共查询到18条相似文献，搜索用时 46 毫秒
1.
拥有Ⅰ型聚羟基脂肪酸酯（PHA）合酶基因的嗜水气单胞菌CGMCC 0911株可利用月桂酸而不能利用葡萄糖作为碳源积累PHBHHx。将氯霉素抗性基因（Cm）插入到该基因中,获得带有I型PHA合酶断裂基因（phaC::Cm）的自杀质粒pFH10。自杀质粒pFH10通过接合作用转入嗜水气单胞菌CGMCC 0911株中并发生体内同源重组,Cm被整合到基因组上,获得Ⅰ型PHA合酶缺失突变株。DNA序列测定证明了这一结果。GC分析表明,突变株不再产生PHBHHx,但却可利用月桂酸或葡萄糖积累中长链PHA,明显表明野生型嗜水气单胞菌基因组中存在另一个编码Ⅱ型PHA合酶的基因,且只有Ⅰ型PHA合酶被钝化后,这个功能被隐藏的Ⅱ型PHA合酶才可在细胞中发挥作用。 相似文献
2.
拥有Ⅰ型聚羟基脂肪酸酯(PHA)舍酶基因的嗜水气单胞菌CGMCC 0911株可利用月桂酸而不能利用葡萄糖作为碳源积累PHBHHx。将氯霉素抗性基因(cm)插入到该基因中,获得带有Ⅰ型PHA合酶断裂基因(phaC：：Cm)的自杀质粒pFH10。自杀质粒DFH10通过接合作用转入嗜水气单胞菌CGMCC 0911株中并发生体内同源重组,Cm被整合到基因组上,获得Ⅰ型PHA合酶缺失突变株。DNA序列测定证明了这一结果。GC分析表明,突变株不再产生PHBHHx,但却可利用月桂酸或葡萄糖积累中长链PHA,明显表明野生型嗜水气单胞菌基因组中存在另一个编码Ⅱ型PHA合酶的基因,且只有Ⅰ型PHA合酶被钝化后,这个功能被隐藏的Ⅱ型PHA合酶才可在细胞中发挥作用。 相似文献
3.
分别利用葡萄糖或葡萄糖酸钠与十一碳酸、月桂酸与十一碳酸为混合碳源进行嗜水气单孢菌 (Aeromonashydrophila)菌株 4AK4的摇瓶培养 ,实现了含有 3 羟基戊酸 (3HV)单体的聚羟基脂肪酸酯的微生物合成。当使用葡萄糖或葡萄糖酸钠与十一碳酸为混合碳源时 ,野生型A .hydrophila 4AK4及含有 3 羟基丁酸辅酶A合成基因phaA和phaB的重组A .hydrophila 4AK4 (pTG01)能够合成-3-羟基丁酸(3HB)与-3HV的共聚物 ,且葡萄糖或葡萄糖酸钠与十一碳酸比例为 1∶1时最利于细胞生长和PHA的积累。当使用月桂酸和十一碳酸为混合碳源时 ,A .hydrophila4AK4能够合成-3HB、3HV与 β-羟基己酸 (3HHx)的共聚物 ,且随着混合碳源中十一碳酸的含量增加 ,A .hydrophila4AK4合成的PHA中-3HV的比例增加 ,而-3HB和-3HHx的比例降低. 相似文献
4.
5.
6.
聚羟基脂肪酸酯(Polyhydroxyalkanoate,PHA)是一系列生物合成的高分子材料,其单体可由多种3-羟基脂肪酸(3-hydroxyalkanoate,3HA)构成^[1]。PHA物理和机械性能的变化很大,从高脆性到弹性体,这跟它们的单体成分有很大关系^[2]。短链和中长链单体共聚的PHA比短链单体或中长链单体聚合得到的PHA有着更好的性能^[3]。在1994年,豚鼠气单胞菌(Aeromonas caviae)FA440被发现能以偶数碳原子数脂肪酸或植物油作为碳源在体内积累PHBHHx^[4]其PHA生物合成基因被成功克隆^[5]。根据亚基数目和底物特异性,PHA合成的关键酶,即PHA合酶或PhaC,被分成了3种类型。A．caviae的PHA合酶属于第1类PHA合酶^[6]。PHA合酶的一些类型含有一些保守的基因序列,该特征可被用于克隆,特别是第Ⅱ类PHA合酶^[2,8]。嗜水气单胞菌(Aeromonas hydrophila)WQ和A．hydrophila 4AK4是能够合成PHBHHx的另外两种菌株,其中A．hydrophila 4AK4已被用作大规模生产PHBHHx。就目前来说,不管生长条件怎么改变,其合成的PHBHHx中3羟基己酸单体(3-hydroxyhexanoate,3HHx)的含量始终在12％～17％之间变化^[9]。而A．hydrophila WQ合成的PHBHHx中则含有6％～14％ 3HHx。本论文研究了A．hydrophila WQ的PHA生物合成及其分子基础。 相似文献
7.
8.
9.
为了提高PHAMCL在门多萨假单胞菌NK-01中的积累,采用单因素实验和正交实验确立了发酵生产PHAMCL的最佳条件,即以PHA产量为指标的最佳发酵条件为15 g/L葡萄糖浓度、C/N=50、发酵时间48 h,该条件下获得产量0.8 g/L以上的PHA;以PHA占菌体干重百分含量为指标的最佳发酵条件为10 g/L葡萄糖浓度、C/N=60、发酵时间48 h,该条件下获得占菌体干重50%以上的PHA。该研究将为门多萨假单胞菌NK-01用于PHAMCL的规模化生产提供理论依据。 相似文献
10.
聚羟基脂肪酸酯解聚酶(polyhydroxyalkanoate depolymerase,PHAD)可用于聚羟基脂肪酸酯(polyhydroxyalkanoate,PHA)的降解回收,为开发热稳定性好的PHAD,本研究在大肠杆菌(Escherichiacoli)BL21(DE3)中成功表达了来自短须嗜热单孢菌(Thermomonospora umbrina)的PHA解聚酶(TumPHAD),并通过二硫键理性设计获得了热稳定性提升的突变体A190C/V240C,其最适温度为60℃,比野生型提高20℃,50℃半衰期为7h,是野生型酶的21倍。将突变体A190C/V240C用于典型PHA之一的聚羟基丁酸酯(polyhydroxybutyrate,PHB)降解,在50℃条件下,PHB的2 h和12 h降解率较野生型分别提高了2.1倍和3.8倍。本研究获得的TumPHAD突变体A190C/V240C具有耐高温、热稳定性好和PHB降解能力强的特点,对PHB的降解回收具有重要意义。 相似文献
11.
Polyhydroxyalkanoate (PHA) synthase genes (phaC) were cloned from two Aeromonas hydrophila strains named WQ and 4AK5, respectively. Both strains are able to produce PHBHHx copolyesters consisting of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). Sequence analysis showed that there was only 2 bp difference between these two PHA synthase genes, corresponding to two-amino acid difference at positions of 437 and 458 of the two synthases. PHA productivity and its monomer content produced by A. hydrophila WQ and A. hydrophila 4AK5 were quite different. A. hydrophila WQ accumulated 33% PHBHHx of its cell dry weight (CDW) with 5 mol% 3HHx in the copolyester when cultured in lauric acid for 48 h. Yet A. hydrophila 4AK5 was able to produce 43% PHBHHx of the CDW with 14 mol% 3HHx under the same condition. Hetero-expression of PHA synthase genes of A. hydrophila WQ and A. hydrophila 4AK5, respectively, in Escherichia coli XL1-Blue led to PHBHHx accumulation of 24% and 39% of the CDW and the 3HHx content in PHBHHx were 6 and 15 mol%, respectively. This indicated that the function of these two PHA synthases were different due to these two different residues at positions of 437 and 458. Site specific mutation was carried out to change these two amino acid residues. Results showed that the changes on either of the two amino acids negatively affected the PHA productivity. 相似文献
12.
非核糖体肽是微生物体内一类具有天然生物活性的次生代谢物,由非核糖体肽合成酶催化生成。而AHA2474和AHA2476是嗜水气单胞菌ATCC7966中两个编码非核糖体肽合成酶的基因。利用同源重组技术分别构建了AHA2474、AHA2476基因缺失株,并对其生理特性进行测定。结果表明,与野生株相比,缺失株的溶血性和胞外蛋白酶活性均显著增强,而产铁能力明显减弱;在缺铁条件下,缺失株的生长能力较弱,补充铁离子后又能恢复生长。同时在过氧化氢应激下ΔAHA2474菌株具有更大的耐受性。以上研究结果提示AHA2474和AHA2476基因可能通过影响铁离子动态平衡过程来调控该菌的生理特性,同时也表明非核糖体肽在该菌致病性方面起作用,为探究该菌的致病机制及防治策略提供理论依据。 相似文献
13.
David A. Randolph James W. Verbsky Liping Yang Yifu Fang Razqallah Hakem Larry E. Fields 《Transgenic research》1996,5(6):413-420
Gene targeting by double homologous recombination in murine embryonic stem (ES) cells is a powerful tool used to study the cellular consequences of specific genetic mutations. A typical targeting construct consists of a neomycin phosphotransferase (neo) gene flanked by genomic DNA fragments that are homologous to sequences in the target chromosomal locus. Homologous DNA fragments are typically cloned from a murine genomic DNA library. Here we describe an alternative approach whereby the inducible nitric oxide synthase (NOS2) gene locus is partially mapped and homologous DNA sequences obtained using a long-range PCR method. A 7 kb NOS2 amplicon is used to construct a targeting vector where theneo gene is flanked by PCR-derived homologous DNA sequences. The vector also includes a thymidine kinase (tk) negative-selectable marker gene. Following transfection into ES cells, the PCR-based targeting vector undergoes efficient homologous recombination into the NOS2 locus. Thus, PCR-based gene targeting can be a valuable alternative to the conventional cloning approach. It expedites the acquisition of homologous genomic DNA sequences and simplifies the construction of targeting plasmids by making use of defined cloning sites. This approach should result in substantial time and cost savings for appropriate homologous recombination projects. 相似文献
14.
Song D Coughlin J Ju J Zhou X Shen B Zhao C Deng Z 《Acta biochimica et biophysica Sinica》2008,40(4):319-326
Sequence analysis of oxazolomycin (OZM) biosynthetic gene cluster from Streptomyces albus JA3453 revealed a gene, ozmH , encoding a hybrid polyketide and non-ribosomal pep-tide enzyme. Tandem ketosynthase (KS) domains (KS10–1 and KS10–2 ) were characterized and they show significant homol-ogy with known KSs. Using an alternative method that involves RecA-mediated homologous recombination, the negative selection marker sacB gene, and temperature-sensitive replications, site-directed mutagenesis of the catalytic triad amino acid cysteines were carried out in each of the tandem KS domains totest the function they play in OZM biosynthesis. HPLC-mass spectrometry analysis of the resulting mutant strains showed that KS10–2 is essential for OZM biosynthesis but KS10–1 is not indispensable and might serve as a "redundant" domain. These results confirmed the existence of an "extra domain" in complex polyketide synthase. 相似文献
15.
Endo M Osakabe K Ono K Handa H Shimizu T Toki S 《The Plant journal : for cell and molecular biology》2007,52(1):157-166
We have previously reported the production of a rice cell line tolerant to the acetolactate synthase (ALS)-inhibiting herbicide bispyribac (BS), and demonstrated that the BS-tolerant phenotype was due to a double mutation in the rice ALS gene. We further indicated that while changing either of the two amino acids (W548 L or S627I) individually resulted in a BS-tolerant phenotype, conversion of both amino acids simultaneously conferred increased tolerance to BS. As the BS-tolerant cell line had lost the ability to regenerate during two years of tissue culture selection, we attempted to introduce these two point mutations into the rice ALS gene via gene targeting (GT). Using our highly efficient Agrobacterium-mediated transformation system in rice, we were able to regenerate 66 independent GT rice plants from 1500 calli. Furthermore, two-thirds of these plants harbored the two point mutations exclusively, without any insertion of foreign DNA such as border sequences of T-DNA. The GT plants obtained in the present study are therefore equivalent to non-GM herbicide-tolerant rice plants generated by conventional breeding approaches that depend on spontaneous mutations. Surprisingly, GT rice homozygous for the modified ALS locus showed hyper-tolerance to BS when compared to BS-tolerant plants produced by a conventional transgenic system; ALS enzymatic activity in plants homozygous for the mutated ALS gene was inhibited only by extremely high concentrations of BS. These results indicate that our GT method has successfully created novel herbicide-tolerant rice plants that are superior to those produced by conventional mutation breeding protocols or transgenic technology. 相似文献
16.
Rehm BH 《Biotechnology letters》2006,28(4):207-213
PHAs (polyhydroxyalkanoates = biopolyester) composed of hydroxy fatty acids represent a rather complex class of storage polymers
synthesized by various bacteria and archaea and are deposited as water-insoluble cytoplasmic nano-sized inclusions. These
spherical particles are composed of a polyester core surrounded by phospholipids and proteins. The key enzymes of polyester
biosynthesis and polyester particle formation are the polyester synthases, which catalyze the formation of polyesters. Various
metabolic routes have been identified and established in bacteria to provide substrate for polyester synthases. Although not
essential for particle formation, non-covalently attached proteins, the so-called phasins, can be found at the particle surface
and are considered as structural proteins. Protein engineering of polyester synthases and phasins was used to shed light into
the topology of these granule attached proteins. Biopolyesters and the respective micro-/nano-structures are currently considered
as biocompatible and biodegradable biomaterials with numerous potential applications particularly in the medical field.
Received 12 October 2005; Revisions requested 1 November 2005; Revisions received 25 November 2005; Accepted 25 November 2005 相似文献
17.
Advanced bacterial polyhydroxyalkanoates: Towards a versatile and sustainable platform for unnatural tailor-made polyesters 总被引：1，自引：0，他引：1
Polyhydroxyalkanoates (PHAs) are biopolyesters that generally consist of 3-, 4-, 5-, and 6-hydroxycarboxylic acids, which are accumulated as carbon and energy storage materials in many bacteria in limited growth conditions with excess carbon sources. Due to the diverse substrate specificities of PHA synthases, the key enzymes for PHA biosynthesis, PHAs with different material properties have been synthesized by incorporating different monomer components with differing compositions. Also, engineering PHA synthases using in vitro-directed evolution and site-directed mutagenesis facilitates the synthesis of PHA copolymers with novel material properties by broadening the spectrum of monomers available for PHA biosynthesis. Based on the understanding of metabolism of PHA biosynthesis, recombinant bacteria have been engineered to produce different types of PHAs by expressing heterologous PHA biosynthesis genes, and by creating and enhancing the metabolic pathways to efficiently generate precursors for PHA monomers. Recently, the PHA biosynthesis system has been expanded to produce unnatural biopolyesters containing 2-hydroxyacid monomers such as glycolate, lactate, and 2-hydroxybutyrate by employing natural and engineered PHA synthases. Using this system, polylactic acid (PLA), one of the major commercially-available bioplastics, can be synthesized from renewable resources by direct fermentation of recombinant bacteria. In this review, we discuss recent advances in the development of the PHA biosynthesis system as a platform for tailor-made polyesters with novel material properties. 相似文献
18.
An approximately 4.9 kb Sau3A I genomic DNA fragment from the Streptomyces aureofaciens NRRL 2209 aiding in the biosynthesis of PHB in recombinant Escherichia coli has been sequenced and analysed for phaC gene. The putative phaC(Sa) gene of 2 kb is 79.1% GC rich and encodes a 63.5 kDa protein. It expressed under its own promoter and significant PHA synthase activity was detected in the recombinant E. coli. This is the first putative PHA synthase gene reported from a Streptomyces sp. with serine as the active nucleophile in the conserved lipase box. The phaC(Sa) was found in close proximity to a regulatory gene, which apparently regulated the phaC expression. 相似文献