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1.
Methee Khamduang Kanoktip Packdibamrung Jarun Chutmanop Yusuf Chisti Penjit Srinophakun 《Journal of industrial microbiology & biotechnology》2009,36(10):1267-1274
The production of l-phenylalanine is conventionally carried out by fermentations that use glucose or sucrose as the carbon source. This work
reports on the use of glycerol as an inexpensive and abundant sole carbon source for producing l-phenylalanine using the genetically modified bacterium Escherichia coli BL21(DE3). Fermentations were carried out at 37°C, pH 7.4, using a defined medium in a stirred tank bioreactor at various
intensities of impeller agitation speeds (300–500 rpm corresponding to 0.97–1.62 m s−1 impeller tip speed) and aeration rates (2–8 L min−1, or 1–4 vvm). This highly aerobic fermentation required a good supply of oxygen, but intense agitation (impeller tip speed
~1.62 m s−1) reduced the biomass and l-phenylalanine productivity, possibly because of shear sensitivity of the recombinant bacterium. Production of l-phenylalanine was apparently strongly associated with growth. Under the best operating conditions (1.30 m s−1 impeller tip speed, 4 vvm aeration rate), the yield of l-phenylalanine on glycerol was 0.58 g g−1, or more than twice the best yield attainable on sucrose (0.25 g g−1). In the best case, the peak concentration of l-phenylalanine was 5.6 g L−1, or comparable to values attained in batch fermentations that use glucose or sucrose. The use of glycerol for the commercial
production of l-phenylalanine with E. coli BL21(DE3) has the potential to substantially reduce the cost of production compared to sucrose- and glucose-based fermentations. 相似文献
2.
In this study, the effects of citrate addition on d-ribose production were investigated in batch culture of a transketolase-deficient strain, Bacillus subtilis EC2, in shake flasks and bioreactors. Batch cultures in shake flasks and a 5-l reactor indicated that supplementation with
0.2–0.5 g l−1 of citrate enhanced d-ribose production. When B. subtilis EC2 was cultivated in a 15-l reactor in a complex medium, the d-ribose concentration was 70.9 g l−1 with a ribose yield of 0.497 mol mol−1. When this strain was grown in the same medium supplemented with 0.3 g l−1 of citrate, 83.4 g l−1 of d-ribose were obtained, and the ribose yield was increased to 0.587 mol mol−1. Addition of citrate reduced the activities of pyruvate kinase and phosphofructokinase, while it increased those of glucose-6-phosphate
dehydrogenase and 6-phosphogluconate dehydrogenase. Metabolic flux distribution in the stationary phase indicated that citrate
addition resulted in increased fluxes in the pentose phosphate pathway and TCA cycle, and decreased fluxes in the glycolysis
and acetate pathways. 相似文献
3.
An acetate-negative mutant of Yarrowia lipolytica Wratislavia K1 was selected that, when grown with 300 g raw glycerol l−1 at pH 3, produced 170 g erythritol l−1 after 7 days, corresponding to a 56% yield and a productivity of 1 g l−1 h−1. The Wratislavia K1 strain did not produce citric acid. 相似文献
4.
Jin Zhou Ju Chu Yong-Hong Wang Si-Liang Zhang Ying-Ping Zhuang Zhong-Yi Yuan 《World journal of microbiology & biotechnology》2008,24(6):789-796
An intracellular S-adenosylmethionine synthetase (SAM-s) was purified from the fermentation broth of Pichia pastoris GS115 by a sequence chromatography column. It was purified to apparent homogeneity by (NH4)2SO4 fractionation (30–60%), anion exchange, hydrophobic interaction, anion exchange and gel filtration chromatography. HPLC showed
the purity of purified SAM-s was 91.2%. The enzyme was purified up to 49.5-fold with a final yield of 20.3%. The molecular
weight of the homogeneous enzyme was 43.6 KDa, as determined by electro-spray ionization mass spectrometry (ESI-MS). Its isoelectric
point was approximately 4.7, indicating an acidic character. The optimum pH and temperature for the enzyme reaction were 8.5
and 35 °C, respectively. The enzyme was stable at pH 7.0–9.0 and was easy to inactivate in acid solution (pH ≤ 5.0). The temperature
stability was up to 45 °C. Metal ions, such as, Mn2+ and K+ at the concentration of 5 mM had a slight activation effect on the enzyme activity and the Mg2+ activated the enzyme significantly. The enzyme activity was strongly inhibited by heavy metal ions (Cu2+ and Ag2+) and EDTA. The purified enzyme from the transformed Pichia pastoris synthesized S-adenosylmethionine (SAM) from ATP and l-methionine in vitro with a K
m of 120 and 330 μM and V
max of 8.1 and 23.2 μmol/mg/min for l-methionine and ATP, respectively. 相似文献
5.
Plant gum as an elicitor for guggulsterone production in cell cultures of Commiphora wightii is reported for the first time. Guggulsterone production increased 2.4 fold in the cell cultures by gum Arabic (100 mg l−1), while mesquite gum elicited 2 fold. The cells treated with gum Arabic at 7th and 9th day accumulated enhanced guggulsterones
within 24 h, which increased further up to 48 h and then declined. The cells treated at 9th day accumulated higher amount
(218 μg l−1) of guggulsterones after 48 h of elicitation as compared to cells treated at 7th day (164 μg l−1). The optimized elicitation conditions were used in vessels of varying capacity where maximum yield of 285 μg l−1 of guggulsterones was recorded in 3 l shake flasks. These experiments enabled highest guggulsterones yield in a short duration
of 11 days in cell cultures of C. wightii. 相似文献
6.
Bacillus coagulans has been of great commercial interest over the past decade owing to its strong ability of producing optical pure l-lactic acid from both hexose and pentose sugars including l-arabinose with high yield, titer and productivity under thermophilic conditions. The l-arabinose isomerase (L-AI) from Bacillus coagulans was heterologously over-expressed in Escherichia coli. The open reading frame of the L-AI has 1,422 nucleotides encoding a protein with 474 amino acid residues. The recombinant
L-AI was purified to homogeneity by one-step His-tag affinity chromatography. The molecular mass of the enzyme was estimated
to be 56 kDa by SDS-PAGE. The enzyme was most active at 70°C and pH 7.0. The metal ion Mn2+ was shown to be the best activator for enzymatic activity and thermostability. The enzyme showed higher activity at acidic
pH than at alkaline pH. The kinetic studies showed that the K
m, V
max and k
cat/K
m for the conversion of l-arabinose were 106 mM, 84 U/mg and 34.5 mM−1min−1, respectively. The equilibrium ratio of l-arabinose to l-ribulose was 78:22 under optimal conditions. l-ribulose (97 g/L) was obtained from 500 g/l of l-arabinose catalyzed by the enzyme (8.3 U/mL) under the optimal conditions within 1.5 h, giving at a substrate conversion
of 19.4% and a production rate of 65 g L−1 h−1. 相似文献
7.
Guo T Tang Y Zhang QY Du TF Liang DF Jiang M Ouyang PK 《Journal of industrial microbiology & biotechnology》2012,39(3):401-407
Clostridium beijerinckii mutant strain IB4, which has a high level of inhibitor tolerance, was screened by low-energy ion implantation and used for
butanol fermentation from a non-detoxified hemicellulosic hydrolysate of corn fiber treated with dilute sulfuric acid (SAHHC).
Evaluation of toxicity showed C. beijerinckii IB4 had a higher level of tolerance than parent strain C. beijerinckii NCIMB 8052 for five out of six phenolic compounds tested (the exception was vanillin). Using glucose as carbon source, C. beijerinckii IB4 produced 9.1 g l−1 of butanol with an acetone/butanol/ethanol (ABE) yield of 0.41 g g−1. When non-detoxified SAHHC was used as carbon source, C. beijerinckii NCIMB 8052 grew well but ABE production was inhibited. By contrast, C. beijerinckii IB4 produced 9.5 g l−1 of ABE with a yield of 0.34 g g−1, including 2.2 g l−1 acetone, 6.8 g l−1 butanol, and 0.5 g l−1 ethanol. The remarkable fermentation and inhibitor tolerance of C. beijerinckii IB4 appears promising for ABE production from lignocellulosic materials. 相似文献
8.
Xuefeng Wu Shaotong Jiang Mo Liu Lijun Pan Zhi Zheng Shuizhong Luo 《Journal of industrial microbiology & biotechnology》2011,38(4):565-571
Semicontinuous fermentation using pellets of Rhizopus oryzae has been recognized as a promising technology for l-lactic acid production. In this work, semicontinuous fermentation of R. oryzae AS 3.819 for l-lactic acid production has been developed with high l-lactic acid yield and volumetric productivity. The effects of factors such as inoculations, CaCO3 addition time, and temperature on l-lactic acid yield and R. oryzae morphology were researched in detail. The results showed that optimal fermentation conditions for the first cycle were: inoculation
with 4% spore suspension, CaCO3 added to the culture medium at the beginning of culture, and culture temperature of 32–34°C. In orthogonal experiments, high
l-lactic acid yield was achieved when the feeding medium was (g/l): glucose, 100; (NH4)2SO4, 2; KH2PO4, 0.1; ZnSO4·7H2O, 0.33; MgSO4·7H2O, 0.15; CaCO3, 50. Twenty cycles of semicontinuous fermentation were carried out in flask culture. l-lactic acid yield was 78.75% for the first cycle and 80–90% for the repeated cycles; the activities of lactate dehydrogenases
(LDH) were 7.2–9.2 U/mg; fermentation was completed in 24 h for each repeated cycle. In a 7-l magnetically stirred fermentor,
semicontinuous fermentation lasted for 25 cycles using pellets of R. oryzae AS 3.819 under the optimal conditions determined from flask cultures. The final l-lactic acid concentration (LLAC) reached 103.7 g/l, and the volumetric productivity was 2.16 g/(l·h) for the first cycle;
in the following 19 repeated cycles, the final LLAC reached 81–95 g/l, and the volumetric productivities were 3.40–3.85 g/(l·h). 相似文献
9.
Bilal Haider Abbasi Murad Khan Bin Guo Saleem Ahmed Bokhari Mir Ajab Khan 《Plant Cell, Tissue and Organ Culture》2011,105(3):337-344
The regeneration potential and antioxidative enzyme activities of economically important Brassica rapa var. turnip were evaluated. Calli were induced from leaf explants of seed-derived plantlets on Murashige and Skoog (MS) medium incorporated
with different concentrations of various plant growth regulators (PGRs). The highest leaf explant response (83%) was recorded
for 2.0 mg l−1 benzyladenine (BA) and 1.0 mg l−1 α-naphthaleneacetic acid (NAA). Subsequent subculturing of callus after 3 weeks of culture, on medium with similar compositions
of PGRs, induced shoot organogenesis. The highest shoot induction response (83%) was recorded for 5.0 mg l−1 BA after 5 weeks of transfer. However, 7.8 shoots/explant were recorded for 2.0 mg l−1 BA. The transferring of shoots to elongation medium resulted in 5.1-cm-long shoots on 10 mg l−1 of gibberellic acid (GA3). Rooted plantlets were obtained on MS medium containing different concentrations of indole butyric acid (IBA). The determination
of activities of antioxidative enzymes (superoxide dismutase [SOD], ascorbate peroxidase [APX], catalase [CAT], glutathione
peroxidase [GPX], and peroxidase [POD]) revealed involvement of these enzymes in callus formation and differentiation. All
of the activities were interlinked with each other and played significant roles in the scavenging of toxic free radicals.
This study will help in the advancement of a regeneration protocol for B. rapa var. turnip and the understanding of the functions of antioxidative enzymes in plant differentiation. 相似文献
10.
Hong-Sheng Wu Waseem Raza Dong-Yang Liu Cheng-Long Wu Ze-Shen Mao Yang-Chun Xu Qi-Rong Shen 《World journal of microbiology & biotechnology》2008,24(8):1297-1304
Watermelon production is threatened by fusarium wilt caused by Fusarium oxysporum f.sp. niveum (FON) in continuous cultivation system. Some elements, mainly allelochemicals, released from living roots or decayed plants
might be associated with the disease. The purpose of this work was to evaluate the possible impact of coumarin, one kind of
watermelon allelochemical, on FON. Furthermore, possible new mechanisms might be investigated during the ecological interactions
of plant-microbe. Results showed that coumarin strongly inhibited growth of FON leading to a decrease in its biomass, dry
weight of mycelia of FON in a liquid culture. The dry weight was decreased by 62.9% compared with control. The hyphal growth
of FON on plates was stopped at high (>400 mg l−1) concentrations of coumarin. At 320 mg l−1, sporulation and enzyme activities of FON were also severely suppressed by coumarin. The yield of conidia, and the activities
of proteinase, cellulase, and amylase were reduced by 98.9%, 79.7%, 29.8% and 15.9% respectively. However, conidial germination
and mycotoxin (MT) production of FON were greatly stimulated, being increased by 55.7% and 14.9 fold at 320 mg l−1 respectively. We conclude that coumarin acted as an allelochemical substance to inhibit growth and pathogenic enzyme activities
of FON but to stimulate mycotoxin production and conidial germination. It was suggested that coumarin acted as a signal transduction
element bridging plant and pathogen in the process of plant-microbe interactions. 相似文献
11.
Chang-Su Park Soo-Jin Yeom Yu-Ri Lim Yeong-Su Kim Deok-Kun Oh 《World journal of microbiology & biotechnology》2011,27(4):743-750
A putative ribose-5-phosphate isomerase (RpiB) from Streptococcus pneumoniae was purified with a specific activity of 26.7 U mg−1 by Hi-Trap Q HP anion exchange and Sephacryl S-300 HR 16/60 gel filtration chromatographies. The native enzyme existed as
a 96-kDa tetramer with activity maxima at pH 7.5 and 35°C. The RpiB exhibited isomerization activity with l-lyxose, l-talose, d-gulose, d-ribose, l-mannose, d-allose, l-xylulose, l-tagatose, d-sorbose, d-ribulose, l-fructose, and d-psicose and exhibited particularly high activity with l-form monosaccharides such as l-lyxose, l-xylulose, l-talose, and l-tagatose. With l-xylulose (500 g l−1) and l-talose (500 g l−1) substrates, the optimum concentrations of RpiB were 300 and 600 U ml−1, respectively. The enzyme converted 500 g l−1
l-xylulose to 350 g l−1
l-lyxose after 3 h, and yielded 450 g l−1
l-tagatose from 500 g l−1
l-talose after 5 h. These results suggest that RpiB from S. pneumoniae can be employed as a potential producer of l-form monosaccharides. 相似文献
12.
Xylose reductase (XR) is a key enzyme in biological xylitol production, and most XRs have broad substrate specificities. During
xylitol production from biomass hydrolysate, non-specific XRs can reduce l-arabinose, which is the second-most abundant hemicellulosic sugar, to the undesirable byproduct arabitol, which interferes
with xylitol crystallization in downstream processing. To minimize the flux from l-arabinose to arabitol, the l-arabinose-preferring, endogenous XR was replaced by a d-xylose-preferring heterologous XR in Candida tropicalis. Then, Bacillus licheniformis
araA and Escherichia coli araB and araD were codon-optimized and expressed functionally in C. tropicalis for the efficient assimilation of l-arabinose. During xylitol fermentation, the control strains BSXDH-3 and KNV converted 9.9 g l-arabinose l−1 into 9.5 and 8.3 g arabitol l−1, respectively, whereas the recombinant strain JY consumed 10.5 g l-arabinose l−1 for cell growth without forming arabitol. Moreover, JY produced xylitol with 42 and 16% higher productivity than BSXDH-3
and KNV, respectively. 相似文献
13.
A. Karthikeyan J. Shilpha S. Karutha Pandian M. Ramesh 《Plant Cell, Tissue and Organ Culture》2012,109(1):153-165
A reproducible and highly efficient protocol for Agrobacterium tumefaciens-mediated transformation of indica rice (Oryza sativa L. subsp. indica cv. ADT 43) was established. Prior to transformation, embryogenic callus were induced from mature seeds incubated on Linsmaier
and Skoog (LS) medium supplemented with 2.5 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.0 mg l−1 thiamine-HCl. Callus, intact mature seeds, and other in vitro derived explants (leaf bases, leaf blades, coleoptiles, and
root-tips) were immersed in a bacterial suspension culture of A. tumefaciens strain EHA 105, OD600 of 0.8, and co-cultivated on LS medium for 2 days in the dark at 25 ± 2°C. Based on GUS expression
analysis, 10 min incubation time of explants on a co-cultivation medium containing 100 μM acetosyringone was optimum. Following
β-glucuronidase (GUS) assay and polymerase chain reaction (PCR) analysis, transformants were identified. Stable integration
of the transgene was confirmed in four putatively transformed T0 plants by Southern blot analysis. The copy number of the transgene in these lines, one to two, was then determined. Among
the observations made, necrosis of co-cultivated explants was a problem, as well as sensitivity of callus to Agrobacterium infection. Levels of necrosis could be minimized following co-cultivation of explants in a medium consisting of 30% LS and
containing 10 g l−1 (14), polyvinyl pyrrolidone, 10% coconut water, and 250 mg l−1 timentin (15:1). This latter medium also increased the final transformation efficiency to 15.33%. 相似文献
14.
Fuhong Xie Yapeng Chao Zhiquan Xue Xiuqing Yang Guoqing Zhang Jiaji Shi Shijun Qian 《Journal of industrial microbiology & biotechnology》2009,36(5):739-746
In industry, fosfomycin is mainly prepared via chemical epoxidation of cis-propenylphosphonic acid (cPPA). The conversion yield of fosfomycin is less than 50% in the whole process and a large quantity
of waste is produced. Biotransformation by microorganisms is an alternative method of preparation. This kind of conversion
is more delicate, environmentally friendly, and the conversion yield of fosfomycin would be higher. In this work, an aerobic
bacterium capable of transforming cPPA to fosfomycin was isolated. The organism, designated as strain S101, was identified
as Bacillus simplex by morphological and physiological characteristics as well as by analysis of the gene encoding the 16S rRNA. Fosfomycin was
assayed by two means, bioassay and gas chromatography (GC). Glycerol was a good carbon source for growth and cPPA conversion
of strain S101. When cPPA was used as the sole carbon source, neither growth nor conversion to fosfomycin occurred. The optimum
cPPA concentration in the conversion medium was 2,000 μg ml−1. After 6 days of incubation, the concentration of fosfomycin reached its maximum level (1,838.2 μg ml−1), with a conversion ratio of 81.3%. Air was indispensable for the growth but not for the conversion to fosfomycin. Furthermore,
vanadium ions were found to be essential for the conversion. High concentrations of cPPA had fewer inhibitory effects on the
growth of strain S101. 相似文献
15.
Succinic acid, a four-carbon diacid, has been the focus of many research projects aimed at developing more economically viable
methods of fermenting sugar-containing natural materials. Succinic acid fermentation processes also consume CO2, thereby potentially contributing to reductions in CO2 emissions. Succinic acid could also become a commodity used as an intermediate in the chemical synthesis and manufacture
of synthetic resins and biodegradable polymers. Much attention has been given recently to the use of microorganisms to produce
succinic acid as an alternative to chemical synthesis. We have attempted to maximize succinic acid production by Actinobacillus succinogenes using an experimental design methodology for optimizing the concentrations of the medium components. The first experiment
consisted of a 24−1 fractional factorial design, and the second entailed a Central Composite Rotational Design so as to achieve optimal conditions.
The optimal concentrations of nutrients predicted by the model were: NaHCO3, 10.0 g l−1; MgSO4, 3.0 g l−1; yeast extract, 2.0 g l−1; KH2PO4. 5.0 g l−1; these were experimentally validated. Under the best conversion conditions, as determined by statistical analysis, the production
of succinic acid was carried out in an instrumented bioreactor using sugarcane bagasse hemicellulose hydrolysate, yielding
a concentration of 22.5 g l−1. 相似文献
16.
A genetic transformation system has been developed for callus cells of Crataegus
aronia using Agrobacterium
tumefaciens. Callus culture was established from internodal stem segments incubated on Murashige and Skoog (MS) medium supplemented with
5 mg l−1 Indole-3-butyric acid (IBA) and 0.5 mg l−1 6-benzyladenine (BA). In order to optimize the callus culture system with respect to callus growth and coloration, different
types and concentrations of plant growth regulators were tested. Results indicated that the best average fresh weight of red
colored callus was obtained on MS medium supplemented with 2 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.5 mg l−1 kinetin (Kin) (callus maintenance medium). Callus cells were co-cultivated with Agrobacterium harboring the binary plasmid pCAMBIA1302 carrying the mgfp5 and hygromycin phosphotransferase (hptII) genes conferring green fluorescent protein (GFP) activity and hygromycin resistance, respectively. Putative transgenic calli
were obtained 4 weeks after incubation of the co-cultivated explants onto maintenance medium supplemented with 50 mg l−1 hygromycin. Molecular analysis confirmed the integration of the transgenes in transformed callus. To our knowledge, this
is the first time to report an Agrobacterium-mediated transformation system in Crataegus
aronia. 相似文献
17.
Takashi Nemoto Taisuke Watanabe Yutaka Mizogami Jun-ichi Maruyama Katsuhiko Kitamoto 《Applied microbiology and biotechnology》2009,82(6):1105-1114
The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l−1 h−1, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition
strategy, which reached 8.46 ± 0.31 g l−1, 41.7 ± 1.4%, and 0.18 ± 0.01 g l−1 h−1 with the best continuous feeding strategy (0.2 g l−1 h−1), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L−1 h−1) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway
were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when
the l-Met feeding rate reached 0.5 g l−1 h−1. 相似文献
18.
19.
Two new effective microbial producers of inulinases were isolated from Jerusalem artichoke tubers grown in Thailand and identified
as Aspergillus niger TISTR 3570 and Candida
guilliermondii TISTR 5844. The inulinases produced by both these microorganisms were appropriate for hydrolysing inulin to fructose as the
principal product. An initial inulin concentration of ∼100 g l−1 and the enzyme concentration of 0.2 U g−1 of substrate, yielded 37.5 g l−1 of fructose in 20 h at 40°C when A. niger TISTR 3570 inulinase was the biocatalyst. The yield of fructose on inulin was 0.39 g g−1. Under identical conditions, the yeast inulinase afforded 35.3 g l−1 of fructose in 25 h. The fructose yield was 0.35 g g−1 of substrate. The fructose productivities were 1.9 g l−1 h−1 and 1.4 g l−1 h−1 for the mold and yeast enzymes, respectively. After 20 h of reaction, the mold enzyme hydrolysate contained 53% fructose
and more than 41% of initial inulin had been hydrolysed. Using the yeast enzymes, the hydrolysate contained nearly 38% fructose
at 25 h and nearly 36% of initial inulin had been hydrolysed. The A. niger TISTR 3570 inulinases exhibited both endo-inulinase and exo-inulinase activities. In contrast, the yeast inulinases displayed
mainly exo-inulinase activity. The mold and yeast crude inulinases mixed in the activity ratio of 5:1 proved superior to individual
crude inulinases in hydrolysing inulin to fructose. The enzyme mixture provided a better combination of endo- and exo-inulinase
activities than did the crude extracts of either the mold or the yeast individually. 相似文献
20.
Díaz-Barrera A Soto E Altamirano C 《Journal of industrial microbiology & biotechnology》2012,39(4):613-621
Alginates are polysaccharides that are used as thickening agents, stabilizers, and emulsifiers in various industries. These
biopolymers are produced by fermentation with a limited understanding of the processes occurring at the cellular level. The
objective of this study was to evaluate the effects of agitation rate and inlet sucrose concentrations (ISC) on alginate production
and the expression of the genes encoding for alginate-lyases (algL) and the catalytic subunit of the alginate polymerase complex (alg8) in chemostat cultures of Azotobacter vinelandii ATCC 9046. Increased alginate production (2.4 g l−1) and a higher specific alginate production rate (0.1 g g−1 h−1) were obtained at an ISC of 15 g l−1. Carbon recovery of about 100% was obtained at an ISC of 10 g l−1, whereas it was close to 50% at higher ISCs, suggesting that cells growing at lower sucrose feed rates utilize the carbon
source more efficiently. In each of the steady states evaluated, an increase in algL gene expression was not related to a decrease in alginate molecular weight, whereas an increase in the molecular weight of
alginate was linked to higher alg8 gene expression, demonstrating a relationship between the alg8 gene and alginate polymerization in A. vinelandii for the first time. The results obtained provide a possible explanation for changes observed in the molecular weight of alginate
synthesized and this knowledge can be used to build a recombinant strain able to overexpress alg8 in order to produce alginates with higher molecular weights. 相似文献