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101.
The profundal zone of Lake Esrom, Denmark has a dense population of Chironomus anthracinus, which survives 2–4 months of oxygen depletion each summer during stratification. The metabolism of 3rd and 4th instar larvae was examined in regard to variation in biomass and temperature. Respiration at air saturation was described by a curvilinear multiple regression relating oxygen consumption to individual AFDW and temperature. At 10 °C and varying oxygen regimes the O2 consumption and CO2 production of 4th instar larvae were almost unaltered from saturation to about 3 mg O2 l–1, but decreased steeply below this level. The respiratory quotient increased from 0.82 at saturation to about 3.4 at oxygen concentrations near 0.5 mg O2 l–1. This implied a shift from aerobic to partially anaerobic metabolism. At 0.5 mg O2 l–1 the total energy production equalled 20% of the rate at saturation of which more than one third was accounted for by anaerobic degradation of glycogen. This corresponded to a daily loss of 12 µg mg AFDW–1 or approximately 5% of the body reserves. At unchanged metabolic rate the glycogen store would last three weeks, but long term oxygen deficiency causes a further suppression of the energy metabolism in C. anthracinus. 相似文献
102.
High-density algal photobioreactors using light-emitting diodes 总被引:1,自引:0,他引:1
Lack of high-density algal photobioreactors (PBR) has been a limitation in exploiting the biotechnological potential of algae. Recent developments of highly efficient light-emitting diodes (LED using gallium aluminum arsenide chips) have made the development of a small LED-based PBR possible. We have calculated theoretical values of gas mass transfer requirements and light-intensity requirement to support high-density algal cultures for the 680 nm monochromatic red light from LED as a light source. A prototype PBR has been designed based on these calculations. A cell concentration of more than 2 x 10(9) cells/mL (more than 6.6% v%sol;v), cell doubling times as low as 12 h, and an oxygen production rate as high as 10 mmol oxygen/L culture/h were achieved using on-line ultrafiltration to periodically provide fresh medium. (c) 1994 John Wiley & Sons, Inc. 相似文献
103.
Metabolic shift analysis at high cell densities 总被引:2,自引:0,他引:2
M.J.Teixeira de Mattos J.P. de Boer G.R. Zoutberg O.M. Neijssel 《FEMS microbiology reviews》1994,14(1):21-28
Abstract: In high cell density cultures it is virtually inevitable that the environment to which the cells are exposed is heterogeneous. Thus, with suspended cultures, individual cells are subject to temporal changes in their environment whereas with aggregated or immobilized cells, the culture can be considered as being formed by a number of subpopulations, each with its own environmental characteristics. In addition, in a high cell density environment, high concentrations of end products may negatively influence the growth rate. This may result in the selection of organisms with an altered metabolic behaviour or with a decreased sensitivity to the adverse effects of the product. We discuss the consequences of this heterogeneity with regard to carbon source metabolism in view of the ability of many bacterial species to adapt to environmental conditions. Selection of variant organisms was found to occur with Clostridium butyricum when grown for a prolonged time in a medium containing approx. I-50 mM glucose. In contrast to the original strain, these variants could sustain a high maximal growth rate in the presence of butyric acid. In addition, they had acquired the capacity to spontaneously form aggregates and were able to carry out a completely solventogenic fermentation. Heterogeneous metabolic activity in aggregated cells is demonstrated with cultures of Lactobacillus laevolacticus , an aggregateforming lactic acid bacterium that converts glucose completely to o-lactate. By using microelectrodes, we show that the fraction of metabolically active cells decreases with increasing aggregate size: in larger aggregates steep pH gradients occur with the effect that only the outer layer of the aggregate is metabolically active, i.e. contributes to lactic acid formation, whereas with smaller aggregates all cells remain active. As a result, the net specific lactic acid production rate of the population as a whole is not invariably increased with increased aggregate size. 相似文献
104.
Michael W.W. Adams 《FEMS microbiology reviews》1994,15(2-3):261-277
Abstract: Hyperthermophiles are a recently discovered group of microorganisms that grow at and above 90°C. They currently comprise over 20 different genera, and except for two novel bacteria, all are classified as Archaea. The majority of these organisms are obligately anaerobic heterotrophs that reduce elemental sulfur (S°) to H2 S. The best studied from a biochemical perspective are the archaeon, Pyrococcus furiosus , and the bacterium, Thermotoga maritima , both of which are saccharolytic. P. furiosus is thought to contain a new type of Entner-Doudoroff pathway for the conversion of carbohydrates ultimately to acetate, H2 and CO2 . The pathway is independent of nicotinamide nucleotides and involves novel types of ferredoxin-linked oxidoreductases, one of which has tungsten, a rarely used element, as a prosthetic group. The only site of energy conservation is at the level of acetyl CoA, which in the presence of ADP and phosphate is converted to acetate and ATP in a single step. In contrast, T. maritima utilizes a conventional Embden-Meyerhof pathway for sugar oxidation. P. furiosus also utilizes peptides as a sole carbon and energy source. Amino acid oxidation is thought to involve glutamate dehydrogenase together with at least three types of novel ferredoxin-linked oxidoreductases which catalyze the oxidation of 2-ketoglutarate, aryl pyruvates and formaldehyde. One of these enzymes also utilizes tungsten. In P. furiosus , virtually all of the reductant that is generated during the catabolism of both carbohydrates and peptides is channeled to a cytoplasmic hydrogenase. This enzyme is now termed sulhydrogenase, as it reduces both protons to H2 and S°(or polysulfide) to H2 S. S° reduction appears to lead to the conservation of energy in P. furiosus but not in T. maritima , although the mechanism by which this occurs is not known. 相似文献
105.
D. M. Alongi 《Oecologia》1994,98(3-4):320-327
Benthic oxygen consumption and primary production were measured using the bell jar technique in deltaic and fringing mangrove forests of tropical northeastern Australia. In a deltaic forest, rates of sediment respiration ranged from 197 to 1645 mol O2 m–2 h–1 (mean=836), but did not vary significantly with season or intertidal zone. Gross primary production varied among intertidal zones and seasons, ranging from –281 to 1413 mol O2 m–2 h–1 (mean=258). Upon tidal exposure, rates of gross primary production increased, but respiration rates did not change significantly. In a fringing mangrove forest, benthic respiration and gross primary production exhibited strong seasonality. In both forests, rates of oxygen consumption and production were low compared to salt marshes, but equivalent to rates in other mangrove forests. The production:respiration (P/R) ratio varied greatly over space and time (range:–0.61 to 1.76), but most values were «1 with a mean of 0.15, indicating net heterotrophy. On a bare creek bank and a sandflat, rates of gross primary production and P/R ratios were generally higher than in the adjacent mangroves. Low microalgal standing stocks, low light intensity under the canopy, and differences in gross primary production between mangroves and tidal flats, and with tidal status, indicate that benthic microalgae are light-limited and a minor contributor to primary productivity in these tropical mangrove forests. 相似文献
106.
The duckweed Lemna gibba required light and a suitable energy source such as sucrose, glucose or fructose, for maximum growth in culture. The requirement
for light was relatively unimportant and the plants grew well in a photon flux density of only 52 μmol m-2s-1 PAR. The uptake and incorporation of uniformly labelled 14C-glucose into fronds was related only to the concentration of the sugar.
When incubated with soil, labelled L. gibba behaved in a manner similar to that of labelled ryegrass roots which had been produced by a more elaborate technique using
a 14CO2 labelled atmosphere. During incubation with soil for 224 days the L. gibba material (specific activity 6133 Bq mg-1 d. wt) lost 64% of its radioactivity as 14CO2 and ryegrass (specific activity 6634 Bq mg-1 d. wt) lost 49%. Alkaline extracted humic and fulvic acids from soil had specific activities for the L. gibba incubation of 3409 and 407 Bq mg-1 solid and for ryegrass roots of 4609 and 546 Bq mg-1 solid respectively. The production of 13C or 14C-labelled L. gibba can be undertaken using only simple equipment producing material the specific radioactivity of which can be controlled by
adjusting the activity of the sugar energy source. 相似文献
107.
Richard J. Robins Jack G. Woolley Morteza Ansarin John Eagles Brian J. Goodfellow 《Planta》1994,194(1):86-94
(S)-(-)-Tropic acid is the acidic moiety of the tropane ester alkaloids, hyoscyamine and scopolamine (hyoscine). When tropic acid is fed to transformed root cultures of Datura stramonium L. or a Brugmansia (Datura) Candida x B. aurea hybrid, the formation of these alkaloids is inhibited. Phenyllactic acid, from which the tropoyl moiety is derived, is considerably less inhibitory. Label from (RS)-phenyl[1,3-13C2]lactic acid is incorporated at high levels into apoatropine, littorine, aposcopolamine, hyoscyamine, 7-hydroxyapoatropine, scopolamine and 7-hydroxyhyoscyamine when fed to these cultures. The presence of an excess concentration of unlabelled tropic acid has little influence on the specific incorporation into these products. It is concluded that free tropic acid is not an intermediate in hyoscyamine biosynthesis but rather that the rearrangement of phenyllactic acid occurs subsequent to its esterification.Abbreviations FM
fresh mass
- NMR
nuclear magnetic resonance spectroscopy
We are grateful to Drs. N.J. Walton, A.J. Parr, M.J.C. Rhodes (Institue of Food Research, Norwich) and B. Dräger (Münster, Germany) for helpful and critical discussions. We also wish to thank Dr. P. Bachmann (Braunschweig, Germany) for suggesting the use of the DB-17 column to separate littorine from hyoscyamine and for the modified Excel programme used to calculate the specific incorporations, Yannick Ford (AFRC Co-operative Award Studentship, University of Oxford) and Abigael Peerless for their able assistance, Dr. I. Colquhoun for assistance with some of the NMR spectroscopy and Drs. K. Shimomura (Tsukuba, Japan) and T. Hashimoto (Kyoto, Japan) for pure samples of 7-hydroxyhyoscyamine. J.G.W, gratefully acknowledges support from the Nuffield Foundation under the Small Grants Scheme to promote collaborative experimentation and M.A. is grateful to the Ministry of Education, Iran for a research scholarship. 相似文献
108.
Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol−1 CO2 at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m−2 d−1). Elevated CO2 and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO2 enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO2 enrichment enhanced daily net CO2 uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol−1 CO2. Cladode chlorophyll content was lower in elevated CO2 and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO2 and at higher PPFD. The total plant nitrogen content was lower in elevated CO2. The effect of elevated CO2 on net CO2 uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO2 uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol−1 CO2. Averaged for the two CO2 treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD. 相似文献
109.
Ch. Sasikala Ch. V. Ramana G. S. Prasad 《World journal of microbiology & biotechnology》1994,10(2):221-223
Production of H2 from glucose by an anoxygenic phototrophic bacterium (Rhodobacter sphaeroides), a cyanobacterium (Synechococcus cedrorum) and a heterotrophic bacterium (Pseudomonas fluorescens) was tested individually and in mixed cultures of various combinations in light. H2 production was maximal with a mixed culture of R. sphaeroides and P. fluorescens, which could be further enhanced by immobilization of the bacteria in alginate gel. Inhibition of H2 photoproduction was observed in a mixture of S. cedrorum and P. fluorescens and a co-culture of all the three organisms.Ch. Sasikala and Ch. V. Ramana are and G. S. Prasad was with the Microbial Biotechnology Laboratory, Department of Botany, Osmania University, Hyderabad-500 007, India. G. S. Prasad is now with the Microbial Type Culture Collection Centre (MTCC), IMTECH, Chandigar, India. 相似文献
110.
Acetaldehyde production in Saccharomyces cerevisiae wine yeasts 总被引:1,自引:0,他引:1
Patrizia Romano Giovanna Suzzi Luca Turbanti Mario Polsinelli 《FEMS microbiology letters》1994,118(3):213-218
Abstract Eighty-six strains of Saccharomyces cerevisiae were investigated for their ability to produce acetaldehyde in synthetic medium and in grape must. Acetaldehyde production did not differ significantly between the two media, ranging from a few mg/l to about 60 mg/l, and was found to be a strain characteristic. The fermentation temperature of 30°C considerably increased the acetaldehyde produced. This study allowed us to assign the strains to different phenotypes: low, medium and high acetaldehyde producers. The low and high phenotypes differed considerably also in the production of acetic acid, acetoin and higher alcohols and can be useful for studying acetaldehyde production in S. cerevisiae , both from the technological and genetic point of view. 相似文献