Optimization of extracellular 5-aminolevulinic acid production from Escherichia coli transformed with ALA synthase gene of Bradyrhizobium japonicum

Extracellular accumulation of 5-aminolevulinic acid (ALA) by an E. coli overexpressing ALA synthase (ALAS) was achieved by inserting a hemA gene from Bradyrhizobium japonicum and expressed under the control of T7 promoter. At pH 7.0 extracellular ALA reached up to 15 mM in a jar fermenter with an addition of glycine (30 mM) and succinate (90 mM) in the medium. ALA accumulation was increased to 20 mM by adding levulinic acid (30 mM) to the cultures.     

Cloning, expression, and characterization of 5-aminolevulinic acid synthase from Rhodopseudomonas palustris KUGB306

The hemA gene encoding 5-aminolevulinic acid synthase (ALAS) was cloned from the genomic DNA of photosynthetic bacterium Rhodopseudomonas palustris KUGB306. The deduced protein (ALAS) of this gene contained 409 amino acids. The hemA gene was subcloned into an expression vector pGEX-KG and the encoded protein was overexpressed as a fusion protein with glutathione-S-transferase (GST) in Escherichia coli BL21. The recombinant ALAS was purified and isolated free of the fusion partner (GST) by affinity purification on glutathione-Sepharose 4B resin and cleavage of the purified fusion protein by thrombin protease. The optimum pH and temperature of the recombinant ALAS was found to be at pH 7.5-8.0 and 35-40 degrees C, respectively. The Km value of the enzyme was 2.01 mM for glycine and 49.55 microM for succinyl-CoA. The enzyme activity was strongly inhibited by Pb2+, Fe2+, Co2+, Cu2+, and Zn2+ at 1 mM, but slightly affected by Mg2+ and K+. The recombinant ALAS required pyridoxal 5'-phosphate (PLP) as a cofactor for catalysis. Removal of this cofactor led to complete loss of the activity. Ultraviolet-visible spectroscopy with the ALAS suggested the presence of an aldimine linkage between the enzyme and PLP.     

重组Rhodobacter sphaeroides hemA表达的调控

RhodobactersphaeroideshemA编码5氨基乙酰丙酸合酶(ALAS),催化磷酸吡哆醛依赖性琥珀酰CoA和甘氨酸缩合成ALA.将R.spaeroideshemA导入E.coli进行表达,当hemA具有与lac启动子相同的转录方向时,ALAS有活性.lac启动子与hemA之间的距离会影响ALAS在不同培养基上的表达.E.coli宿主菌对ALAS表达、ALA产量有显著影响,在实验所用6种菌株中,E.coliDH1是最佳宿主菌(P<0.05).ALAS表达还与碳源有关,琥珀酸为碳源时,重组ALAS活性最高(P<0.05),以乳酸为碳源时,ALAS活性很低.重组ALAS活性也受培养基pH值影响,pH6.5时,活性最高(P<0.05).     

5-aminolevulinic acid biosynthesis in Escherichia coli coexpressing NADP-dependent malic enzyme and 5-aminolevulinate synthase

5-aminolevulinate (ALA) synthase (E.C. 2.3.1.37), which mediates the pyridoxal phosphate-dependent condensation of glycine and succinyl-CoA, encoded by the Rhodobacter sphaeroides hemA gene, enables Escherichia coli strains to produce ALA at a low level. To study the effect of the enhanced C4 metabolism of E. coli on ALA biosynthesis, NADP-dependent malic enzyme (maeB, E.C. 1.1.1.40) was coexpressed with ALA synthase in E. coli. The concentration of ALA was two times greater in cells coexpressing maeB and hemA than in cells expressing hemA alone under anaerobic conditions with medium containing glucose and glycine. Enhanced ALA synthase activity via coupled expression of hemA and maeB may lead to metabolic engineering of E. coli capable of large-scale ALA production.     

Effect of culture conditions on production of 5-aminolevulinic acid by recombinant Escherichia coli

Aminolevulinic acid (ALA) is formed by the enzyme ALA synthase (hemA gene). Then ALA is converted to Porphobilinogen (PBG) by the ALA dehydratase (hemB gene). For the overproduction of ALA, we used an Escherichia coli BL21(DE3) containing a hemA gene from Bradyrhzobium japonicum, which was created in our previous work. The effects of pH on the ALA synthase and ALA dehydratase were investigated. The ALA synthase and ALA dehydratase activities were dependent on the pH of the medium, with maximal activities occurring at pH 6.5 and 8.0 respectively. At pH 6.5, extracellular ALA reached 23 mM in a jar-fermenter. In addition, the effects of some nutritional factors, such as nitrogen source and the ratio of carbon to nitrogen (C/N) on the fermentative production of ALA were investigated. The highest ALA production was found with 8:1 of C/N ratio. Among various nitrogen sources, the tryptone might be a useful one for ALA production.     

表达酿酒酵母ALAS的重组大肠杆菌胞外5-氨基乙酰丙酸的产量和纯化

5-氨基乙酰丙酸(5-aminolevulinate,ALA)由5-氨基乙酰丙酸合酶(5-aminolevulinate synthase,ALAS)催化产生。利用重组细菌在大肠杆菌合成ALA已有不少研究。重组真核生物ALAS在大肠杆菌合成ALA的研究没有报道。酿酒酵母ALAS在大肠杆菌重组表达,在摇瓶培养条件下,分析了胞外ALA的产量,重组菌的生长状况和细胞中ALAS的活性,利用两种国产树脂纯化ALA,毛细管电泳分析确定ALA纯度在LB培养基中,初始pH6.5,含有20mmol/L的酮戊酸、20mmol/L琥珀酸和20mmol/L的甘氨酸,37℃下诱导培养12h,胞外ALA的产量为162mg/L培养基。纯化的ALA纯度达到90%。     

Effect of culture pH on the extracellular production of 5-aminolevulinic acid by Rhodobacter sphaeroides from volatile fatty acids

Summary 5-Aminolevulinic acid(ALA) production by Rhodobacter sphaeroides was investigated at various pH with levulinic acid addition using a volatile fatty acids medium prepared from the mandarin orange peel supplemented with glycine. At neutral pH (6.8 and 7.0), extracellular ALA production was up to 16 mM, while low production of ALA(less than 3.5 mM) was observed at acidic pH (lower than 6.5) and less than 3.9 mM of ALA produced at alkaline pH (higher than 7.5). The higher ALA synthase activity observed at neutral pH might enhance the ALA production compared with that observed in acidic and alkaliphilic cultures.     

Enhancement of 5-aminolevulinate production with recombinant Escherichia coli using batch and fed-batch culture system

5-Aminolevulinate (ALA) production with recombinant Escherichia coli Rosetta (DE3)/pET28a(+)-hemA was studied. In batch fermentation, the addition of glucose and glycine was effective to improve ALA production. Then the fed-batch fermentation was conducted with continuous feeding of precursors. When the concentrations of succinic acid and glycine were 7.0 g/l and 4.0 g/l, respectively, in the feeding, the ALA yield reached 4.1g/l. But the molar yield (ALA/glycine) was decreased in the fed-batch fermentation compared to batch fermentation. And it was found that the pH control during fed-batch cultivation was very important for the cell growth and ALA production. A two-stage pH value controlling strategy was suggested, in which, the pH value in the first 6h was regulated at pH 5.9, after then at pH 6.2, and the ALA yield was as high as 6.6g/l via fed-batch fermentation.     

过量表达自身hemA基因的重组大肠杆菌发酵生产5-氨基乙酰丙酸的研究

研究了优化重组大肠杆菌产5-氨基乙酰丙酸（ALA）的条件,提高大肠杆菌发酵生产AL气的产量。在测定重组大肠杆菌GT48的生长曲线的基础上,确定诱导时间,优化摇瓶发酵条件。然后,进一步在5L发酵罐上进行间歇和流加发酵研究。摇瓶实验表明,细胞培养最佳初始pH为6．5,最佳诱导时间为稳定期前期,最佳接种量为2％,过高的葡萄糖浓度对细胞生长和产物合成均有一定的抑制作用。在5L发酵罐间歇发酵中,重组菌产ALA能力达到47．8mg／L。采用流加发酵可以进一步将产物产量提高到63．8mg／L。构建的过量表达自身的hemA基因的大肠杆菌具有较高的产ALA能力,通过发酵条件优化和采用流加发酵可以提高AL气产量。     

Construction of an expression vector for propionibacteria and its use in production of 5-aminolevulinic acid by Propionibacterium freudenreichii

Several promoters from Propionibacterium freudenreichii subsp. shermanii were isolated using a promoter probe vector, pCVE1, containing the Streptomyces cholesterol oxidase gene (choA) as a reporter gene. Three of four promoters isolated exhibiting a strong activity in Escherichia coli also expressed a strong activity in P. freudenreichii subsp. shermanii IFO12426. Using two promoters with a strong activity and a previously constructed shuttle vector, pPK705, shuttling between E. coli and Propionibacterium. we constructed expression vectors for propionibacteria. To overproduce 5-aminolevulinic acid (ALA), which is the first intermediate in the synthesis of porphyrins, the ALA synthase gene (hemA) from Rhodobacter sphaeroides was recombined with the expression vectors. The activity of ALA synthase in the recombinant P freudenreichii subsp. shermanii increased about 70-fold that in the strain without a vector. The recombinant Propionibacterium produced ALA at a maximum concentration of 8.6 mM in the absence of levulinic acid, an inhibitor of ALA dehydratase, with 1% glucose as a carbon source. The recombinant P. freudenreichii accumulated 18.8 mmol/g cells ALA in the presence of 1 mM levulinic acid and 30 mM glycine. The construction of an efficient expression vector will facilitate genetic studies of a vitamin B12 producer, Propionibacterium.     

High level production of 5-aminolevulinic acid by Propionibacterium acidipropionici grown in a low-cost medium

5-Aminolevulinic acid (ALA) is an intermediate in the biosynthesis of tetrapyrroles. Its current production is expensive. We have developed a low-cost medium for Propionibacterium acidipropionici to produce extracellular ALA. When grown at 35?°C on a medium containing 3?% (w/v) food-grade sodium lactate supplemented with 18?g glycine/l, 4.05?g succinate/l, 1.8?g glucose/l, pH 7, it produced ALA up to 7.7?g/l over 6?days. Plant-growth promoting activity assays showed that the ALA was biologically active.     

5-Aminolevulinic acid synthesis in Escherichia coli.

A hemA mutant of Escherichia coli containing a multicopy plasmid which complemented the mutation excreted 5-aminolevulinic acid (ALA) into the medium. [1-14C]glutamate was substantially incorporated into ALA by this strain, whereas [2-14C]glycine was not. Periodate degradation of labeled ALA showed that C-5 of ALA was derived from C-1 of glutamate. The synthesis of ALA by two sonicate fractions which had been processed by gel filtration and dialysis, respectively, was dependent on glutamate, ATP, NADPH, tRNA(Glu), and pyridoxal phosphate. tRNA(Glu) stimulated ALA synthesis in a concentration-dependent manner. Pretreatment with RNase reduced this stimulation. The amino acid sequence of the cloned insert, derived from the nucleotide sequence (J.-M. Li, C. S. Russell, and S. D. Cosloy, J. Cell Biol. 107:617a, 1988), showed no homology with any ALA synthase sequenced to date. These results suggest that E. coli synthesizes ALA by the C5 pathway from the intact five-carbon chain of glutamate.     

Cloning and structure of the hem A gene of Escherichia coli K-12

An Escherichia coli gene, which complements two independent hemA mutants of E. coli, has been cloned onto a multi-copy plasmid and both its strands have been sequenced. Both complemented mutants produce 5-aminolevulinic acid (ALA) and display fluorescence after 24h. The cloned sequence appears to encode a 46-kDa protein, which when produced in the maxicell procedure is processed to a 41-kDa protein as determined by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. The amino acid sequence of the cloned gene product shows no significant homologies with any cloned ALA synthase, nor with any protein, in two E. coli databanks. A second cloned gene fragment, which has its coding region 34 bp away from the coding region of the gene that complements hemA, has been identified as part of protein release factor 1(RF1), thus confirming the location of hemA at min 26.7 and mapping it precisely near RF1. We have shown that E. coli utilizes the intact five-carbon chain of glutamate for the synthesis of ALA [Li et al., J Bacteriol. 171 (1989b) 2547-2552].     

表达浑球红细菌hemA基因生产5-氨基乙酰丙酸的研究

5-氨基乙酰丙酸（5-aminolevulinate acid,ALA）在农业,工业,医药业具有广泛的应用。ALA由5-氨基乙酰丙酸合酶（5-aminolevulinate acid synthase, ALAS）催化产生,其生物合成受终产物血红素的反馈抑制。本研究克隆一种浑球红细菌的hemA基因,序列分析其与已报道的基因具有96％的同源性,蛋白质编码区域也发生改变,并利用生物信息学软件进行同源关系的分析。采用大肠杆菌重组技术,构建表达载体pET28a—hemA,表达了有活性的浑球红细菌（Rhodobacter sphaeroides）的ALAS,研究了IPTG诱导和PH对研究ALAS的影响,同时分析了重组菌株合成ALA的能力,测定胞外产量。结果表明,在PH6．5,30mmol／L琥珀酸和60mmol／L甘氨酸培养条件下,胞外ALA的最大合成量达到669mg／L。     

Cloning and characterization of genes involved in the biosynthesis of delta-aminolevulinic acid in Escherichia coli.

Several mutants of Escherichia coli that had lost their ability to synthesize delta-aminolevulinic acid (ALA) via the C5 pathway were isolated. Their defective loci were classified into two groups, AlaA- and AlaB-. The genes that complemented these mutations were cloned. Nucleotide sequencing indicated that the gene that complemented AlaA- was identical to hemL which is located at 4 min on the E. coli chromosome and encodes glutamate 1-semialdehyde aminotransferase. The gene complementing AlaB- contained an open reading frame (ORF) encoding a polypeptide of 207 amino acids that was found to be a new gene involved in the synthesis of ALA via the C5 pathway. Thus, we designated the gene hemM. The hemM gene was adjacent to hemA that is located at 27 min and previously thought to encode glutamyl-tRNA dehydrogenase. However, we found that hemA complemented both the AlaA- (hemL) and AlaB- (hemM) mutants defective in the C5 pathway although the transformants showed small colonies on the selective medium without ALA. These results suggest that hemA is not involved in the C5 pathway, but controls a second, minor pathway for the synthesis of ALA.     

琥珀酸脱氢酶或琥珀酰辅酶A合成酶缺失促进大肠杆菌积累5-氨基乙酰丙酸

5-氨基乙酰丙酸 (ALA) 是生物体内四吡咯类化合物的合成前体,在农业及医药领域应用广泛,是极具开发价值的高附加值生物基化学品。目前利用外源C4途径的重组大肠杆菌发酵生产ALA的研究主要利用LB培养基并添加葡萄糖和琥珀酸、甘氨酸等合成前体,成本较高。琥珀酸在C4途径中以琥珀酰辅酶A的形式直接参与ALA的合成。文中在以葡萄糖为主要碳源的无机盐培养基中研究了琥珀酰辅酶A下游代谢途径琥珀酸脱氢酶编码基因sdhAB和琥珀酰辅酶A合成酶编码基因sucCD缺失对ALA积累的影响。与仅表达异源ALA合成酶的对照菌株相比,sdhAB和sucCD缺失菌株ALA的产量分别提高了25.59%和12.40%,且ALA的积累不依赖于琥珀酸的添加和LB培养基的使用,从而大幅降低了生产成本,显示出良好的工业应用前景。     

重组α-环糊精葡萄糖基转移酶表达条件的优化及其产物专一性的分析

将来源于Bacillus sp 602 -1的α-环糊精葡萄糖基转移酶(ot-CGT)基因(cgt)插入到表达载体PQE30中,构建重组质粒PQE30/cgt,成功转化宿主菌E coli M15后,得到重组菌株E coli M15 (PQE30/cgt).在IPTG的诱导下得到酶表达的最适条件:TB培养基,0.01 mmol/L IPTG,诱导温度16℃,胞内酶比活力最高可达5 209 U/mL;加入IPTG 24 h后,添加甘氨酸和甘露醇会促使酶向胞外分泌.酶蛋白自诱导表达的适宜条件为在TB培养基中添加乳糖3.0 g/L,葡萄糖1.2 g/L,16℃培养96 h,酶比活力达到8 635 U/mL,明显高于IPTG诱导的效果.通过SDSPAGE验证了上述结论.酶催化转化实验表明:重组酶转化质量分数为1％可溶淀粉24h后,α-环糊精(α-CD)转化率可达38.2％,α和β的峰面积比约为3.4:1,α-CD具有较高的专一性,因此该重组α-CGT酶具有较好的工业化应用前景.     

Optimization of a heterologous signal peptide by site-directed mutagenesis for improved secretion of recombinant proteins in Escherichia coli

A heterologous signal peptide (SP) from Bacillus sp. G1 was optimized for secretion of recombinant cyclodextrin glucanotransferase (CGTase) to the periplasmic and, eventually, extracellular space of Escherichia coli. Eight mutant SPs were constructed using site-directed mutagenesis to improve the secretion of recombinant CGTase. M5 is a mutated SP in which replacement of an isoleucine residue in the h-region to glycine created a helix-breaking or G-turn motif with decreased hydrophobicity. The mutant SP resulted in 110 and 94% increases in periplasmic and extracellular recombinant CGTase, respectively, compared to the wild-type SP at a similar level of cell lysis. The formation of intracellular inclusion bodies was also reduced, as determined by sodium dodecyl sulfate-polyacrylamyde gel electrophoresis, when this mutated SP was used. The addition of as low as 0.08% glycine at the beginning of cell growth improved cell viability of the E. coli host. Secretory production of other proteins, such as mannosidase, also showed similar improvement, as demonstrated by CGTase production, suggesting that the combination of an optimized SP and a suitable chemical additive leads to significant improvements of extracellular recombinant protein production and cell viability. These findings will be valuable for the extracellular production of recombinant proteins in E. coli.     

Utilization of volatile fatty acids from the anaerobic digestion liquor of sewage sludge for 5-aminolevulinic acid production by photosynthetic bacteria

Using volatile fatty acids (VFA) from the anaerobic digestion liquor of sewage sludge, up to 9.2 mm 5-aminolevulinic acid (ALA) could be produced by Rhodobacter sphaeroides under anaerobic-light (5 kLux) conditions with repeated addition of levulinic acid (LA) and glycine and using a large inoculum (approx. 2 g/l of cells, initially from glutamate/malate medium). As the VFA medium also contained organic nitrogen sources such as glutamic acid, the cells were later grown up to about 2 g/l in the VFA medium instead of the glutamate/malate medium. ALA production was then again promoted by adding LA and glycine. Using this improved method, up to 9.3 mm ALA was produced by feeding propionate and acetate together with LA and glycine, indicating that VFA medium formed from sewage sludge could be useful for ALA production.