阿维莲霉菌中aveD基因缺失对阿维菌素合成的影响

利用aveD基因的缺失载体pCZ8(pKC1139::△aveD)对阿维菌素（Avermectin）的产生菌阿维链霉菌（Streptomyces avermitilis)76-9的aveD基因进行缺失获得aveD缺失突变株。经摇瓶发酵和HPLC检测,发现该突变株只产生阿链菌素B组分。说明将阿维链霉菌的aveD基因缺失,并不影响下游aveF的表达。缺失突变株的阿维菌素的总产量与出发菌株的总产量基本相同,突变株中B1的产量略有提高,阿维菌素B2的含量显著提高。     

阿维链霉菌中aveD基因缺失对阿维菌素合成的影响

利用aveD基因的缺失载体pCZ8(pKC1139∷△aveD)对阿维菌素(Avermectin)产生菌阿维链霉菌(Streptomyces avermitilis)76\|9的aveD基因进行缺失获得aveD缺失突变株。经摇瓶发酵和HPLC检测,发现该突变株只产生阿维菌素B组分。说明将阿维链霉菌的aveD基因缺失,并不影响下游aveF的表达。缺失突变株的阿维菌素的总产量与出发菌株的总产量基本相同,突变株中B1的产量略有提高,阿维菌素B2的含量显著提高。     

阿维菌素衍生物CHC-B1的突变生物合成

利用成功构建的基因缺失载体pLJ04(pKC1139∷△bkdF +△bkdH)对阿维菌素(avermectin)高产菌阿维链霉菌(Streptomyces avermitilis)76-02-e的bkdFGH基因进行缺失,获得的bkdFGH缺失突变株经过摇瓶发酵和HPLC检测,发现该突变株完全丧失了产生阿维菌素的能力。2-甲基丁酸及异丁酸的前体添加试验表明,当有外源前体存在时,突变株又能恢复阿维菌素合成的能力。将该bkdFGH基因缺失突变株命名为S.avermitilis bkd76-3。环己羧酸(CHC)前体添加试验及HPLC检测发现存在4种产物,经LC/MS分析验证,其中两种产物分别为CHC-B1和CHC-A2。     

杀粉蝶菌素A1生物合成基因簇中甲基转移酶PieB2的功能

【目的】研究杀粉蝶菌素A1产生菌中甲基转移酶基因pieB2的功能。【方法】利用接合转移和同源重组双交换的方法,构建pieB2基因缺失突变株,以及利用接合转移的方法,构建回补菌株。通过高保真PCR克隆pieB2基因到表达载体pET28a上,构建质粒pJTU5997,转化入大肠杆菌E.coliBL21(DE3)/pLysE中诱导表达。利用高效液相色谱检测PieB2的体外酶活。【结果】获得了pieB2基因缺失的双交换突变株。发酵结果显示,该突变株不再产生杀粉蝶菌素A1,而是积累了一种脱甲基产物。N-末端融合组氨酸标签的PieB2在大肠杆菌中获得可溶性表达,通过体外催化证明了PieB2甲基转移酶的功能。【结论】体内遗传实验和体外生化实验证明了PieB2作为甲基转移酶在杀粉蝶菌素A1合成中的作用。     

黄脂菌素生物合成基因簇中调控基因xanR3的功能

【目的】研究黄脂菌素产生菌灰黄链霉菌中编码ArsR家族转录调控蛋白(Arsenical resistance regulator)的xanR3基因的功能。【方法】利用大肠杆菌和链霉菌双亲本接合转移的方法,构建xanR3基因缺失突变株及回补突变株。利用cDNA在相邻同方向的基因间隔区进行PCR确定黄脂菌素生物合成基因簇中的转录单元。利用荧光定量RT-PCR方法进行突变株中黄脂菌素生物合成基因簇转录水平的检测。【结果】对得到的xanR3基因缺失突变株及回补突变株进行发酵,发现xanR3基因缺失突变株产黄脂菌素能力下降,回补菌株中黄脂菌素产量相比缺失突变株有一定程度的恢复,但仍未达到野生型水平。经鉴定,黄脂菌素生物合成基因簇中共有18个共转录单元,其中4个共转录单元在?xanR3突变株中转录水平明显下降。【结论】ArsR家族转录调控基因xanR3是黄脂菌素生物合成的正调控基因。     

杀念菌素/FR-008生物合成途径中转运基因fscTⅠ与fscTⅡ的功能

[目的]分析杀念菌素/FR-008生物合成途径中转运基因fscTⅠ和ficTⅡ的功能.[方法]构建转运基因fscTⅠ和fscTⅡ的敲除质粒pJTU4137,并通过接合转移和同源重组双交换的方法得到转运基因缺失突变株.转运基因fscTⅠ和ficTⅡ也被克隆到高拷贝质粒pJTU 1278上用于在链霉菌FR-008(Streptomyces sp.FR-008)的衍生菌株ZYJ-6中进行转运蛋白的过量表达.[结果]获得了转运蛋白缺失的双交换突变株LX10,发酵结果显示该突变株不再产生杀念菌素及其衍生物 ;过量表达转运蛋白的基因工程菌株LX11,其杀念菌素的产量约是对照菌株的1.5倍.[结论]体内遗传实验进一步证实FR-008生物合成途径中的fscTⅠ和fscTⅡ是ATP依赖的ABC转运基因,fscTⅠ与fscTⅡ的过量表达增加了杀念菌素的产量,为利用此方法提高其它多烯类抗生素的产量提供了例证.     

须糖多孢菌Saccharopolyspora pogona的核糖体工程改造对丁烯基多杀菌素合成的影响

核糖体工程是以微生物的各类抗生素抗性突变为筛选标记,高效获得次生代谢产物合成能力提高的突变株的一种育种新方法。通过核糖体工程技术,使用链霉素对须糖多孢菌Saccharopolyspora pogona进行抗性选育,以获得高产丁烯基多杀菌素突变菌株。对原始菌株和所获得的突变菌株代谢产物的研究发现,相对于原始菌株,其中突变株S13的丁烯基多杀菌素产量提高幅度最大,相比原始菌株提高了1.79倍。经质谱测定表明,其代谢物中比原始菌株多了一种丁烯基多杀菌素组分Spinosynα1。对抗性突变株S13的DNA序列进行分析,发现在编码核糖体S12蛋白的rps L基因保守区域中出现点突变,第314位和第320位的胞嘧啶(C)分别突变为腺嘌呤(A)和胸腺嘧啶(T),对应的氨基酸残基分别由脯氨酸突变为谷氨酰胺,丙氨酸突变为缬氨酸。研究显示,突变株S13遗传稳定性良好。     

酿酒酵母adh2和ald6双基因缺失突变株的构建

酿酒酵母乙醇合成代谢过程中, 阻断或削弱乙醛至乙酸代谢流不但能增强乙醇合成流, 同时还能降低发酵乙酸含量。本研究以乙醇脱氢酶Ⅱ(adh2)基因缺陷型酿酒酵母YS2-Dadh2为出发菌株, 应用长侧翼同源两步PCR(LFH-PCR)策略构建乙醛脱氢酶Ⅵ(ald6)基因敲除组件, 转化酿酒酵母YS2-Dadh2敲除ald6基因, 之后转入表达质粒pSH65到阳性克隆中, 半乳糖诱导表达Cre重组酶切除Kanr基因筛选标记, 最后, 传代丢失质粒pSH65获得单倍体ald6基因缺失突变株。利用同样的敲除组件和技术再次敲除其等位基因, 最终获得双基因缺失突变株YS2-△adh2-Dald6。发酵实验表明与出发菌株YS2相比, 突变株乙酸合成量降低18%, 乙醇最高产量提高12.5%。     

基于基因组挖掘的农抗120活性成分制霉菌素和丰加霉素的发现和鉴定

【目的】分析刺孢吸水链霉菌北京变种(农抗120产生菌)基因组和次级代谢产物组分,研究并鉴定农抗120产生菌中未被发现的活性组分。【方法】利用antiSMASH在线分析农抗120产生菌Streptomyces hygrospinosusvar.beijingensis基因组信息,锁定可能的制霉菌素和丰加霉素生物合成基因簇。利用HPLC和LC-MS等分析方法对农抗120产生菌发酵产物进行分析,同时利用制霉菌素和丰加霉素标准品作为对照,以鉴定该菌株代谢组分中的次级代谢产物。此外,通过构建目标基因簇大片段缺失突变株,并对所得突变株发酵产物进行检测,以确定生物合成基因簇与目的代谢产物的对应关系。【结果】本研究综合利用基因组序列分析、基因缺失突变株构建以及代谢产物检测方法,鉴定了农抗120产生菌中制霉菌素和丰加霉素两种活性成分,并确定了负责这些化合物合成的基因簇。【结论】本研究所构建的多重基因簇失活突变株为挖掘刺孢吸水链霉菌北京变种更多的天然次级代谢产物奠定了基础。     

2,3-丁二醇代谢途径关键酶基因敲除对克雷伯氏菌发酵产1,3-丙二醇的影响

2,3-丁二醇是克雷伯氏菌发酵产1,3-丙二醇的主要副产物,为减少2,3-丁二醇的产生,利用Red重组技术对克雷伯氏菌2,3-丁二醇合成途径关键酶基因budC和budA进行了敲除。突变株发酵性能实验结果表明,所获得的两株突变株生长性能受到不同程度的影响;budC基因的缺失使菌株1,3-丙二醇产量提高了10%,2,3-丁二醇降低为原来的70%,而budA基因缺失则使菌株无2,3-丁二醇和1,3-丙二醇的产生,但乳酸、琥珀酸、乙醇和乙酸的产量较出发菌株都有明显增长。通过进一步对budC基因缺失菌株主要产物分析,推测在该菌中存在2,3-丁二醇回补途径,这一结果为低副产物克雷伯氏菌的改造提供了新依据。     

Semi-synthetic DNA shuffling of aveC leads to improved industrial scale production of doramectin by Streptomyces avermitilis

The avermectin analog doramectin (CHC-B1), sold commercially as Dectomax, is biosynthesized by Streptomyces avermitilis. aveC, a gene encoding an unknown mechanistic function, plays an essential role in the production of doramectin (avermectin CHC-B1), modulating the production ratio of CHC-B1 to other avermectins, most notably the undesirable analog CHC-B2. To improve the production ratio for doramectin, the aveC gene was subjected to iterative rounds of semi-synthetic DNA shuffling. Libraries of shuffled aveC gene variants were transformed into S. avermitilis, screened using a miniaturized 96-well growth and production format, and analyzed by high throughput mass spectrometry to determine CHC-B2:CHC-B1 ratios. Several improved aveC variants were identified; the best shuffled gene encoded 10 amino acid mutations, and conferred a final CHC-B2:CHC-B1 ratio of 0.07:1, a 23-fold improvement over the starting gene (aveC wild type). Chromosomal insertion of an improved aveC shuffled gene into a high titer S. avermitilis strain yielded an improved doramectin production strain. This strain is under development to be used commercially, and is expected to provide considerable cost savings in large-scale manufacture, as well as significantly reducing by-product levels of CHC-B2 requiring disposal.     

Engineering the aveC gene to enhance the ratio of doramectin to its CHC-B2 analogue produced in Streptomyces avermitilis

Avermectin and its analogues are produced by the actinomycete Streptomyces avermitilis and are major commercial products for parasite control in the fields of animal health, agriculture, and human infections. Historically, the avermectin analogue doramectin (CHC-B1), which is sold commercially as Dectomax is co-produced during fermentation with the undesired analogue CHC-B2 at a CHC-B2:CHC-B1 ratio of 1.6:1. Although the identification of the avermectin gene cluster has allowed for characterization of most of the biosynthetic pathway, the mechanism for determining the avermectin B2:B1 ratio remains unclear. The aveC gene, which has an essential role in avermectin biosynthesis, was inactivated by insertional inactivation and mutated by site-specific mutagenesis and error-prone PCR. Several unrelated mutations were identified that resulted in improved ratios of the desirable avermectin analogue CHC-B1, produced relative to the undesired CHC-B2 fermentation component. High-throughput (HTP) screening of cultures grown on solid-phase fermentation plates and analysis using electrospray mass spectrometry was implemented to significantly increase screening capability. An aveC gene with mutations that result in a 4-fold improvement in the ratio of doramectin to CHC-B2 was identified. Subsequent integration of the enhanced aveC gene into the chromosome of the S. avermitilis production strain demonstrates the successful engineering of a specific biosynthetic pathway gene to significantly improve fermentation productivity of a commercially important product.     

Identification of a cyclohexylcarbonyl CoA biosynthetic gene cluster and application in the production of doramectin

The side chain of the antifungal antibiotic ansatrienin A from Streptomyces collinus contains a cyclohexanecarboxylic acid (CHC)-derived moiety. This moiety is also observed in trace amounts of omega-cyclohexyl fatty acids (typically less than 1% of total fatty acids) produced by S. collinus. Coenzyme A-activated CHC (CHC-CoA) is derived from shikimic acid through a reductive pathway involving a minimum of nine catalytic steps. Five putative CHC-CoA biosynthetic genes in the ansatrienin biosynthetic gene cluster of S. collinus have been identified. Plasmid-based heterologous expression of these five genes in Streptomyces avermitilis or Streptomyces lividans allows for production of significant amounts of omega-cyclohexyl fatty acids (as high as 49% of total fatty acids). In the absence of the plasmid these organisms are dependent on exogenously supplied CHC for omega-cyclohexyl fatty acid production. Doramectin is a commercial antiparasitic avermectin analog produced by fermenting a bkd mutant of S. avermitilis in the presence of CHC. Introduction of the S. collinus CHC-CoA biosynthetic gene cassette into this organism resulted in an engineered strain able to produce doramectin without CHC supplementation. The CHC-CoA biosynthetic gene cluster represents an important genetic tool for precursor-directed biosynthesis of doramectin and has potential for directed biosynthesis in other important polyketide-producing organisms.     

阿维链霉菌中aveD基因阻断对阿维菌素合成的影响

利用用于基因破坏的重组质粒pCZ2 (pKC1 1 39∷ 475bpaveD)对阿维菌素 (Avermectin)产生菌阿维链霉菌 (Streptomycesavermitilis) 76- 9的aveD基因进行插入失活 ,将获得的aveD破坏子进行摇瓶发酵和阿维菌素初步提取和HPLC检测 ,发现破坏子仅产生四个主要组分 ,但它们的保留时间分别比Bla、Blb、B2a和B2b的略长。进而将粗提液纯化并获得晶体 ,以UV、IR、NMR ( 1H NMR和13C NMR)和MS进行结构分析 ,并结合HPLC检验 ,证明它们属于C5 氧 阿维菌素B。说明阿维链霉菌的aveD基因破坏 ,不仅丧失了合成阿维菌素A组分的能力 ,也造成了其下游的aveF基因不能表达 ,因此只产生了C5 氧 阿维菌素B。     

Fatty-acid biosynthesis in a branched-chain alpha-keto acid dehydrogenase mutant of Streptomyces avermitilis

Fatty-acid biosynthesis by a branched-chain alpha-keto acid dehydrogenase (bkd) mutant of Streptomyces avermitilis was analyzed. This mutant is unable to produce the appropriate precursors of branched-chain fatty acid (BCFA) biosynthesis, but unlike the comparable Bacillus subtilis mutant, was shown not to have an obligate growth requirement for these precursors. The bkd mutant produced only straight-chain fatty acids (SCFAs) with membrane fluidity provided entirely by unsaturated fatty acids (UFAs), the levels of which increased dramatically compared to the wild-type strain. The levels of UFAs increased in both the wild-type and bkd mutant strains as the growth temperature was lowered from 37 degrees C to 24 degrees C, suggesting that a regulatory mechanism exists to alter the proportion of UFAs in response either to a loss of BCFA biosynthesis, or a decreased growth temperature. No evidence of a regulatory mechanism for BCFAs was observed, as the types of these fatty acids, which contribute significantly to membrane fluidity, did not alter when the wild-type S. avermitilis was grown at different temperatures. The principal UFA produced by S. avermitilis was shown to be delta 9-hexadecenoate, the same fatty acid produced by Escherichia coli. This observation, and the inability of S. avermitilis to convert exogenous labeled palmitate to the corresponding UFA, was shown to be consistent with an anaerobic pathway for UFA biosynthesis. Incorporation studies with the S. avermitilis bkd mutant demonstrated that the fatty acid synthase has a remarkably broad substrate specificity and is able to process a wide range of exogenous branched chain carboxylic acids into unusual BCFAs.     

A second branched-chain alpha-keto acid dehydrogenase gene cluster (bkdFGH) from Streptomyces avermitilis: its relationship to avermectin biosynthesis and the construction of a bkdF mutant suitable for the production of novel antiparasitic avermectins.

A second cluster of genes encoding the E1 alpha, E1 beta, and E2 subunits of branched-chain alpha-keto acid dehydrogenase (BCDH), bkdFGH, has been cloned and characterized from Streptomyces avermitilis, the soil microorganism which produces anthelmintic avermectins. Open reading frame 1 (ORF1) (bkdF, encoding E1 alpha), would encode a polypeptide of 44,394 Da (406 amino acids). The putative start codon of the incompletely sequenced ORF2 (bkdG, encoding E1 beta) is located 83 bp downstream from the end of ORF1. The deduced amino acid sequence of bkdF resembled the corresponding E1 alpha subunit of several prokaryotic and eukaryotic BCDH complexes. An S. avermitilis bkd mutant constructed by deletion of a genomic region comprising the 5' end of bkdF is also described. The mutant exhibited a typical Bkd- phenotype: it lacked E1 BCDH activity and had lost the ability to grow on solid minimal medium containing isoleucine, leucine, and valine as sole carbon sources. Since BCDH provides an alpha-branched-chain fatty acid starter unit, either S(+)-alpha-methylbutyryl coenzyme A or isobutyryl coenzyme A, which is essential to initiate the synthesis of the avermectin polyketide backbone in S. avermitilis, the disrupted mutant cannot make the natural avermectins in a medium lacking both S(+)-alpha-methylbutyrate and isobutyrate. Supplementation with either one of these compounds restores production of the corresponding natural avermectins, while supplementation of the medium with alternative fatty acids results in the formation of novel avermectins. These results verify that the BCDH-catalyzed reaction of branched-chain amino acid catabolism constitutes a crucial step to provide fatty acid precursors for antibiotic biosynthesis in S. avermitilis.     

发酵液中多拉菌素的提取和萃取条件研究

采用单因素实验,分别研究提取试剂、发酵液放置时间、pH值和温度对发酵液中多拉菌素提取效果的影响;然后以乙酸乙酯为萃取试剂,研究萃取次数及萃取体积对多拉菌素萃取效果的影响。结果显示,甲醇为最佳提取试剂;发酵液在pH为3～11、温度为20～80℃的条件下放置144 h,多拉菌素均能稳定存在,提取得到的多拉菌素的质量浓度没有显著变化;浓缩提取液液经2倍体积乙酸乙酯萃取2次即可。该条件下多拉菌素的质量浓度和萃取率分别为151.78μg/mL和98.00%。     

阿维链霉菌的诱变育种

以阿维链霉菌(Streptomyces avermitilis)76-12为出发菌株,采用亚硝基胍、吖啶橙、紫外线和氯化锂分别对其孢子和原生质体进行诱变,经抗代谢物理性筛选,获得一系列高产突变株,其中N-1-2高产突变株的发酵单位是出发菌株的2.47倍。实验中同时获得了只产阿维菌素a组分的突变株G-32、Bla组分含量高的Ave8菌株和产蓝绿色孢子的突变株UA-G等。     

Catabolism of Branched-Chain α-Keto Acids in Enterococcus faecalis: the bkd Gene Cluster, Enzymes, and Metabolic Route

Genes encoding a branched-chain alpha-keto acid dehydrogenase from Enterococcus faecalis 10C1, E1alpha (bkdA), E1beta (bkdB), E2 (bkdC), and E3 (bkdD), were found to reside in the gene cluster ptb-buk-bkdDABC. The predicted products of ptb and buk exhibited significant homology to the phosphotransbutyrylase and butyrate kinase, respectively, from Clostridium acetobutylicum. Activity and redox properties of the purified recombinant enzyme encoded by bkdD indicate that E. faecalis has a lipoamide dehydrogenase that is distinct from the lipoamide dehydrogenase associated with the pyruvate dehydrogenase complex. Specific activity of the ptb gene product expressed in Escherichia coli was highest with the substrates valeryl-coenzyme A (CoA), isovaleryl-CoA, and isobutyryl-CoA. In cultures, a stoichiometric conversion of alpha-ketoisocaproate to isovalerate was observed, with a concomitant increase in biomass. We propose that alpha-ketoisocaproate is converted via the BKDH complex to isovaleryl-CoA and subsequently converted into isovalerate via the combined actions of the ptb and buk gene products with the concomitant phosphorylation of ADP. In contrast, an E. faecalis bkd mutant constructed by disruption of the bkdA gene did not benefit from having alpha-ketoisocaproate in the growth medium, and conversion to isovalerate was less than 2% of the wild-type conversion. It is concluded that the bkd gene cluster encodes the enzymes that constitute a catabolic pathway for branched-chain alpha-keto acids that was previously unidentified in E. faecalis.