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1.
Animal waste causes environmental problems like eutrophication of ground and surface water or the pollution of the atmosphere
because of its high NH4
+ content. The aim of our study was to fix the nitrogen of swine waste as biomass. Therefore, an isolated alga, Chlorella sp., and bacteria naturally living in liquid manure were grown in batch cultures (containing diluted swine waste supplied
with a nutrient solution) and continuous cultures (undiluted liquid manure) to achieve reduction of NH4
+ and total organic carbon (TOC) contents. For continuous cultivation, a photobioreactor of our own design was used. The batch
cultivation of Chlorella sp. and bacteria in swine waste resulted in good growth of both groups of organisms and in a reduction of 25% NH4
+ and 80% TOC. In the continuous cultivation a steady state was not achieved owing to a change in the composition of the bacterial
population. NH4
+ was totally removed, but NO2
− (up to 100 mM) was transiently released. NO3
− was not detected. These effects might be explained by the presence of heterotrophic nitrifiers, which are able to oxidize
NH4
+ to NO2
− and to reduce NO2
− to gaseous compounds.
Received: 21 January 1999 / Received revision: 9 March 1999 / Accepted: 14 March 1999 相似文献
2.
An alga known as “Nannochloropsis”, isolated from a prawn farm in Hainan, China, has been critically investigated and identified as Chlorella, a member of the Chlorophyceae based on fatty acid composition, ultrastructure, and 18S rDNA. Cells of this alga were spherical,
measured by 1–6 μm in diameter and were enclosed in thin walls of approximately 0.04 μm thickness. They contained several
small mitochondria, two to three thylakoids and had no vacuoles. There were many pyrenoids in the algal cells and their thylakoid
lamellae were sparse and not translucent. Many lipid droplets were present in the cytoplasm. The total lipid content of this
alga was 3% per gram dry weight and its major fatty acids were C16:0, C18:0, C18:1, C18:2, C18:3 and C20:0. Eicosapentaenoic acid (C20:5, EPA) was not detected. The length of its 18S rDNA sequence was 1,712 bp. 18S rDNA sequence analyses indicated that this
alga was a species of Chlorella. 相似文献
3.
Summary. The neurotoxicity of domoic acid was studied in 2–3 week old rat hippocampal slice cultures, derived from 7 day old rat pups.
Domoic acid 0.1–100 μM was added to the culture medium for 48 hrs, alone or together with the glutamate receptor antagonists NS-102 (5-Nitro-6,7,8,9-tetrahydrobenzo[G]indole-2,3-dione-3-oxime),
NBQX (2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline) or MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine
hydrogen maleate), followed by transfer of the cultures to normal medium for additional 48 hrs. Neuronal degeneration in the
fascia dentata (FD), CA3 and CA1 hippocampal subfields was monitored and EC50 values estimated by densitometric measurements of the cellular uptake of propidium iodide (PI). The CA1 region was most sensitive
to domoic acid, with an EC50 value of 6 μM domoic acid, estimated from the PI-uptake at 72 hrs. Protective effects of 10 μM NBQX against 3 and 10 μM domoic acid were observed for both dentate granule cells and CA1 and CA3c pyramidal cells. NS102 and MK 801 only displayed
protective effects when combined with NBQX. MK801 significantly increased the combined neuroprotective effect of NBQX and
NS102 against 10 μM domoic acid in both CA1 and FD, but not in CA3. We conclude, that domoic acid neurotoxicity in CA3 and in hippocampal slice
cultures in general primarily involves AMPA/kainate receptors. At high concentrations (10 μM domic acid) NMDA receptors are, however, also involved in the toxicity in CA1 and FD.
Received June 29, 2001 Accepted August 6, 2001 Published online June 3, 2002 相似文献
4.
Inhibition of photosynthesis by intracellular carbonic anhydrase in microalgae under excess concentrations of CO2 总被引:2,自引:0,他引:2
When cells of Chlorococcum littorale that had been grown in air (air-grown cells) were transferred to extremely high CO2 concentrations (>20%), active photosynthesis resumed after a lag period which lasted for 1–4 days. In contrast, C. littorale cells which had been grown in 5% CO2 (5% CO2-grown cells) could grow in 40% CO2 without any lag period. When air-grown cells were transferred to 40% CO2, the quantum efficiency of PS II (ΦII) decreased greatly, while no decrease in ΦII was apparent when the 5% CO2-grown cells were transferred to 40% CO2. In contrast to air-grown cells, 5% CO2-grown cells showed neither extracellular nor intracellular carbonic anhydrase (CA) activity. Upon the acclimation of 5% CO2-grown cells to air, photosynthetic susceptibility to 40% CO2 was induced. This change was associated with the induction of CA. In addition, neither suppression of photosynthesis nor
arrest of growth was apparent when ethoxyzolamide (EZA), a membrane-permeable inhibitor of CA, had been added before transferring
air-grown cells of C. littorale to 40% CO2. The intracellular pH value (pHi) decreased from 7.0 to 6.4 when air-grown C. littorale cells were exposed to 40% CO2 for 1–2 h, but no such decrease in pHi was apparent in the presence of EZA. Both air- and 5% CO2-grown cells of Chlorella sp. UK001, which was also resistant to extremely high CO2 concentrations, grew in 40% CO2 without any lag period. The activity of CA was much lower in air-grown cells of this alga than those in air-grown C. littorale cells. These results prompt us to conclude that intracellular CA caused intracellular acidification and hence inhibition
of photosynthetic carbon fixation when air-grown C. littorale cells were exposed to excess concentrations of CO2. No such harmful effect of intracellular CA was observed in Chlorella sp. UK001 cells.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
Sirisansaneeyakul S Singhasuwan S Choorit W Phoopat N Garcia JL Chisti Y 《Marine biotechnology (New York, N.Y.)》2011,13(5):928-941
The microalgae Chlorella protothecoides UTEX 25, Chlorella sp. TISTR 8991, and Chlorella sp. TISTR 8990 were compared for use in the production of biomass and lipids under photoautotrophic conditions. Chlorella sp. TISTR 8990 was shown to be potentially suitable for lipid production at 30°C in a culture medium that contained only
inorganic salts. For Chlorella sp. TISTR 8990 in optimal conditions in a stirred tank photobioreactor, the lipid productivity was 2.3 mg L−1 h−1 and after 14 days the biomass contained more than 30% lipids by dry weight. To attain this, the nitrogen was provided as
KNO3 at an initial concentration of 2.05 g L−1 and chelated ferric iron was added at a concentration of 1.2 × 10−5 mol L−1 on the ninth day. Under the same conditions in culture tubes (36 mm outer diameter), the biomass productivity was 2.8-fold
greater than in the photobioreactor (0.125 m in diameter), but the lipid productivity was only 1.2-fold higher. Thus, the
average low-light level in the photobioreactor actually increased the biomass specific lipid production compared to the culture
tubes. A light-limited growth model closely agreed with the experimental profiles of biomass production, nitrogen consumption,
and lipid production in the photobioreactor. 相似文献
6.
Batch cultures of the green microalga Chlorella vulgaris and cyanobacterium Planktothrix isothrix and their corresponding co-cultures were grown in municipal wastewater in order to study their growth as well as the nitrogen
(NH4–N) and phosphorus (PO43−–P) removal. The cultures were grown under two irradiances of 20 and 60 μmol photons m−2 s−1 in shaken and unshaken conditions. The co-culture of unshaken Chlorella and Planktothrix showed the greatest growth under both irradiances. The monoalgal Planktotrix cultures showed better growth when unshaken than when shaken, whereas Chlorella cultures grew better when mixed, but only at the higher irradiance. The highest percentage of nitrogen removal (up to 80%)
was attained by the unshaken co-cultures of Chlorella and Planktothrix. The amount of nitrogen recycled in the biomass reached up to 85% of that removed. Shaken monoalgal cultures of Chlorella showed phosphorus removal under both irradiances. They completely removed the initial phosphorus concentration (7.47 ± 0.17 mg L−1) within 96 and 48 h under 20 and 60 μmol photons m−2 s−1, respectively. 相似文献
7.
An extracellular β-agarase (AgaA34) was purified from a newly isolated marine bacterium, Agarivorans albus YKW-34 from the gut of a turban shell. AgaA34 was purified to homogeneity by ion exchange and gel filtration chromatographies
with a recovery of 30% and a fold of ten. AgaA34 was composed of a single polypeptide chain with the molecular mass of 50 kDa.
N-terminal amino acid sequencing revealed a sequence of ASLVTSFEEA, which exhibited a high similarity (90%) with those of
agarases from glycoside hydrolase family 50. The pH and temperature optima of AgaA34 were pH 8.0 and 40°C, respectively. It
was stable over pH 6.0–11.0 and at temperature up to 50°C. Hydrolysis of agarose by AgaA34 produced neoagarobiose (75 mol%)
and neoagarotetraose (25 mol%), whose structures were identified by matrix-assisted laser desorption ionization time-of-flight
mass spectroscopy and 13C NMR. AgaA34 cleaved both neoagarohexaose and neoagarotetraose into neoagarobiose. The k
cat/K
m values for hydrolysis agarose and neoagarotetraose were 4.04 × 103 and 8.1 × 102 s−1 M−1, respectively. AgaA34 was resistant to denaturing reagents (sodium dodecyl sulfate and urea). Metal ions were not required
for its activity, while reducing reagents (β-Me and dithiothreitol, DTT) increased its activity by 30%. 相似文献
8.
Mechanisms of inorganic carbon assimilation were investigated in the deep-water alga Phyllariopsis purpurascens (C. Agardh) Henry et South (Laminariales, Phaeophyta). The gross photosynthetic rate as a function of external pH, at a constant
concentration of 2 mM dissolved inorganic carbon (DIC), decreased sharply from pH 7.0 to 9.0, and was not substantially different
from 0 above pH 9.0. These data indicate that P. purpurascens is inefficient in the use of external HCO3
− as a carbon source in photosynthesis. Moreover, the photosynthetic rate as a function of external DIC and the highest pH
(9.01 ± 0.07) that this species can achieve in a closed system were consistent with a low capacity to use HCO3
−, in comparison to many other species of seaweeds. The role of external carbonic anhydrase (CA; EC 4.2.1.1) on carbon uptake
was investigated by measuring both the HCO3
−-dependent O2 evolution and the CO2 uptake, at pH 5.5 and 8.0, and the rate of pH change in the external medium, in the presence of selected inhibitors of extra-
and intracellular CA. Photosynthetic DIC-dependent O2 evolution was higher at pH 5.5 (where CO2 is the predominant form of DIC) than at pH 8.0 (where the predominant chemical species is HCO3
−). Both intra- and extracellular CA activity was detected. Dextran-bound sulfonamide (DBS; a specific inhibitor of extracellular
CA) reduced the photosynthetic O2 evolution and CO2 uptake at pH 8.0, but there was no effect at pH 5.5. The pH-change rate of the medium, under saturating irradiance, was reduced
by DBS. Phyllariopsis purpurascens has a low efficiency in the use of HCO3
− as carbon source in photosynthesis; nevertheless, the ion can be used after dehydration, in the external medium, catalyzed
by extracellular CA. This mechanism could explain why the photosynthetic rate in situ was higher than that supported solely
by the diffusion of CO2 from seawater.
Received: 6 March 1998 / Accepted: 22 June 1998 相似文献
9.
The response of Antarctic, tropical and temperate microalgae of similar taxonomic grouping to ultraviolet radiation (UVR)
stress was compared based on their growth and fatty acid profiles. Microalgae of similar taxa from the Antarctic (Chlamydomonas UMACC 229, Chlorella UMACC 237 and Navicula UMACC 231), tropical (Chlamydomonas augustae UMACC 246, Chlorella vulgaris UMACC 001 and Amphiprora UMACC 259) and temperate (Chlamydomonas augustae UMACC 247, Chlorella vulgaris UMACC 248 and Navicula incerta UMACC 249) regions were exposed to different UVR conditions. The cultures were exposed to the following conditions: PAR (42 μmol
photons m−2 s−1), PAR + UVA (854 μW cm−2) and PAR + UVA + UVB (117 μW cm−2). The cultures were subjected to UVA doses of 46.1, 92.2 and 184.4 J cm−2 and UVB doses of 6.3, 12.6 and 25.2 J cm−2 by varying the duration of their exposure (1.5, 3 and 6 h) to UVR during the light period (12:12 h light-dark cycle). UVA
did not affect the growth of the microalgae, even at the highest dose. In contrast, growth was adversely affected by UVB,
especially at the highest dose. The dose that caused 50% inhibition (ID50) in growth was used to assess the sensitivity of the microalgae to UVB. Sensitivity of the microalgae to UVB was species-dependent
and also dependent on their biogeographic origin. Of the nine microalgae, the Antarctic Chlorella was most tolerant to UVB stress (ID50 = 21.0 J cm−2). Except for this Chlorella, the percentage of polyunsaturated fatty acids of the microalgae decreased in response to high doses of UVB. Fatty acid profile
is a useful biomarker for UVB stress for some microalgae.
Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines. 相似文献
10.
U. Mukundan V. Bhide G. Singh W. R. Curtis 《Applied microbiology and biotechnology》1998,50(2):241-245
Brief exposure of Beta vulgaris root cultures to acidic medium resulted in release of betalain pigments while the capability for regrowth and continued pigment
accumulation was retained. A 10-min exposure to pH 2 followed by return to standard growth medium (pH 5.5, 1.1 mM PO4) resulted in release of 0.59 mg pigment/g dry weight over the subsequent 24-h period. The released pigment corresponds to
36.8% of the total pigments. Further improvement in culture productivity was achieved through phosphate limitation. Specific
pigment productivity increased fivefold for cultures grown in phosphate-free medium as compared to cultures grown in control
medium (1.1 mM PO4). A maximum total pigment production of 25.2 mg/l was observed at an initial medium phosphate level 0.3 mM. When combined
with phosphate limitation, low pH facilitated the release of 3.03 mg pigment/g dry weight, which corresponds to 50% of the
total pigment. The permeabilized roots were capable of regrowth and continued pigment accumulation. A cytochemical assay for
respiratory activity revealed that the basis of regrowth was lateral root initials that were unaffected during the acidic
pH treatment.
Received: 16 December 1997 / Received revision: 7 May 1998 / Accepted: 16 May 1998 相似文献
11.
Pier Giovanni Baraldi Mojgan Aghazadeh Tabrizi Francesca Fruttarolo Romeo Romagnoli Delia Preti 《Purinergic signalling》2009,5(1):3-19
Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named
A1, A2A, A2B and A3 (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding
of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective
agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview
of the recent advancements in identifying potent and selective A2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine
ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N
6-, C2-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions.
Compounds 1-deoxy-1-{6-[N′-(furan-2-carbonyl)-hydrazino]-9H-purin-9-yl}-N-ethyl-β-D-ribofuranuronamide (19, hA1
K
i = 1050 nM, hA2A
K
i = 1550 nM, hA2B EC50 = 82 nM, hA3
K
i > 5 μM) and its 2-chloro analogue 23 (hA1
K
i = 3500 nM, hA2A
K
i = 4950 nM, hA2B EC50 = 210 nM, hA3
K
i > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay
in Chinese hamster ovary (CHO) cells expressing hA2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide
(BAY-60–6583, hA1, hA2A, hA3 EC50 > 10 μM; hA2B EC50 = 3 nM) is currently under preclinical-phase investigation for treating coronary artery disorders and atherosclerosis.
This article has previously been published in issue 4/4, under doi:. 相似文献
12.
Fabrizio Briganti Stefano Mangani A. Scozzafava Guido Vernaglione Claudiu T. Supuran 《Journal of biological inorganic chemistry》1999,4(5):528-536
The interaction of human carbonic anhydrase (hCA) isozymes I and II with cyanamide, a linear molecule isoelectronic with
the main physiological substrate of the enzyme, CO2, was investigated through spectroscopic, kinetic, and X-ray crystallographic studies. We show here that cyanamide is hydrated
to urea in the presence of CAs, and that it also acts as a weak non-competitive inhibitor (K
I=61±3 mM and 238±9 mM for hCA II and hCA I, respectively) towards the esterasic activity of these enzymes, as tested with
4-nitrophenyl acetate. Changes in the spectrum of the Co(II)-hCA II derivative observed in the presence of cyanamide suggest
that it likely binds the metal ion within the CA active site, adding to the coordination sphere, not substituting the metal-bound
solvent molecule. It thereafter undergoes a nucleophilic attack from the metal-bound hydroxide ion, forming urea which remains
bound to the metal, as observed in the X-ray crystal structure of hCA II soaked in cyanamide solutions for several hours.
The urea molecule is directly coordinated to the active site Zn(II) ion through a protonated nitrogen atom. Several hydrogen
bonds involving active site residues Thr199 and Thr200 as well as three water molecules (Wat99, Wat122, and Wat123) further
stabilize the urea-hCA II adduct. Kinetic studies in solution further proved that urea acts as a tight binding inhibitor of
the two isozymes hCA I and hCA II, with very slow binding kinetics (k
on=2.5×10–5 s–1 M–1). A mechanism to explain the hydration process of cyanamide by CAs, as well as the tight binding of urea in the active site,
is also proposed based on the hypothesis that urea is deprotonated when bound to the enzyme. Cyanamide is thus the first true
suicide substrate of this enzyme for which binding has been documented by means of X-ray crystallographic and spectroscopic
studies.
Received: 26 February 1999 / Accepted: 25 May 1999 相似文献
13.
Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named
A1, A2A, A2B and A3 (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding
of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective
agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview
of the recent advancements in identifying potent and selective A2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine
ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N
6-, C2-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions.
Compounds 1-deoxy-1-{6-[N′-(furan-2-carbonyl)-hydrazino]-9H-purin-9-yl}-N-ethyl-β-D-ribofuranuronamide (19, hA1
K
i = 1050 nM, hA2A
K
i = 1550 nM, hA2B EC50 = 82 nM, hA3
K
i > 5 μM) and its 2-chloro analogue 23 (hA1
K
i = 3500 nM, hA2A
K
i = 4950 nM, hA2B EC50 = 210 nM, hA3
K
i > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay
in Chinese hamster ovary (CHO) cells expressing hA2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide
(BAY-60–6583, hA1, hA2A, hA3 EC50 > 10 μM; hA2B EC50 = 3 nM) is currently under preclinical-phase investigation for treating coronary artery disorders and atherosclerosis. 相似文献
14.
Carbonic anhydrase (CA) was purified from the unicellular green alga Chlamydomonas reinhardii, and the purity of the preparation was established by gradient gel electrophoresis. The purified enzyme exhibited a MW of 165 000 and contained 6 atoms of Zn. The subunit MW, as determined by dodecyl sulfate electrophoresis, was 27 000. These results are consistent with a quarternary structure which is hexameric, each monomer containing 1 g atom of Zn. Like spinach CA, and in contrast to other oligomeric plant CAs, a sulfhydryl reducing agent is not needed to stabilize the enzyme. CO2-hydrase activity was inhibited by both acetazolamide (I50 = 7.8 × 10?9M) and sulfanilamide (I50 = 1.3 × 10?5M), as well as by certain inorganic anions. The purified enzyme showed relatively weak esterase activity with p-nitrophenyl acetate but was an extremely effective esterase with 2-hydroxy-5-nitro-α-toluenesulfonic acid sultone as the substrate. Both esterase activities could be completely inhibited by adding acetazolamide. In its gross structural characteristics, the C. reinhardii enzyme resembles the CAs from higher plants. However, in its esterase activity and the inhibition by sulfonamides it is markedly different from plant CAs and bears more resemblance to erythrocyte CAs. 相似文献
15.
The permeability of biological membranes to boric acid was investigated using the giant internodal cells of the charophyte
alga Chara corallina (Klein ex Will. Esk. R.D. Wood). The advantage of this system is that it is possible to distinguish between membrane transport
of boron (B) and complexing of B by plant cell walls. Influx of B was found to be rapid, with equilibrium between the intracellular
and extracellular phases being established after approximately 24 h when the external concentration was 50 μM. The intracellular
concentration at equilibrium was 55 μM, which is consistent with passive distribution of B across the membrane along with
a small amount of internal complexation. Efflux of B occurred with a similar half-time to influx, approximately 3 h, which
indicates that the intracellular B was not tightly complexed. The concentration dependence of short-term influx measured with
10B-enriched boric acid was biphasic. This was tentatively attributed to the operation of two separate transport systems, a
facilitated system that saturates at 5 μM, and a linear component due to simple diffusion of B through the membrane. V
max and K
m for the facilitated transport system were 135 pmol m−2 s−1 and 2 μM, respectively. The permeability coefficient for boric acid in the Chara plasmalemma estimated from the slope of the linear influx component was 4.4 × 10−7 cm s−1 which is an order of magnitude lower than computed from the ether:water partition coefficient for B.
Received: 14 August 2000 / Accepted: 16 September 2000 相似文献
16.
In the green alga Chlorella vulgaris UAM 101, a CO2-concentrating mechanism (CCM) is induced when cells are transferred from high (5%) to low (0.03%) CO2 concentrations. The induction of the CCM is correlated with de-novo synthesis of several polypeptides that remain to be identified.
The internal carbonic anhydrase (CA; EC 4.2.1.1) activity increased 6- to 7-fold within 6 h of acclimation to air. When crude
homogenates were further separated into soluble and insoluble fractions, nearly all of the CA activity was associated with
the membrane fraction. Immunoblot analysis of cell homogenates probed with antibodies raised against the 37-kDa subunit of
periplasmic CA of Chlamydomonas reinhardtii showed a cross-reaction with a single 38-kDa polypeptide in both high- and low-CO2-grown cells. The up-regulation of the expression of the 38-kDa polypeptide was closely correlated with the increase in internal
CA activity. Furthermore, its subcellular location was also correlated with the distribution of the activity. Immunoblot analysis
of pyrenoid fractions showed that the 38-kDa polypeptide was concentrated in the pyrenoids from low-CO2-grown cells but was not present in pyrenoids from high-CO2-grown cells. In addition, immunogold labeling experiments showed that the protein was mainly associated with membranes crossing
the pyrenoid, while it was absent from the pyrenoid matrix. These studies have identified a putative intracellular CA polypeptide
associated with the pyrenoid in Chlorella vulgaris, suggesting that this structure may play an important role in the operation of the CCM and the acclimation to low CO2 conditions.
Received: 16 July 1997 / Accepted: 26 April 1998 相似文献
17.
Dithiothreitol (CH2SHCHOHCHOHCH2SH), under neutral conditions in aqueous medium, reacts readily and reversibly with vanadate to form longlived complexes.
The ligand, vanadium and proton stoichiometries were established from concentration and pH studies. The two predominant products
each contained two vanadium(V) nuclei and one dithiothreitol and carried an overall doubly negative charge. The equilibrium
shifted toward a triply negative charge with increase in pH through the pK
a range of the products. The 51V NMR spectra clearly showed two resonances for each product (–352 and –362 ppm for one and –399 and –526 ppm for the other),
thus establishing there are chemical differences in the coordination about each vanadium. A coordination scheme was proposed
for each product. The common motif proposed was the presence of a cyclic [VO]2 core as the source of a strong stabilizing interaction leading to the very favourable formation constants (overall about
107 at pH 7). The coordination shell about the individual vanadiums each contained one sulfur in the one product and one sulfur
about one vanadium and only oxygen about the other vanadium in the second product. Under neutral conditions the reduction
of V(V) to V(IV) requires in the order of 90 min. However, if hydrogen peroxide, in greater than a 2 : 1 molar ratio over
dithiothreitol, is included in the reaction medium, all the dithiothreitol is rapidly oxidized, and peroxovanadium(V) complexes
are observed. Addition of excess dithiothreitol regenerates the dithiothreitol/vanadate complexes.
Received: 2 May 1997 / Accepted: 2 July 1997 相似文献
18.
The yield and physicochemical properties of native and alkali treated carrageenan from Eucheuma isiforme harvested from the Nicaraguan coast were investigated. The native carrageenan yield was 57.2% of dry weight and decreased
to 43.5% when the alga was alkali treated. Native carrageenan viscosities showed significant differences between native (144.6 ± 3.3 cPs)
and treated carrageenan (113.9 ± 2.6 cPs) (p < 0.01). Alkali treatment reduced carrageenan sulphate content by 19.3% and increased 3,6 AG content by 13%. Alkali-treated
carrageenan formed very weak gels in 1.5% solutions (<50 g cm−2). Chemical analysis and FTIR spectra revealed that Eucheuma isiforme from Nicaragua is a good source of relatively pure iota-carrageenan with sufficient quality to serve as a substitute for
traditional iota-carrageenan sources. 相似文献
19.
T Roukas 《Journal of industrial microbiology & biotechnology》1999,22(6):617-621
Aureobasidium pullulans P56 was investigated using an adaptation technique and a mixed culture system. The adaptation of A. pullulans and the mixed cultures of A. pullulans and/or Lactobacillus brevisX20, Debaryomyces hansenii 194 and Aspergillus niger did not increase the production of polysaccharide. Enzymic hydrolysis of lactose in deproteinized whey gave a higher polysaccharide
concentration and polysaccharide yield than acidic hydrolysed lactose. Maximum polysaccharide concentration (11.0 ± 0.5 g L−1), biomass dry weight (10.5 ± 0.4 g L−1), polysaccharide yield (47.2 ± 1.8%) and sugar utilization (93.2 ± 2.8%) were achieved using enzyme-hydrolysed whey (pH 6.5)
containing 25 g L−1 lactose and supplemented with K2HPO4 0.5%, L-glutamic acid 1%, olive oil 2.5%, and Tween 80 0.5%. In this case the pullulan content of the crude polysaccharide was 40%.
Received 16 December 1997/ Accepted in revised form 12 March 1999 相似文献
20.
We have previously estimated the productivity and photosynthetic efficiency of the microalga Chlorella sp. grown in an outdoor open thin-layer photobioreactor under climate conditions typical of the Middle European region, i.e.
with many days unsuitable for intensive growth of algae (cloudy and rainy days, low air temperature, low solar PAR input).To
estimate the real potential productivity of the bioreactor, we collected data on algae yields obtained during clear summer
day periods. Cultivation was performed in fed-batch cycles in a bioreactor with a 224 m2 culture area (length 28 m, slope 1.7%), and a 6–7 mm-thick layer of algal culture. The suspension volume in the bioreactor
was 2,000 L. The mean values found for Třeboň (49°N), Czech Republic, as an average of several sunny summer cultivation periods
in July, were: net areal productivity, P
net = 38.2 g dry weight (DW) m-2 day-1; net volumetric productivity, Pvol, = 4.3 g algal DW L-1 day-1, photosynthetic efficiency (based on PAR), ηnet = 7.05%. The peak values were: P
net about 50 g (DW) m-2 day-1, ηnet about 9%. Algal growth rate was practically linear up to high biomass densities (40–50 g DW L-1, corresponding to an areal density of 240–300 g DW m-2), at which point the culture was harvested. The concentration of dissolved oxygen increased from about 10 mg L-1 at the beginning to about 23 mg L-1 at the end of culture area at noon. Use of the above-described technology for economical production of bioethanol is proposed. 相似文献