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1.
Nitrate reduction by Citrobacter diversus under aerobic environment 总被引:17,自引:0,他引:17
A new aerobic denitrifier, Citrobacter diversus, was isolated from both nitrification and denitrification sludge. To monitor the variation in the concentration of nitrogen
oxides, aerobic denitrification by C. diversus was carried out in a batch reactor. When the nitrate concentration was greater than 180 mg N l−1, the nitrate reduction rate became stable. The effect of the C/N ratio on the denitrification activity was also investigated.
The results showed that the optimum denitrification activity was obtained when the C/N ratio was 4–5. The range of the C/N
ratio was higher than that for traditional anoxic denitrification. The effect of the dissolved oxygen concentration was further
studied; and it was found that the range of dissolved oxygen concentrations, both for specific growth rates and for specific
denitrification rates, was 2–6 mg−1. From these results, it can be concluded that both the concentration of dissolved oxygen and the C/N ratio are key factors
in the aerobic denitrification by C. diversus.
Received: 23 November 1999 / Received revision: 4 February 2000 / Accepted: 13 February 2000 相似文献
2.
P. Arvidsson K. Nilsson H. Håkanson B. Mattiasson 《Applied microbiology and biotechnology》1998,49(6):677-681
A chemiluminescence detector was used to measure the production of nitric oxide, NO, from the denitrifying bacteria Pseudomonas stutzeri. NO is an intermediate when P. stutzeri converts nitrate into nitrogen gas. The reaction between NO and ozone is selective and sensitive in generating chemiluminescence.
Calibrations were made down to 1 nM, with a signal-to-noise ratio of 3. Bacteria were immobilised in alginate beads. Denitrification
experiments were made in an anaerobic non-growth medium by adding nitrate to a certain concentration in the reactor. The bacteria
were exposed to nitrate in the concentration range 1 pM–5 mM. The lowest concentration to give a measurable NO response was
100 nM.
Received: 16 October 1997 / Received revision: 20 January 1998 / Accepted: 24 January 1998 相似文献
3.
During austral summer 1995 suprabenthic assemblages were investigated at 24 stations located around Livingston Island, Deception
Island and Bransfield Strait, at depths ranging from 45 to 650 m. Suprabenthos was collected on R/V Hesperides using a Macer-GIROQ sledge with an automatic opening and closing system. This study presents data on the occurrence and relative
abundance of the main suprabenthic groups collected in the water layer immediately adjacent to the bottom (10–140 cm above
bottom). Commonest groups were Amphipoda, Mysidacea, Isopoda, Cumacea and Euphausiacea. The distribution and spatial separation
in the suprabenthic habitat of the main groups are discussed.
Received: 20 February 1997 / Accepted: 14 July 1997 相似文献
4.
The continuous fermentation of 1,3-propanediol from glycerol by Clostridium butyricum was subjected to cell recycling by filtration using hollow-fibre modules made from polysulphone. The performance of the culture
system was checked at a retention ratio (dilution rate/bleed rate) of 5, dilution rates between 0.2 h−1 and 1.0 h−1 and glycerol input concentrations of 32 g l−1 and 56 g l−1. The near-to-optimum propanediol concentration of 26.5 g l−1 (for 56 g l−1 glycerol) was maintained up to a dilution rate of 0.5 h−1 and then decreased while the propanediol productivity was highest at 0.7 h−1. The productivity could be increased by a factor of four in comparison to the continuous culture without cell recycling.
By application of the model of Zeng and Deckwer [(1995) Biotechnol Prog 11: 71–79] for cultures under substrate excess, it
was shown that the limitations resulted exclusively from product inhibition and detrimental influences from the cell recycling
system, such as shear stress, were not involved.
Received: 20 October 1997 / Received revision: 12 December 1997 / Accepted: 14 December 1997 相似文献
5.
Effect of dissolved oxygen and carbon–nitrogen loads on denitrification by an aerobic consortium 总被引:10,自引:0,他引:10
Patureau D Bernet N Delgenès JP Moletta R 《Applied microbiology and biotechnology》2000,54(4):535-542
Four samples of natural ecosystems and one sample from an activated sludge treatment plant were mixed together and progressively
adapted to alternating aerobic/anoxic phases in the presence of nitrate in order to enrich the microflora in aerobic denitrifiers.
Aerobic denitrifying performances of this mixed ecosystem at various dissolved oxygen concentrations and various carbon–nitrogen
loads were evaluated and compared to those obtained with the aerobic denitrifier Microvirgula aerodenitrificans. The consortium and the pure strain exhibited an aerobic denitrifying activity at air saturation conditions (7 mg dissolved
oxygen l–1), i.e. there was co-respiration of the two electron acceptors with significant specific nitrate reduction rates. Dissolved
oxygen concentrations had no influence on denitrifying performances above a defined threshold: 0.35 mg l–1 for the consortium and 4.5 mg l–1 for M. aerodenitrificans respectively. Under these thresholds, decreasing the dissolved oxygen concentrations enhanced the denitrifying activity of
each culture. The higher the carbon and nitrogen loads, the higher the performance of the aerobic denitrifying ecosystem.
However, for M. aerodenitrificans, the nitrate reduction percentage was affected more by variations in nitrogen load than in carbon load.
Received: 6 December 1999 / Received revision: 8 March 2000 / Accepted: 10 March 2000 相似文献
6.
Toluene vapour removal in a laboratory-scale biofilter 总被引:4,自引:0,他引:4
A bench-scale biofilter with a 0.5-m high filter bed, inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, was used to study toluene removal from a synthetic waste air stream. Different sets of continuous tests were
conducted at influent toluene concentrations ranging over 0.1–4.0 g m−3 and at superficial gas velocities ranging over 17.8–255 m h−1. The maximum volumetric toluene removal rate for the biofilter (242 g m−3 h−1) was obtained at a superficial gas velocity of 127.5 m h−1 (corresponding to a residence time of 28 s) and a toluene inlet concentration of 4.0 g m−3. Under these operating conditions, toluene removal efficiency was only 0.238, which suggested that effective operation required
higher residence times. Removal efficiencies higher than 0.9 were achieved at organic loads less than 113.7 g m−3 h−1. A macro-kinetic study, performed using concentration profiles along the bioreactor, revealed this process was limited by
diffusion at organic loads less than 100 g m−3 h−1 and by biological reaction beyond this threshold.
Received: 10 October 1999 / Received revision: 15 February 2000 / Accepted: 18 February 2000 相似文献
7.
Optimization of agitation and aeration conditions for maximum virginiamycin production 总被引:3,自引:0,他引:3
To maximize the productivity of virginiamycin, which is a commercially important antibiotic as an animal feed additive, an
empirical approach was employed in the batch culture of Streptomyces virginiae. Here, the effects of dissolved oxygen (DO) concentration and agitation speed on the maximum cell concentration at the production
phase, as well as on the productivity of virginiamycin, were investigated. To maintain the DO concentration in the fermentor
at a certain level, either the agitation speed or the inlet oxygen concentration of the supply gas was manipulated. It was
found that increasing the agitation speed had a positive effect on the antibiotic productivity independent of the DO concentration.
The optimum DO concentration, agitation speed and addition of an autoregulator, virginiae butanolide C (VB-C), were determined
to maximize virginiamycin productivity. The optimal strategy was to start the cultivation at 450 rpm and to continue until
the DO concentration reached 80%. After reaching 80%, the DO concentration was maintained at this level by changing the agitation
speed, up to a maximum of 800 rpm. The addition of an optimal amount of the autoregulator VB-C in an experiment resulted in
the maximal production of virginiamycin M (399 mg/l), which was about 1.8-fold those obtained previously.
Received: 13 July 1998 / Received revision: 19 August 1998 / Accepted: 13 September 1998 相似文献
8.
A comparative study of the development of uptake hydrogenase and nitrogenase activities in cells of the cyanobacterium Anabaena variabilis was performed.
The induction of heterocysts is followed by the induction of both in vivo hydrogen uptake and nitrogenase activities. Interestingly,
a low but significant H2-uptake [2–7 μmoles of H2 · mg−1 (Chl a) · h−1] occurs in cultures with no heterocysts and with no nitrogenase activity. A slight stimulatory effect (30–40%) of H2 on in vivo H2-uptake was observed during the early stages of nitrogenase induction.
However, exogenous H2 does not further stimulate the induction of in vivo hydrogen uptake observed during heterocyst differentiation. Similarly,
organic carbon (fructose) did not influence the induction of either in vivo hydrogen uptake or nitrogenase activities. Exogenous
fructose supports higher in vivo hydrogen uptake and nitrogenase activities when the cells enter late exponential phase of
growth.
Received: 22 November 1995 / Accepted: 22 December 1995 相似文献
9.
A novel method for the determination of microbial growth kinetics on hydrophobic volatile organic compounds (VOC) has been
developed. A stirred tank reactor was operated as a fed-batch system to which the VOC was continuously fed via the gas phase,
assuring a constant VOC concentration in the mineral medium. A flow of air was saturated with the VOC, and then mixed with
a further flow of air, to obtain a predetermined VOC concentration. Thus, different VOC concentrations in the mineral medium
could be obtained by altering the VOC concentration in the feed gas. The growth kinetics of Xanthobacter autotrophicus GJ10 on 1,2-dichloroethane (DCE) and of Pseudomonas sp. strain JS150 on MonoChloroBenzene (MCB) were assessed using this method. The growth of strain JS150 was strongly inhibited
at MCB concentrations higher than 160 mg l−1, and the results were fitted using a piecewise function. The growth kinetics of strain GJ10 were described by the Luong model
where maximum growth rate μmax = 0.12 h−1, substrate saturation constant K
S = 7.8 mg l−1, and maximum substrate concentration S
m (above which growth is completely inhibited) = 1080 mg l−1. Varying nitrogen and oxygen flows enabled the effect of oxygen concentration on the growth kinetics of Pseudomonas JS150 to be determined.
Received: 30 November 1998 / Received revision: 19 March 1999 / Accepted: 20 March 1999 相似文献
10.
Jürgen Weissenberger 《Polar Biology》1998,19(3):151-159
A mesocosm experiment (enclosure volume 220 l) was designed such that sea ice inhabited by Arctic Sea ice organisms was formed
and maintained under natural conditions at 66°N in Rovaniemi, Finland. The experiment was run from natural freezing in December
1994 to melting in April 1995. The ice was inhabited by diatoms, chlorophyceae, heterotrophic flagellates, ciliates, nematodes
and turbellarians. Biomass in the ice, expressed as Chlorophyll a concentration, was 20–110 μg l−1; total cell densities varied from 5 × 106 to 35 × 106 cells l−1. Amongst phototrophic organisms, a succession from a flagellate-dominated community (Chlamydomonas sp.) to a multi-species diatom-dominated community was observed. Typical Arctic species such as Nitzschia frigida and Melosira arctica were present in the ice. Bacterial concentration varied between 2 × 108 and 7 × 108 cells l−1. At least two trophic levels were present in the ice.
Received: 3 April 1997 / Accepted: 9 September 1997 相似文献
11.
Andreas Erkens Klaus Schneider A. Müller 《Journal of biological inorganic chemistry》1996,1(2):99-110
In this study we confirmed the previous observation that the cytoplasmic NAD-linked hydrogenase of Alcaligenes eutrophus H16 is EPR-silent in the oxidized state. We also demonstrated the presence of significant Ni-EPR signals when the enzyme
was either reduced with the natural electron carrier NADH (5–10 mM) or carefully titrated with sodium dithionite to an intermediate,
narrow redox potential range (–280 to –350 mV). Reduction with NADH under argon atmosphere led to a complex EPR spectrum at
80 K with g values at 2.28, 2.20, 2.14, 2.10, 2.05, 2.01 and 2.00. This spectrum could be differentiated by special light/dark treatments
into three distinct signals: (1) the "classical" Ni-C signal with g values at 2.20, 2.14 and 2.01, observed with many hydrogenases in the reduced, active state; (2) the light-induced signal
(Ni-L) with g values at 2.28, 2.10 and 2.05 and (3) a flavin radical (FMN semiquinone) signal at g = 2.00. The assignment of the Ni-EPR signal was clearly confirmed by EPR spectra of hydrogenase labeled with 61Ni (nuclear spin I = 3/2) yielding a broadening of the Ni spectra at all g values and a resolved 61Ni hyperfine splitting into four lines of the low field edge in the case of the light-induced Ni-EPR signal. The redox potentials
determined at pH 7.0 for the described redox components were: for FMN –170 mV (midpoint potential, Em, for appearance), –200 mV (EPR signal intensity maximum) and –230 mV (Em for disappearance); for the Ni centre (Ni-C), –290 mV (Em for appearance), –305 mV (signal intensity maximum) and –325 mV (Em for disappearance). Exposure of the NADH-reduced hydrogenase to carbon monoxide led to an apparent Ni-CO species indicated
by a novel rhombic EPR signal with g values at 2.35, 2.08 and 2.01.
Received: 19 July 1995 / Accepted: 10 September 1995 相似文献
12.
The biochemical oxygen demand (BOD) test (BOD5) is a crucial environmental index for monitoring organic pollutants in waste water but is limited by the 5-day requirement
for completing the test. We have optimised a rapid microbial technique for measuring the BOD of a standard BOD5 substrate (150 mg glucose/l, 150 mg glutamic acid/l) by quantifying an equivalent biochemical mediator demand in the absence
of oxygen. Elevated concentrations of Escherichia coli were incubated with an excess of redox mediator, potassium hexacyanoferrate(III), and a known substrate for 1 h at 37 °C
without oxygen. The addition of substrate increased the respiratory activity of the microorganisms and the accumulation of
reduced mediator; the mediator was subsequently re-oxidised at a working electrode generating a current quantifiable by a
coulometric transducer. Catabolic conversion efficiencies exceeding 75% were observed for the oxidation of the standard substrate.
The inclusion of a mediator allowed a higher co-substrate concentration compared to oxygen and substantially reduced the incubation
time from 5 days to 1 h. The technique replicates the traditional BOD5 method, except that a mediator is substituted for oxygen, and we aim to apply the principle to measure the BOD of real waste
streams in future work.
Received: 2 August 1999 / Received revision: 6 December 1999 / Accepted: 12 December 1999 相似文献
13.
The transition rate kinetics from ethanol oxidation to glucose utilisation, within a structured model of baker’s yeast, described
previously, were experimentally identified. The shift in metabolism has been assessed through glucose pulses during batch
growth on ethanol. The influence of glucose concentration (between 0.25 g l-1 and 0.90 g l-1) and initial biomass concentration (between 0.61 g l-1 and 1.44 g l-1) on the transition rate was determined. The transition rate can not be described by a first-order saturation-type kinetics
with respect to glucose only. A corrective term, which takes into account biomass concentration should be included.
Received: 28 April 1995/Received revision: 6 July 1995/Accepted: 22 August 1995 相似文献
14.
15.
Local therapy with interleukin-2 (IL-2) and other cytokines may be a very effective way to treat cancer. This was the theme
of the First Symposium on Local Cytokine Therapy of Cancer: Interleukin-2, Interferons and Related Cytokines, in Hamburg,
29 April–1 May 1999. The abstracts are published in Anticancer Research 19: 1995–2016 (1999) [1]. Here we present a report.
Received: 28 October 1999 / Accepted: 2 December 1999 相似文献
16.
The effect of extracellular pH and dissolved oxygen on regulation of the pcbAB gene in P.␣chrysogenum was examined, using Northern analysis and a reporter gene fusion. It was found that ambient pH markedly affected levels of
pcbAB mRNA whereas maintenance of dissolved oxygen concentration above 10 % had no detectable effect. The presence of a DNA-binding
protein, which binds upstream of the pcbAB translational start codon, was also related to ambient pH. In all fermentations, pcbAB mRNA was most abundant at around the late exponential/early stationary phase of a culture.
Received: 10 May 1996 / Received revision: 14 October 1996 / Accepted: 25 October 1996 相似文献
17.
W. Sabra A. -P. Zeng S. Sabry S. Omar W. -D. Deckwer 《Applied microbiology and biotechnology》1999,52(6):773-780
Alginate production by Azotobacter vinelandii was studied in batch and continuous cultures under microaerobic conditions. In batch culture at a pO2 of 2–3% (air saturation) alginate production was enhanced by decreasing the PO3−
4 level in the medium. Alginate yield from biomass (Y
P/X) reached the highest value of 0.66 g/g at the lowest phosphate level (100 mg/l), compared to 0.40 g/g and 0.25 g/g at higher
phosphate levels (200 mg/l and 400 mg/l, respectively). In contrast, biomass formation behaved differently and the growth
yield (Y
X/S) decreased with decreasing PO4
3− concentrations. Moreover, the respiratory quotient (RQ) of the culture was dependent on the initial phosphate concentration,
especially in the phosphate-limited phase of growth. As the initial phosphate level decreased from 400 mg/l to 100 mg/l, the
average RQ value of the culture declined from 1.46 to 0.89. The low RQ value is very close to the theoretical optimum RQ,
calculated to be 0.8 on the basis of the stoichiometry of the metabolic pathways for alginate formation from sucrose. This
optimum RQ was also confirmed in continuous culture at different dilution rates. Independent of the dilution rate, a pO2 value of 2–5% (air saturation) was found to be optimal for alginate production, the corresponding RQ values being 0.80–0.84.
In addition, the molecular mass and composition of alginate were also found to be affected by both phosphate and oxygen concentrations.
In conclusion, the RQ appears to be a useful parameter for optimum control of alginate production with this microorganism.
Received: 31 March 1999 / Received revision: 2 July 1999 / Accepted: 5 July 1999 相似文献
18.
Plant cell suspension culture in a bench-scale fermenter with a newly designed membrane stirrer for bubble-free aeration 总被引:1,自引:0,他引:1
C. Böhme M.-B. Schröder H. Jung-Heiliger J. Lehmann 《Applied microbiology and biotechnology》1997,48(2):149-154
In this paper, tests of an optimized membrane-stirrer geometry for bubble-free aeration of a plant cell suspension culture
are described. Cell attachment and clogging of a previously described system [Piehl et al. (1988) Appl Microbiol Biotechnol
29:456–461] led to the development of a new stirrer. The volumetric oxygen transfer capacity has been measured in aqueous
medium. The mass transfer coefficient, k
l
a, was 3.75 h−1 at 25 °C and at a stirrer speed of 34 rpm. The overall oxygen transfer capacity was investigated with a suspension culture
of Aesculus hippocastanum. It was shown that the oxygen mass transfer was sufficient even at the maximum biomass of 10–12 g dry weight/l, which was
obtained by using this system. Furthermore, special attention was given to medium components like C and N sources, to avoid
growth limitation due to a shortage of nutrients.
Received: 22 October 1996 / Revised version: 11 March 1997 / Accepted: 14 March 1997 相似文献
19.
An efficient one-step transformation method for the dimorphic yeast Yarrowia lipolytica is described. Using cells grown overnight on agar plates, the whole process is carried out within 1 h. The transformant clones
could be recovered on selective plates as early as 36–48 h after plating. The efficiency was better than 105 transformants/μg replicative plasmid DNA. Effects of cell density, dithiothreitol, heat shock, poly(ethylene glycol) 4000
concentration and the wetness of selective plates were investigated.
Received: 17 February 1997 / Received revision: 4 April 1997 / Accepted: 19 April 1997 相似文献
20.
Removal of organic pollutants and of nitrate from wastewater from the dairy industry by denitrification 总被引:3,自引:0,他引:3
The aim of this work was to remove nitrate-N and organic pollutants from wastewater of the dairy industry by denitrification.
An artificially prepared wastewater, containing 250 mg/l nitrate-N and 1.5 g/l whey powder, was completely denitrified with
removal of 90%–93% of the chemical oxygen demand (COD) of the whey powder by suspended or immobilized mixed cultures and by
a suspended or immobilized pure culture that was isolated from the mixed culture inoculum. For the above COD/nitrate-N ratio
of 6:1, the results indicated that the organic compounds of the wastewater served as electron donors for complete denitrification
and that there was no need to add an external carbon source. In batch denitrification assays the suspended or immobilized
mixed cultures proved to be more active and reacted faster than the isolated pure cultures. In continuous denitrification
processes with immobilized pure or mixed cultures, the alginate beads, used for immobilization, were not stable for more than
12 days of incubation. The mixed free cultures removed the nitrate-N and COD continuously with no change of their activity
for at least 15 days at an optimum hydraulic retention time of 0.27 days with a loading rate of 900 mg nitrate-N l−1 day−1.
Received: 13 October 1997 / Received revision: 16 December 1997 / Accepted: 19 December 1997 相似文献