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1.
Vitreoscilla hemoglobin (VHb) has been successfully used to enhance production of foreign proteins in several microorganisms including
Escherichia coli. We compared the expression of an oxygen-dependent foreign protein, green fluorescent protein (GFP) under co-expression of
VHb in two typical industrial E. coli strains, BL21 (a B derivative) and W3110 (a K12 derivative), which have different metabolic properties. We employed the nar oxygen-dependent promoter for self-tuning regulation of VHb expression due to the natural transition of dissolved oxygen
(DO) level during culture. We observed several interesting and differing behaviors in cultures of the two strains. VHb co-expression
showed a positive influence on expression, and even on solubility, of GFP in both strains; while strain BL21 had the higher
GFP expression level, W3110 showed higher solubility of expressed GFP. GFP expression in strain BL21 was very largely affected
by variation of aeration environments, but W3110 was not significantly impacted. We surmised that this arose from different
oxygen utilization abilities and indeed the two strains showed different patterns of oxygen uptake rate. Interestingly, the
VHb co-expressing W3110 strain exhibited a peculiar increasing pattern of GFP expression during the late culture period even
under low aeration conditions and this enhancement was more obvious in large-scale cultures. Therefore, this strain could
be successfully employed in practical large-scale production cultures where DO levels tend to be limited.
Electronic Publication 相似文献
2.
Co-expression of Vitreoscilla hemoglobin (VHb) can enhance production of foreign proteins in several microorganisms, including Escherichia coli. Production of foreign proteins [green fluorescent protein (GFP) and organophosphorous hydrolase (OPH)] has been examined in two typical industrial E. coli strains, W3110 (a K12 derivative) and BL21 (a B derivative). In particular, we investigated the effects of VHb co-expression and media glucose concentration on target protein production. We employed the nar O(2)-dependent promoter for self-tuning of VHb expression based on the natural changes in dissolved O(2) levels over the duration of culture. Foreign protein production in strain BL21 was decreased by a high glucose concentration but co-expression of VHb had no effect on this. In contrast, co-expression of VHb in strain W3110 overrode the glucose-induced repression and resulted in steady expression of foreign proteins. 相似文献
3.
Production of green fluorescent protein (GFP) as a model foreign protein using different culture scales under co-expression
ofVitreoscilla hemoglobin (VHb) in the industrialEscherichia coli strain W3110 (a K12 derivative), was examined. It was found that the VHb co-expressing W3110, exhibited an exceptional and
sustained production ability during cell cultures using different scales, while the VHb non-expressing strain showed variable
production levels. This high and sustained production ability indicates that the VHb co-expressingE. coli W3110, could be successfully employed for practical large-scale production cultures without the need for serious consideration
of scale-up problems. 相似文献
4.
《Mutation Research Letters》1983,119(2):135-144
46 chemicals of various classes and structures, including 30 known animal carcinogens, were evaluated for genotoxic effects using the Escherichia coli rec assay with strains WP2 (wild-type) and WP100 (uvrA−1recA−) in qualitative and quantitative spot tests and in quantitative suspension tests. The rec assay detected 17 of 30 known carcinogens as genotoxic agents, including mitomycin C and diethylnitrosamine, both negative in the Salmonella/Ames test as utilized in these studies. The rec assay in conjunction with the Salmonella/Ames test 30 known carcinogens as genotoxic agents. Azo/aminoazo carcinogens showed little genotoxicity, and the aromatic amine 2-acetylaminofluorene was non-genotoxic in the rec assay. The rec assay was more effective than pol tests with E. coli strains W3110/p3478 and strains WP2/WP67. Effectiveness of the rec assay was related to the DNA repair-defective nature of the uvrA− recA− genotype of strain WP100. 相似文献
5.
Sebnem O. Erenler Salih Gencer Hikmet Geckil Benjamin C. Stark Dale A. Webster 《Applied Biochemistry and Microbiology》2004,40(3):241-248
The hemoglobins found in unicellular organisms show a great deal of chemical reactivity, protecting cells against oxidative stress, and hence have been implicated in a wider variety of potential functions than those traditionally associated with animal and plant hemoglobins. There are well-documented studies showing that bacteria expressing Vitreoscilla hemoglobin (VHb), the first prokaryotic hemoglobin characterized, have better growth and oxygen uptake rates than their VHb counterparts. Here, the expression of VHb, its effect on the growth and antioxidant enzyme status of cells under different culture conditions was studied by cloning the complete regulatory and coding sequences (vgb) for VHb in Enterobacter aerogenes. Contrary to what has been reported for Escherichia coli, the expression of vgb in E.aerogenes decreased several fold under 10% of atmospheric oxygen (2% oxygen) and its growth was not greatly improved by the presence of VHb. Measured either as viable cells or total cell mass, untransformed E. aerogenes grew better than the recombinant strains. At the late exponential phase, however, the vgb-bearing strain was determined to have a higher cell number and total cell mass than the strain bearing only the plasmid vector with no vgb insert. The VHb expressing strain also had an oxygen uptake rate several fold higher than its counterparts. Given that oxidative stress may occur upon elevated oxygen exposure and be balanced by the action of antioxi-dative compounds, the level of antioxidative response of E. aerogenes expressing VHb was also studied. The VHb expressing strain had substantially (1.5–2.6-fold) higher catalase activity than strains not expressing VHb. Both VHb+ and VHb- strains, however, showed similar levels of superoxide dismutase activity. The activity of both enzymes was also growth phase dependent. Stationary phase cells of all strains showed 2–5-fold higher activity for these enzymes than cells at the exponential phase. 相似文献
6.
Tony Sanny Marina Arnaldos Stephanie A. Kunkel Krishna R. Pagilla Benjamin C. Stark 《Applied microbiology and biotechnology》2010,88(5):1103-1112
Escherichia coli strain FBR5, which has been engineered to direct fermentation of sugars to ethanol, was further engineered, using three different
constructs, to contain and express the Vitreoscilla hemoglobin gene (vgb). The three resulting strains expressed Vitreoscilla hemoglobin (VHb) at various levels, and the production of ethanol was inversely proportional to the VHb level. High levels
of VHb were correlated with an inhibition of ethanol production; however, the strain (TS3) with the lowest VHb expression
(approximately the normal induced level in Vitreoscilla) produced, under microaerobic conditions in shake flasks, more ethanol than the parental strain (FBR5) with glucose, xylose,
or corn stover hydrolysate as the predominant carbon source. Ethanol production was dependent on growth conditions, but increases
were as high as 30%, 119%, and 59% for glucose, xylose, and corn stover hydrolysate, respectively. Only in the case of glucose,
however, was the theoretical yield of ethanol by TS3 greater than that achieved by others with FBR5 grown under more closely
controlled conditions. TS3 had no advantage over FBR5 regarding ethanol production from arabinose. In 2 L fermentors, TS3
produced about 10% and 15% more ethanol than FBR5 for growth on glucose and xylose, respectively. The results suggest that
engineering of microorganisms with vgb/VHb could be of significant use in enhancing biological production of ethanol. 相似文献
7.
Shaohua Wang Fei Liu Zhongwen Hou Gongli Zong Xiqiang Zhu Peixue Ling 《World journal of microbiology & biotechnology》2014,30(4):1369-1376
Oxygen deficiency is a critical factor during the fermentation production of natamycin. In order to alleviate oxygen limitation and enhance the yield of natamycin, the vgb gene, encoding Vitreoscilla hemoglobin (VHb) was inserted into pSET152 with its native promoter and integrated into the chromosome of Streptomyces gilvosporeus (S. gilvosporeus). The expression of VHb was determined by Western blotting. The activity of expressed VHb was confirmed by the observation of VHb-specific CO-difference spectrum with a maximal absorption at 419 nm for the recombinant. Integration of the empty plasmid pSET152 did not affect natamycin production of S. gilvosporeus. While the vgb-harboring strain exhibited high natamycin productivity, reaching 3.31 g/L in shake flasks and 8.24 g/L in 1-L fermenters. Compared to the wild strain, expression of VHb, increased the natamycin yield of the strain bearing vgb by 131.3 % (jar fermenter scale) and 175 % (shake flask scale), respectively, under certain oxygen-limiting condition. Addition of an extra copy of the vgb gene in S. gilvosporeus-vgb2 did not enhance the natamycin production obviously. These results provided a superior natamycin-producing strain which can be directly used in industry and a useful strategy for increasing yields of other metabolites in industrial strains. 相似文献
8.
Asli Giray Kurt Emel Aytan Ufuk Ozer Burhan Ates Hikmet Geckil Professor 《Biotechnology journal》2009,4(7):1077-1088
Given the well-established beneficial effects of Vitreoscilla hemoglobin (VHb) on heterologous organisms, the potential of this protein for the production of L -DOPA and dopamine in two bacteria, Citrobacter freundii and Erwinia herbicola, was investigated. The constructed recombinants bearing the VHb gene (vgb+) had substantially higher levels of cytoplasmic L -DOPA (112 mg/L for C. freundii and 97 mg/L for E. herbicola) than their respective hosts (30.4 and 33.8 mg/L) and the vgb– control strains (35.6 and 35.8 mg/L). Further, the vgb+ recombinants of C. freundii and E. herbicola had 20-fold and about two orders of magnitude higher dopamine levels than their hosts, repectively. The activity of tyrosine phenol-lyase, the enzyme converting L -tyrosine to L -DOPA, was well-correlated to cytoplasmic L -DOPA levels. As cultures aged, higher tyrosine phenol-lyase activity of the vgb+ strains was more apparent. 相似文献
9.
T. Sar Y. Chen Y. Bai B. Liu P. Agarwal B.C. Stark M.Y. Akbas 《Letters in applied microbiology》2021,72(4):484-494
Enhancement of the desulfurization activities of Paenibacillus strains 32O-W and 32O-Y were investigated using dibenzothiophene (DBT) and DBT sulfone (DBTS) as sources of sulphur in growth experiments. Strains 32O-W, 32O-Y and their co-culture (32O-W plus 32O-Y), and Vitreoscilla hemoglobin (VHb) expressing recombinant strain 32O-Yvgb and its co-culture with strain 32O-W were grown at varying concentrations (0·1–2 mmol l−1) of DBT or DBTS for 96 h, and desulfurization measured by production of 2-hydroxybiphenyl (2-HBP) and disappearance of DBT or DBTS. Of the four cultures grown with DBT as sulphur source, the best growth occurred for the 32O-Yvgb plus 32O-W co-culture at 0·1 and 0·5 mmol l−1 DBT. Although the presence of vgb provided no consistent advantage regarding growth on DBTS, strain 32O-W, as predicted by previous work, was shown to contain a partial 4S desulfurization pathway allowing it to metabolize this 4S pathway intermediate. 相似文献
10.
Y.‐T. Horng K.‐C. Chang C.‐C. Chien Y.‐H. Wei Y.‐M. Sun P.‐C. Soo 《Letters in applied microbiology》2010,50(2):158-167
Aim: To develop an approach to enhance polyhydroxybutyrate (PHB) production via the coexpressed phaCAB and vgb genes controlled by arabinose PBAD promoter in Escherichia coli. Method and Results: The polyhydroxyalkanoates (PHAs) synthesis operon, (phaCAB), from Ralstonia eutropha was overexpressed under the regulation of the arabinose PBAD promoter in Escherichia coli, and the vgb gene encoding bacterial haemoglobin from Vitreoscilla stercoraria (VHb) was further cloned at downstream of phaCAB to form an artificial operon. The cell dry weight (CDW), PHB content and PHB concentration were enhanced around 1·23‐, 1·57‐, and 1·93‐fold in the engineered cell harbouring phaCAB–vgb (SY‐2) upon 1% arabinose induction compared with noninduction (0% arabinose). Furthermore, by using a recombinant strain harbouring PBAD promoter‐vgb along with native promoter‐phaCAB construction, the effect of vgb expression level on PHB biosynthesis was positive correlation. Conclusions: The results exploit the possibility to improve the PHB production by fusing the genes phaCAB–vgb from different species under the arabinose regulation system in E. coli. It also demonstrates that increase in VHb level enhances the PHB production. Significance and Impact of the Study: We were successful in providing a new coexpressed system for PHB synthesis in E. coli. This coexpressed system could be regulated by arabinose inducer, and is more stable and cheaper than other induced systems (e.g. IPTG). Furthermore, it could be applied in many biotechnology or fermentation processes. 相似文献
11.
Aerobic expression of Vitreoscilla hemoglobin improves the growth performance of CHO‐K1 cells
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Mariana Juárez Claudia H. González‐De la Rosa Elisa Memún Juan‐Carlos Sigala Alvaro R. Lara 《Biotechnology journal》2017,12(3)
Inefficient carbon metabolism is a relevant issue during the culture of mammalian cells for the production of biopharmaceuticals. Therefore, cell engineering strategies to improve the metabolic and growth performance of cell lines are needed. The expression of Vitreoscilla stercoraria hemoglobin (VHb) has been shown to significantly reduce overflow metabolism and improve the aerobic growth of bacteria. However, the effects of VHb on mammalian cells have been rarely studied. Here, the impact of VHb on growth and lactate accumulation during CHO‐K1 cell culture was investigated. For this purpose, CHO‐K1 cells were transfected with plasmids carrying the vgb or gfp gene to express VHb or green fluorescence protein (GFP), respectively. VHb expression increased the specific growth rate and biomass yields on glucose and glutamine by 60 %, and reduced the amount of lactate produced per cell by 40 %, compared to the GFP‐expression controls. Immunofluorescence microscopy showed that VHb is distributed in the cytoplasm and organelles, which support the hypothesis that VHb could serve as an oxygen carrier, enhancing aerobic respiration. These results are useful for the development of better producing cell lines for industrial applications. 相似文献
12.
Enhanced production of acetoin and butanediol in recombinant Enterobacter aerogenes carrying Vitreoscilla hemoglobin gene 总被引:2,自引:0,他引:2
Geckil H Barak Z Chipman DM Erenler SO Webster DA Stark BC 《Bioprocess and biosystems engineering》2004,26(5):325-330
Microbial production of butanediol and acetoin has received increasing interest because of their diverse potential practical uses. Although both products are fermentative in nature, their optimal production requires a low level of oxygen. In this study, the use of a recombinant oxygen uptake system on production of these metabolites was investigated. Enterobacter aerogenes was transformed with a pUC8-based plasmid carrying the gene (vgb) encoding Vitreoscilla (bacterial) hemoglobin (VHb). The presence of vgb and production of VHb by this strain resulted in an increase in viability from 72 to 96 h in culture, but no overall increase in cell mass. Accumulation of the fermentation products acetoin and butanediol were enhanced (up to 83%) by the presence of vgb/VHb. This vgb/VHb related effect appears to be due to an increase of flux through the acetoin/butanediol pathway, but not at the expense of acid production. 相似文献
13.
Dissolved oxygen (DO)-controlled nar promoter expression vectors were constructed, and their expression efficiency was compared with that of the T7 promoter pET22 expression vector by expressing human growth hormone (hGH), enhanced green fluorescence protein (EGFP), and β-tyrosinase in Escherichia coli cells. The nar promoter expression vector pRBS, which was engineered with a 5′-untranslated region and ribosomal binding site for the T7 promoter, expressed hGH at a rate of up to 32% of the total cellular proteins (TCP) in E. coli W3110narL−. The expression level of hGH was further enhanced, up to ∼42% of the TCP, by adding the N-terminal peptide tag of β-galactosidase to hGH, which was comparable to the expression of ∼43% of the TCP in pET-lac:hGH/BL21(DE3). A further engineered expression vector, pRBS(fnr), which coexpressed fumarate/nitrate reductase (fnr), expressed more EGFP than pET22 in BL21(DE3). In addition, recombinant β-tyrosinase was successfully expressed at a rate of up to ∼45% of the TCP in pRBS(fnr) in W3110narL−. From these results, the DO-controlled nar promoter system developed in this study can be considered a reliable and cost-effective expression system for protein production, especially in large-scale fermentation, as an alternative to the pET/BL(DE3) system. 相似文献
14.
High cell-density cultivations are the preferred system for biomolecules production by Escherichia coli. It has been previously demonstrated that a strain of E. coli with a modified substrate transport system is able to attain high cell densities in batch mode, due to the very low overflow metabolism displayed. The use of elevated amounts of glucose from the beginning of the cultivation, eliminates the existence of substrate gradients due to deficient mixing at large-scale. However, the large amounts of oxygen demanded resulted in microaerobic conditions after some hours of cultivation, even at small-scale. In this work, the effect of expressing the Vitreoscilla hemoglobin (VHb) in the engineered strain during batch cultures using high-glucose concentrations was tested. Together, the expression of VHb and the modified substrate transport system resulted in a 33% increase of biomass production compared to the parental strain (W3110) lacking the VHb in batch cultivations using 25 g/L of glucose. When 50 g/L of glucose were used, expression of VHb in the modified strain led to 11% higher biomass production compared to W3110. The VHb also increased the growth rates of the strains by about 30% in the aerobic phase and more than 200% in the microaerobic phase of batch cultivation. 相似文献
15.
Gregg Bogosian Patricia J. L. Morris Deborah B. Weber James F. Kane 《Journal of industrial microbiology & biotechnology》1993,11(4):235-241
Summary This study examined the transfer of the plasmid pBGH1, an expression vector for bovine somatotropin (BST), fromEscherichia coli K-12 strain W3110G [pBGH1] to indigenous microorganisms present in flasks containing Missouri River water. Strain LBB269 is a nalidixic acid-resistant derivative of W3110G which was used as a plasmid-free control strain in these studies. Water samples were inoculated with strains W3110G [pBGH1] and LBB269; after 21 days of incubation the number of viable colony-forming units (CFU) of W3110G [pBGH1] and LBB269 were reduced from an initial level of about 1×107 CFU per ml to less than 1 CFU per 100 ml. At this time indigenous microbes resistant to both ampicillin and tetracycline (the antibiotic resistance markers on pBGH1) were isolated from 100 ml of water from each of the flasks inoculated with either strain W3110G [pBGH1] or LBB269. Plasmid DNA was isolated from these organisms and examined for sequences containing the gene for BST from pBGH1, using a polymerase chain reaction (PCR) assay. As expected, the day 0 sample from the flask inoculated withE. coli K-12 strain W3110G [pBGH1] gave a positive PCR response and the day 0 sample from the flask inoculated withE. coli K-12 strain LBB269 gave a negative PCR response. All of the day 21 samples containing indigenous microbes isolated from flasks that were inoculated with either W3110G [pBGH1] or LBB269 were negative in the PCR assay, indicating that the target sequence from pBGH1 was not present in any of these indigenous microorganisms. The results of this particular assay indicate that pBGH1 or the portion of pBGH1 including the BST structural gene had not been transferred from W3110G [pBGH1] to indigenous microbial inhabitants of the Missouri River water flasks during this study. 相似文献
16.
《Journal of Fermentation and Bioengineering》1993,75(2):155-157
Three Escherichia coli strains, two recA− strains (DH1 and YK537) and one recA+ strain (KS476) harboring human proapo A-I expression plasmid pUS(pAI), were cultivated in fed-batch mode using a synthetic medium and the amounts of human proapo A-I accumulation were compared under various cultivation conditions. In the expression plasmid, nine proapo A-I genes were tandemly ligated downstream of the tac promoter. Experimental results indicated that selection of the host strain and cultivation temperature was important. Among the three E. coli strains checked, strain DH1 yielded the most effective production of human proapo A-I at 30°C. 相似文献
17.
Microbial production of L -glutamate and L -glutamine by recombinant Corynebacterium glutamicum harboring Vitreoscilla hemoglobin gene vgb 总被引:1,自引:0,他引:1
Liu Q Zhang J Wei XX Ouyang SP Wu Q Chen GQ 《Applied microbiology and biotechnology》2008,77(6):1297-1304
Vitreoscilla hemoglobin (VHb) gene vgb equipped with a native promoter Pvgb or a tac promoter Ptac was introduced into Corynebacterium glutamicum ATCC14067, respectively. Ptac was proven to be more suitable for expressing VHb protein in higher concentration in both Escherichia coli and C. glutamicum strains compared with the native vgb promoter Pvgb. VHb-expressing C. glutamicum exhibited higher oxygen uptake rate and enhanced cell growth. Recombinant C. glutamicum harboring vgb gene equipped with Ptac promoter produced 23% more l-glutamate in shake-flask culture and grew to 30% more cell density and formed 22% more l-glutamate in fermentor studies compared with the wild-type strain. When a site-directed mutagenesis in which Tyr405 was replaced
by a phenylalanine residue (Y405F) was performed on glutamine synthesis gene, recombinant C. glutamicum overexpressing the mutated gene glnA′ was able to produce l-glutamine effectively. Co-expression of vgb and glnA′ genes in C. glutamicum produced 17 g/l l-glutamine in shake flask culture, approximately 30% more than that produced by the recombinant harboring only glnA′ gene. In fermentor cultivation, the recombinant yielded 25% more cells and produced 40.5 g/l l-glutamine. In this study, it was clearly demonstrated that VHb significantly enhanced cell growth, l-glutamate, and l-glutamine production by recombinant C. glutamicum. 相似文献
18.
Chen H Chu J Zhang S Zhuang Y Qian J Wang Y Hu X 《Applied microbiology and biotechnology》2007,74(6):1205-1212
To develop an efficient way to produce S-adenosylmethionine (SAM), methionine adenosyltransferase gene (mat) from Streptomyces spectabilis and Vitreoscilla hemoglobin gene (vgb) were coexpressed intracellularly in Pichia pastoris, both under control of methanol-inducible promoter. Expression of mat in P. pastoris resulted in about 27 times higher specific activity of methionine adenosyltransferase (SMAT) and about 19 times higher SAM
production relative to their respective control, suggesting that overexpression of mat could be used as an efficient method for constructing SAM-accumulating strain. Under induction concentration of 0.8 and 2.4%
methanol, coexpression of vgb improved, though to different extent, cell growth, SAM production, and respiratory rate. However, the effects of VHb on SAM
content (specific yield of SAM production) and SMAT seemed to be methanol concentration-dependent. When cells were induced
with 0.8% methanol, no significant effects of VHb expression on SAM content and specific SMAT could be detected. When the
cells were induced with 2.4% methanol, vgb expression increased SAM content significantly and depressed SMAT remarkably. We suggested that under our experimental scheme,
the presence of VHb might improve ATP synthesis rate and thus improve cell growth and SAM production in the recombinant P. pastoris. 相似文献
19.
Chung JW Webster DA Pagilla KR Stark BC 《Journal of industrial microbiology & biotechnology》2001,27(1):27-33
Using the pUT-miniTn5 vector system developed by the laboratory of K.N. Timmis, the Vitreoscilla hemoglobin gene (vgb) was integrated into the chromosomes of Pseudomonas aeruginosa and Burkholderia cepacia; Vitreoscilla hemoglobin (VHb) was expressed at 8.8 and 0.8 nmol/g wet weight of cells in the respective engineered strains. The vgb-bearing P. aeruginosa outgrew wild-type P. aeruginosa and degraded benzoic acid faster than the latter strain at both normal and low aeration. In contrast, the vgb-bearing B. cepacia strain had a growth advantage over the wild-type strain at ca. 90 ppm, but not at ca. 120 ppm 2,4-dinitrotoluene (DNT); no
difference in DNT degradation was seen between the two strains at either normal or low aeration. The results demonstrate the
practicality of enhancing bioremediation with vgb stably integrated into the chromosome, but also suggest that a minimal level of VHb expression is required for its beneficial
effects to be seen. Journal of Industrial Microbiology & Biotechnology (2001) 27, 27–33.
Received 20 October 2000/ Accepted in revised form 04 May 2001 相似文献
20.
A series of high-copy-number Escherichia coli expression vectors equipped with an oxygen-sensitive promoter Pvgb of Vitreoscilla hemoglobin (encoded by the vgb gene) were constructed and characterized. Plasmid pKVp containing Pvgb was inducible by low oxygen tension, while plasmid pKVpP containing a partition (par) region from plasmid pSC101 ligated to Pvgb provided inheritable stability for the vectors in the absence of ampicillin. Plasmid pKVpV had the Vitreoscilla hemoglobin operon vgb ligated to Pvgb, while a construct containing Pvgb, the vgb operon and a par region constituted plasmid pKVpPV. Shake-flask studies demonstrated that plasmids pKVpV and pKVpPV expressed higher levels of Vitreoscilla hemoglobin under low aeration condition (5% air saturation in water) compared with the levels observed under strong aeration (20% air saturation in water). Introduction of either the enhanced green fluorescent protein (eGFP) gene egfp or the toluene dioxygenase (TDO) gene tod into either pKVpV (Pvgb, vgb operon) or pKVpPV (Pvgb, vgb operon, par) slightly attenuated (30%) the strong expression of VHb under low aeration. However, all displayed approximately a three-fold increase versus that observed for strong aeration. Recombinant E. coli harboring either pKVp-E (Pvgb, egfp) or pKVpP-E (Pvgb, par, egfp) displayed at least a two-fold increase in eGFP expression under conditions of low aeration and absence of antibiotic, compared with that under strong aeration after 24 h of cultivation. Strong expression of TDO was also observed using low aeration in recombinant E. coli harboring pKVpPV-T (Pvgb, vgb operon, par, tod) or pKVpP-T (Pvgb, par, tod). Plasmids containing the par region were stable over 100 generations. These results indicate that the novel expression system combining plasmid stability over the cell growth phase and a promoter inducible by low oxygen tension will be very useful for high-density production of foreign proteins. 相似文献