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1.
Methanogenic archaea are generally thought to use tetrahydromethanopterin or tetrahydrosarcinapterin (H4SPT) rather than tetrahydrofolate (H4F) as a pterin C1 carrier. However, the genome sequence of Methanosarcina species recently revealed a cluster of genes, purN, folD, glyA and metF, that are predicted to encode for H4F-specific enzymes. We show here for folD and glyA from M. barkeri that this prediction is correct: FolD (bifunctional N5,N10-methylene-H4F dehydrogenase/N5,N10-methenyl-H4F cyclohydrolase) and GlyA (serine:H4F hydroxymethyltransferase) were heterologously overproduced in Escherichia coli, purified and found to be specific for methylene-H4F and H4F, respectively (apparent Km below 5 M). Western blot analyses and enzyme activity measurements revealed that both enzymes were synthesized in M. barkeri. The results thus indicate that M. barkeri should contain H4F, which was supported by the finding that growth of M. barkeri was dependent on folic acid and that the vitamin could be substituted by p-aminobenzoic acid, a biosynthetic precursor of H4F. From the p-aminobenzoic acid requirement, an intracellular H4F concentration of approximately 5 M was estimated. Evidence is presented that the p-aminobenzoic acid taken up by the growing cells was not required for the biosynthesis of H4SPT, which was found to be present in the cells at a concentration above 3 mM. The presence of both H4SPT and H4F in M. barkeri is in agreement with earlier isotope labeling studies indicating that there are two separate C1 pools in these methanogens. 相似文献
2.
Satoshi Fukuzaki Naomichi Nishio Shiro Nagai 《Bioscience, biotechnology, and biochemistry》2013,77(9):2455-2460
Cobalt-free corrinoids (CFCs) were isolated from Methanosarcina barkeri Fusaro cells growing on a methanol minimum medium. The methanogen cells excreted a trace of CFCs (9.1 μg/I) into the culture medium when cobalt-deficient methanol medium was used. Several CFCs were separated by column chromatographies on ion exchangers and paper electrophoresis, where a major CFC showed a similar characteristic to that of nucleotide-free corrinoid, Factor B (cobinamide), suggesting to be hydrogenobinamide. By chemical insertion of Co2 +, Cu2 +, and Zn2+ into CFCs, the corresponding corrinoid and its metal analogues were observed. Bioassay using Escherichia coli 215 revealed that the major CFC (a yellow product obtained after alkaline treatment) and its copper and zinc analogues were inactive as cobalamin but were active as antimetabolites of cobalamin. However, the CFC greatly stimulated the cell growth of M. barkeri grown under cobalt-deficient conditions. 相似文献
3.
Summary Optimal growth of Methanosarcina barkeri occurred in a defined medium containing methanol when 2.5–4 mM sodium sulphide was added giving a concentration of 0.04–0.06 mM dissolved sulphide (HS–+S2–. When the sulphide concentration was too low for optimal growth (e.g., 0.1 mM Na2S added) the addition of the redox resin Serdoxit acted as a sulphide reservoir and caused a significant stimulation of growth. Furthermore it could be demonstrated that iron sulphide, zinc sulphide or L-methionine could also act as sulphur sources while the addition of sodium sulphate to sulphide-depleted media failed to restore growth. The amino acid L-cysteine (0.85 mM) stimulated growth but could not replace Na2S.Under optimal cysteine-and sulphide concentrations the generation time of this strain was about 7–9 h during growth on methanol, giving a growth yield of about 0.14 g/g methanol consumed. Different M. barkeri strains were also able to grow under these conditions on acetate (30–50 h doubling time) without a significant lag-phase and with complete substrate consumption even though the inoculum was grown on methanol or H2–CO2. When methanol and acetate were present as a mixture in the medium both were used simultaneously. 相似文献
4.
Tapan Kumar Mazumder Naomichi Nishio Satoshi Fukuzaki Shiro Nagai 《Applied microbiology and biotechnology》1987,26(6):511-516
Summary Production of vitamin B-12 compounds from methanol was carried out by Methanosarcina barkeri Fusaro, an anaerobic methanogen. The methanogen released about 40% to 70% of corrinoids irrespective of the culture medium
used. The use of cysteine instead of Na2S as the sole sulphur source for cell growth led to an increase in the cobalt chloride concentration in the culture medium
up to 16 times the normal (0.6 mg·l-1) without medium precipitation. This in turn resulted in an intracellular vitamin B-12 content of 5.6 mg·g dry cell-1, the rest being discharged into the culture supernatant; this was 87 mg·l-1, 73% of the total corrinoids after 20 repeated intermittently fed cultures and the final cell concentration was 5.8 g dry
cell·l-1. Taking advantage of this, continuous production of extracellular vitamin B-12 compounds was attempted with a fixed-bed bioreactor
(carrier: diatomaceous clay). At a steady state operation at space velocity of 9 to 11 day-1, the concentration of the discharged corrinoid was 6.8 to 7.9 mg·l-1, having a vitamin B-12 activity of about 4 mg·l-1. Total cell mass retained in the reactor was 39.6 g dry cell l-reactor-1. Identification of the corrinoids revealed that 19% of the total corrinoids was comprised of the vitamin B-12 Factor III
(5-hydroxybenzimidazolyl cobamide) and the remainder were mainly the base-free vitamin B-12 Factor B (cobinamide and its derivatives). 相似文献
5.
Factor F430 is a yellow compound of unknown structure present in methanogenic bacteria. It has recently been shown to contain nickel. In this communication the influence of the nickel concentration in the growth medium on the factor F430 content of Methanobacterium thermoautotrophicum and on the nickel content of factor F430 was studied. It was found: (1) The content of factor F430 in the cells was strongly dependent on the nickel concentration of the growth medium. Cells grown on media with 2.5 M NiCl2 contained 28 times as much factor F430 per g as those grown on media with 0.075 M NiCl2; (2) factor F430 was synthesized in nickel deprived cells only upon the addition of nickel Nickel uptake paralleled factor F430 synthesis; (3) independent of the nickel concentration in the growth medium, the extinction coefficient at 430 nm of factor F430 per mol nickel was always near 22,500 cm-1 (mol Ni)-1. These findings indicate that nickel is an essential component of factor F430.Dedicated to Professor Otto Kandler on the occasion of his 60th birthday 相似文献
6.
Pyruvate — a novel substrate for growth and methane formation in Methanosarcina barkeri 总被引:1,自引:0,他引:1
Methanosarcina barkeri strain Fusaro was found to grow on pyruvate as sole carbon and energy source after an incubation period of 10–12 weeks in the presence of high pyruvate concentrations (100 mM). Growth studies, cell suspension experiments and enzymatic investigations were performed with pyruvate-utilizing M. barkeri. For comparison acetate-adapted cells of M. barkeri were analyzed.
- Pyruvate-utilizing M. barkeri grew on pyruvate (100 mM) with an initial doubling time of about 25 h (37 °C, pH 6.5) up to cell densities of about 0.8 g cell dry weight/l. The specific growth rate was linearily dependent on the pyruvate concentration up to 100 mM indicating that pyruvate was taken up by passive diffusion. Only CO2 and CH4 were detected as fermentation products. As calculated from fermentation balances pyruvate was converted to CH4 and CO2 according to following equation: Pyruvate-+H++0.5 H2O » 1.25 CH4+1.75 CO2. The molar growth yield (Ych 4) was about 14 g dry weight cells/mol CH4. In contrast the growth yield (Ych 4) of M. barkeri during growth on acctate (Acetate-+H+ » CH4+CO2) was about 3 g/mol CH4.
- Cell suspensions of pyruvate-grown M. barkeri catalyzed the conversion of pyruvate to CH4, CO2 and H2 (5–15 nmol pyruvate consumed/min x mg protein). At low cell concentrations (0.5 mg protein/ml) 1 mol pyruvate was converted to 1 mol CH4, 2 mol CO2 and 1 mol H2. At higher cell concentration less H2 and CO2 and more CH4 were formed due to CH4 formation from H2/CO2. The rate of pyruvate conversion was linearily dependent on the pyruvate concentration up to about 30 mM. Cell suspensions of acetate-grown M. barkeri also catalyzed the conversion of 1 mol pyruvate to 1 mol CH4, 2 mol CO2 and 1 mol H2 at similar rates and with similar affinity for pyruvate as pyruvate-grown cells.
- Cell extracts of both pyruvate-grown and acetate-grown M. barkeri contained pyruvate: ferredoxin oxidoreductase. The specific activity in pyruvate-grown cells (0.8 U/mg) was 8-fold higher than in acetate-grown cells (0.1 U/mg). Coenzyme F420 was excluded as primary electron acceptor of pyruvate oxidoreductase. Cell extracts of pyruvate-grown M. barkeri contained carbon monoxide dehydrogenase activity and hydrogenase activity catalyzing the reduction by carbon monoxide and hydrogen of both methylviologen and ferredoxin (from Clostridium).
7.
Alexei Yeliseev Peter Gärtner Ulrike Harms Dietmar Linder Rudolf K. Thauer 《Archives of microbiology》1993,159(6):530-536
Methanosarcina barkeri was recently shown to contain two cytoplasmic isoenzymes of methylcobalamin: coenzyme M methyltransferase (methyltransferase 2). Isoenzyme I predominated in methanol-grown cells and isoenzyme II in acetate-grown cells. It was therefore suggested that isoenzyme I functions in methanogenesis from methanol and isoenzyme II in methanogenesis from acetate. We report here that cells of M. barkeri grown on trimethylamine, H2/CO2, or acetate contain mainly isoenzyme II. These cells were found to have in common that they can catalyze the formation of methane from trimethylamine and H2, whereas only acetate-grown cells can mediate the formation of methane from acetate. Methanol-grown cells, which contained only low concentrations of isoenzyme II, were unable to mediate the formation of methane from both trimethylamine and acetate. These and other results suggest that isoenzyme II (i) is employed for methane formation from trimethylamine rather than from acetate, (ii) is constitutively expressed rather than trimethylamine-induced, and (iii) is repressed by methanol. The constitutive expression of isoenzyme II in acetate-grown M. barkeri can explain its presence in these cells. The N-terminal amino acid sequences of isoenzyme I and isoenzyme II were analyzed and found to be only 55% similar.Abbreviations H-S-CoM
coenzyme M or 2-mercaptoethane-sulfonate
- CH3-S-CoM
methyl-coenzyme M or 2(methylthio)-ethanesulfonate
- [Co]
cobalamin
- CH3-[Co]
methylcobalamin
- H4MPT
tetrahydromethanopterin
- CH3-H4MPT
N
5-methyltetrahydromethanopterin
- MT1
methyltransferase 1 or methanol: 5-hydroxybenzimidazolyl cobamide methyltransferase
- MT2
methyltransferase 2 or methylcobalamin: coenzyme M methyltransferase
- Mops
morpholinopropanesulfonate
- 1 U =
1 mol/min 相似文献
8.
Vitamin B-12 is released from the purified gastric intrinsic factor-[57Co]vitamin B-12 (intrinsic factor- [57Co]vitamin B-12) complex, when incubated with rat intestinal mucosa. Maximum specific activity for splitting the complex is localized in ileal brush border. Release of [57Co]vitamin B-12 is not due to its mere exchange during incubation with endogenous non-radioactive vitamin B-12. The splitting process has specific requirement for Ca2+ and ATP and it is thermolabile, time- as well as temperature-dependent. It is also inactivated by the presence of p-chloromercuribenzoate. Further, the vitamin B-12-releasing factor has been isolated from solubilized brush border and is purified 70-fold by (NH4)2SO4 precipitation, gel filtration and Con. A-Sepharose 4B affinity chromatography. In SDS-polyacrylamide gel electrophoresis, it is resolved into a single band of about 25 kDa, indicating its purity. The releasing factor exhibits maximum activity at pH 7.4; isoelectric focusing reveals only one major form with pI 7.52. With intrinsic factor-[57Co]vitamin B-12-complex as the substrate, apparent Km and Vmax values obtained are 128.2·10−12 M/1 and 117.6 pg·h−1 100 μg protein, respectively. Amino acid and carbohydrate analyses reveal the glycoprotein nature of the factor. Intrinsic factor-[57Co]vitamin B-12 complex is not susceptible to unspecific proteolytic digestion/ Similarly, the releasing factor does not hydrolyse other proteins. Thus, the observed substrate-specificity of the releasing factor differentiates it from other known proteolytic enzymes of ileal brush borders. 相似文献
9.
Spontaneous Disaggregation of Methanosarcina mazei S-6 and Its Use in the Development of Genetic Techniques for Methanosarcina spp 总被引:6,自引:4,他引:2
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Jane E. Harris 《Applied microbiology》1987,53(10):2500-2504
When monomethylamine was the growth substrate, spontaneous disaggregation of Methanosarcina mazei S-6 commenced at the mid-exponential phase and resulted in the formation of a suspension containing 108 to 109 free cells per ml. Free cells were osmotically fragile and amenable to extraction of DNA. Hypertonic media for the manipulation and regeneration of free cells into aggregates were developed, and plating efficiencies of 100% were achieved for M. mazei S-6 and LYC. Free cells of strain S-6 required MgCl2 (10 mM) for growth, whereas aggregates did not. Specific growth rates of strains S-6 and LYC were increased by MgCl2. Treatment with pronase caused sphere formation and removal of the protein wall of cells of strain S-6, but protoplasts could not be regenerated. The disaggregating enzyme produced by strain S-6 facilitated the preparation of suspensions of free cells of some strains of Methanosarcina barkeri. Although this provided a means of extracting high-molecular-weight DNA from M. barkeri, less than 0.1% of free cells were viable. 相似文献
10.
K. C. ENGVILD 《Physiologia plantarum》1974,32(4):390-393
Suspension cultures of Datura innoxia Mill, were successfully grown on a modified Murashige and Skoog medium with 2,4–D, NAA or BAP as growth substances, provided the micronutrient levels were reduced to 1/10. Normal amounts of micronutrients were toxic. Attempts to identify the toxic elements did not succeed. Cultures grew exponentially on a shaker at 27°C in the light. Their doubling times varied from 1.1 days on 2,4–D (10–6M) or NAA (10?5M)+ 1 g/1 casein hydrolysate to 2.7 days on BAP (3 × 10?7M) and 5.1 days on supraoptimal levels of 2,4-D (10?5M). Cultures grew on NH4+-N alone (from ammonium malate) or on NO3?-N alone. Dry weight yield was proportional to the amount of nitrate-N added (47 mg/mg N). Filtered suspension cultures containing single cells (plating cultures) could be grown in agar in petri dishes when NAA or 2,4-D were used as growth substances. Cells grew at densities above 500 units/ml in the agar. Most colonies grew from cell aggregates but division in single cells was observed. The highest plating efficiency was about 50% on 10?6 M 2,4-D + 1 g/1 casein hydrolysate. 相似文献
11.
Summary A preliminary attempt was made for producing vitamin B-12 byMethanosarcina barkeri strain Fusaro in a fed-batch culture with a methanol minimum medium. After 11 days, total methanol consumption, cell density and corrinoid concentration were 145 g/l, 8.5 g(dry cell weight)/l, and 135 mg/l (73% in supernatant) respectively. Electrophoretic separation revealed that 33% of the total corrinoids was B-12 Factor III (5-hydroxybenzimidazolylcobamide) and the remaining corrinoids were cobinamide (Factor B) and its derivatives. 相似文献
12.
Methanosarcina barkeri was grown by acetate fermentation in complex medium (N2 gas phase). The molar growth yield was 1.6–1.9 g cells/mol methane formed. Under these conditions 63–82% of the methane produced byMethanosarcina strains was derived from the methyl carbon of acetate, indicating that some methane was derived from other media components. Growth was not demonstrated in complex media lacking acetate or mineral acetate medium containing acetate but lacking H2/CO2, methanol, or trypticase and yeast extract. Acetate metabolism byM. barkeri strain MS was further exmined in mineral acetate medium containing H2/CO2 and/or methanol, but lacking cysteine. Under these conditions, more methane was derived from the methyl carbon of acetate than from the carboxyl carbon. Methanogenesis from the methyl group increased with increasing acetate concentration. The methyl carbon contributed up to 42% of the methane formed with H2/CO2 and up to 5% with methanol. Methanol stimulated the oxidation of the methyl group of acetate to CO2. The average rates of methane formation from acetate were 1.3 nomol/min ·ml/culture (0.04mg2 cell dry weight) in defined media (gas phase H2/CO2) and complex media (gas phase N2). Acetate contributed up to 60% of cell carbon formed under the growth conditions examined. Similar quantities of cell carbon were derived from the methyl and carboxyl carbons of acetate, suggesting incorporation of this compound as a two-carbon unit. Incorporated acetate was not preferentially localized in lipid material, as 70% of the incorporated acetate was found in the wall and protein cell fractions. Acetate catabolism was stimulated by pregrowing of cultures in media containing acetate, while acetate anabolism was not influenced. The results are discussed in terms of the differences between the mechanisms of acetate catabolism and anabolism.Abbreviations CH3-S-CoM
methyl coenzyme M
- TCA
trichloroacetic acid
- CoM
coenzyme M (2-mercaptoethane sulfonic acid)
- Eo
standard potential change (pH 7)
- F420
Factor 420, a low redox electron carrier
- Go
standard free energy change (pH 7)
- kJ
kilojoules (=0.24 kilocalories)
- PBBW
Weimer's phosphate-buffered basal medium
- X
unknown C1 carrier 相似文献
13.
Lisbeth Fries 《Journal of phycology》1982,18(3):328-331
The marine brown alga Fucus spiralis L. and the red alga Goniotrichum alsidii (Zanard) increase their growth upon the, addition of SeO32- or SeO42- when cultivated axenically in the artificial seawater ASP6 F2. In the concentration range 1 · 10?10-1 · 10?7 M there are two optima, one at 3.3 · 10?10 M and another at 3.3 · 10?8 M. α-To-copherol, often administered together with selenium to mammals suffering from selenium deficiency, gives no additive effect with selenium, but α-tocopherol in the concentration range 1 × 10?7-1 × 10?6 M does influence the morphology of the Fucus plants. Organically bound selenium has no effect. 相似文献
14.
Brown trout were exposed for 63 days to five treatments: a control; the purified cyanobacterial hepatotoxin microcystin—LR (MC—LR) (41—57 μg MC—LR 1?1); lysed toxic Microcystis aeruginosa cells (41–68 μg MC—LR 1?1 and 288 μg chlorophyll a 1?1); lysed non—toxic M. aeruginosa cells (non—MC—LR containing and 288 μg chlorophyll a 1?1); ammonia (65–325 μg NH3 1?1). All treatments produced significantly reduced growth compared to controls (P<0·05, Fisher test). Exposure to ammonia resulted weight loss over the first 7 days followed by weight increase, though at a significantly lower level than in the other treatments. First exposed to lysed toxic M. aeruginosa cells grew less than those exposed to lysed non—toxic cyanobacteria or purified MC—LR. Sodium influx rates after 63 days exposure to purified MC—LR, lysed toxic M. aeruginosa cells, or ammonia showed a significant increase compared to control fish or those exposed to lysed non—toxic M. aeruginosa cells. There were no significant differences in Na+ efflux or net Na+ uptake rates between treatments. Significant increases in body Na+ and Cl— were seen in fish exposed to lysed toxic M. aeruginosa cells or ammonia. Only fish exposed to ammonia showed a significant increase in body ammonia. Short—term exposure, over 4 h, to lysed toxic cells, non—toxic cells or purified MC—LR resulted in insignificant changes in Na+ flux rates compared to controls although there was a significant net Na+ loss in fish exposed to ammonia. Chronic exposure of fish to toxic cyanobacterial blooms may result in ionic imbalance and reduced growth. 相似文献
15.
Corrinoids in several diverse species of methanogens were quantified by a bioassay utilizingEscherichia coli 113–3, a corrinoid auxotroph. All five species examined contained >0.65 nmol corrinoid/mg dry cells when grown on H2/CO2 as carbon and energy source. The highest corrinoid levels (4.1 nmol/mg cells) were found inMethanosarcina barkeri grown on methanol. The amount of corrinoids found in this species was dependent on growth conditions, but, regardless of
energy source, metabolized levels inMethanosarcina barkeri were higher than those found in theMethanobacterium species examined (M. arbophilicum, M. formicium, M. ruminantium, andM. thermoautotrophicum). 相似文献
16.
J. RUSSEL CAREFOOT 《The Journal of eukaryotic microbiology》1967,14(1):15-18
SYNOPSIS. Vitamin B12, biotin and thiamine requirements of 10 strains of Volvulina steinii and 1 strain of V. pringsheimii were studied. Vitamin B12 is required for growth of both species, thiamine stimulates growth slightly, and biotin has no discernible effect on growth. The minimum concentration of vitamin B12 giving a growth response in V. steinii, strain SC-2, was 10?8 g/ml, and maximum growth response was obtained with 1.1 × 10?7 g/ml. An organic carbon source is required for growth of V. steinii but not of V. pringsheimii. Growth of V. steinii, strain SC-2, occurred in 20 of 21 carbon sources tested. Optimal growth with each carbon source was largely dependent upon pH. Except for pyruvate, acetate, and ethanol, carbon source utilization was light-dependent, and growth in ethanol was reduced in the dark. Isocitric lyase activity was detected in V. steinii grown on acetate medium. 相似文献
17.
Kazutami Imai Tsuyoshi Sugio Takanori Tsuchida Tatsuo Tano 《Bioscience, biotechnology, and biochemistry》2013,77(7):1349-1354
Effect of heavy metal ions on the growth and the iron-oxidizing activity of Thiobacillus ferrooxidans were investigated.Cupric, zinc, cadmium, and chromium ions had no effect on the growth and the iron-oxidizing activity of cell suspensions or cell-free extracts of the bacterium in high concentrations (10?3~10?2M). Lead ion delayed the start of the growth slightly in 10?3 M, but it did not inhibit the iron-oxidizing activity of the cells in the concentration. Tin and molybdenum oxide ions inhibited both of them in the concentration above 10?3 M.Mercuric mercurous, and silver ions had the most harmful effect. In the concentration of 10?3 .M, each of the cations inhibited almost completely both the growth and the iron-oxidizing activity of the cells.In the experiments with cell-free extracts it was observed that the activity of cytochrome oxidase (cytochrome a597) operating in the iron-oxidizing system of the bacterium was specifically inhibited with mercuric ion in the concentration above 5 × 10?4 M. 相似文献
18.
Jacqueline M. Bentel David E. Lebwohl Kevin J. Cullen Mark S. Rubin Neal Rosen John Mendelsohn Wilson H. Miller 《Journal of cellular physiology》1995,165(1):212-221
Retinoids are currently being tested for the treatment and prevention of several human cancers, including breast cancer. However, the anti-cancer and growth inhibitory mechanisms of retinoids are not well understood. All-trans retinoic acid (RA) inhibits the growth of the estrogen receptor-positive (ER+) breast cancer cell line, MCF-7, in a reversible and dose-dependent manner. In contrast, insulin-like growth factors (IGF-I,IGF-II) and insulin are potent stimulators of the proliferation of MCF-7 and several other breast cancer cell lines. Pharmacologic doses of RA (≤10?6M) completely inhibit IGF-I-stimulated MCF-7 cell growth. Published data suggest that the growth inhibitory action of RA on IGF-stimulated cell growth is linear and dose-dependent, similar to RA inhibition of unstimulated or estradiol-stimulated MCF-7 cell growth. Surprisingly, we have found that IGF-I or insulin-stimulated cell growth is increased to a maximum of 132% and 127%, respectively, by cotreatment with 10?7 M RA, and that 10?9–10?7 M RA increase cell proliferation compared to IGF-I or insulin alone. MCF-7 cells that stably overexpress IGF-II are also resistant to the growth inhibitory effects of 10?9–10?7 M RA. Treatment with the IGF-I receptor blocking antibody, αIR-3, restores RA-induced growth inhibition of IGF-I-treated or IGF-II-overexpressing MCF-7 cells, indicating that the IGF-I receptor is mediating these effects. IGFs cannot reverse all RA effects since the altered cell culture morphology of RA-treated cells is similar in growth-inhibited cultures and in IGF-II expressing clones that are resistant to RA-induced growth inhibition. These results indicate that RA action on MCF-7 cells is biphasic in the presence of IGF-I or insulin with 10?9–10?7 M RA enhancing cell proliferation and ≥ 10?6M RA causing growth inhibition. As IGF-I and IGF-II ligands are frequently detectable in breast tumor tissues, their potential for modulation of RA effects should be considered when evaluating retinoids for use in in vivo experimental studies and for clinical purposes. Additionally, the therapeutic use of inhibitors of IGF action in combination with RA is suggested by these studies. © 1995 Wiley-Liss Inc. 相似文献
19.
O. Hadas R. Pinkas N. Malinsky-Rushansky G. Shalev-Alon E. Delphine T. Berner 《欧洲藻类学杂志》2013,48(2):259-267
Response of Aphanizomenon ovalisporum to certain environmental parameters was studied to gain a better understanding of the conditions which may have stimulated its autumnal bloom in Lake Kinneret. Optimal temperature for A. ovalisporum growth was 26–30?°C, resulting in growth rates of 0.2–0.3?day?1, similar to those observed in the lake. Maximal rate of CO2 fixation (assimilation numbers of 6–8?μg?C?μg?1?Chl?h?1) was obtained at low irradiances (I k of 40–100?μmol?photons?m?2?s?1), 200?μM Pi and low N:Pi ratios. Growth was strongly affected by phosphorus availability, reaching a maximum at Pi concentrations above 40?μM. The high demand for phosphorus was indicated by an increase in alkaline phosphatase activity. The relative abundance of Pi in the cells increased by 4-fold in Pi-rich compared with Pi-limited cultures. Uptake of Pi was faster in Pi-depleted compared with Pi-sufficient cells. Maximal photosynthetic rates and K1/2(HCO3 ?) were 140–220?μmol?O2?mg?1?Chl?h?1 and 10–24?μM, respectively. At pH 7.0 the K 1/2(CO2) was 2.2 and fell to 0.04?μM at pH 9.0. These data indicated that A. ovalisporum is a HCO3 ? user, and can explain its high photosynthetic rates during the bloom, under high pH and low dissolved CO2 conditions. Na+ concentrations of about 5?mM were essential for A. ovalisporum growth at high pH approaching values in the lake. 相似文献
20.
《Biocatalysis and Biotransformation》2013,31(1):34-38
AbstractThe effect of NADP+ and glucose-6-phosphate (G6P) on the biotransformation of D-xylose to xylitol by cells of Candida guilliermondii permeabilized with surfactant Triton X-100 was evaluated. The experimental runs were performed with 12 g L?1 of permeabilized cells and a reaction medium composed of Tris–HCl buffer (0.1 M pH 7), D-xylose (57 g L?1), and MgCl2.6H2O (5 mM). The levels of NADP+ (from 0.0 to 1.7 mM) and G6P (from 0.00 to 0.17 M) were varied according a 22-full factorial composed design. Under optimized conditions (NADP+ 0.5 mM and 0.05 M G6P), the xylitol volumetric productivity (QP) and yield factor (YP/S) predicted were 1.86 ± 0.03 g L?1 h? 1 and 0.64 ± 0.03 g g?1, respectively. These values were 94% and 19% higher than those obtained with unpermeabilized cells under fermentation conditions (0.97 g L?1 h?1 and 0.53 g g?1, respectively). On the basis of the results, it can be concluded that xylitol production by biotransformation with cells of C. guilliermondii permeabilized with Triton X-100 is a promising alternative to the fermentative process. 相似文献