the Tn5 insertions. These enzymes were released from the mutants on spheroplast formation, indicating that they were located in the periplasmic space. Tn5 insertions caused the loss of a 35-kilodalton periplasmic protein, but did not alter the outer membrane protein composition. The findings are discussed with respect to the current knowledge on protein export in gram-negative bacteria.     

Tn 7 inserts in both orientations at a single chromosomal location and apparently forms cointegrates in Pasteurella multocida

Pasteurella multocida transconjugants isolated after mating with Escherichia coli strains that carry one or the other of two Tn7-containing suicide plasmids, pRKTV5 and pUW964 (pRKTV5::Tn5), were analysed. These plasmids have the ColE1 replication origin and were thus expected to deliver transposons but not be maintained as free replicons in Pasteurella. Five out of six transconjugants selected for acquisition of Tn7 from E. coli (pRKTV5) had simple insertions of the transposon, in either orientation, at a single chromosomal location, while the sixth had pRKTV5 integrated at the same location. By contrast, all of 27 transconjugants selected for acquisition of either Tn7 or Tn5 from E. coli (pUW964) maintained pUW964. Of seven subsequently examined at the molecular level, all had pUW964 (in one case, a deletion derivative) integrated at the same location as the Tn7 insertions obtained with pRKTV5. A copy of Tn7 was present at each boundary between the integrated plasmids (pRKTV5 or pUW964) and the chromosome in each strain. The two copies of Tn7 at either end of an integrated plasmid were either in the same (six cases) or in opposite (two cases) orientations with respect to each other. These seem to be products of replicative transposition by Tn7 but can also derive from conservative mechanisms.     

Mutagenesis by insertion of drug resistance transposon Tn7 into a vibrio species

A halotolerant, collagenolytic strain of Vibrio sp. was conjugated with an Escherichia coli strain carrying plasmid RP4. The plasmid was transferred to and maintained in the Vibrio and could be subsequently transferred in matings to suitably marked stains of the same species. After conjugation with an E. coli carrying the cointegrate plasmid RP4::Mu cts61::Tn7, Vibrio transconjugants were selected that carried Tn7 inserted into the bacterial chromosome. A large proportion of these transconjugants were auxotrophic, showing that plasmid suicide by Mu can be used to isolate Tn7-derived mutants in Vibrio. Approximately half of the auxotrophs isolate Tn7-derived mutants in Vibrio. Approximately half of the auxotrophs isolated were ilv mutants, all of which exhibited the same phenotype. Thus, although Tn7 insertion can induce auxotrophy, including trp, thy, his and ura, in Vibrio, there does appear to be a hot spot for integration in the ilv operon.