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1.
Influence of the Hydrological Cycle on the Bacterioplankton of an Impacted Clear Water Amazonian Lake 总被引:4,自引:0,他引:4
Abstract
Free-living and attached bacterial population sizes were determined fortnightly from December 1991 to December 1992 in natural
and disturbed areas of an Amazonian clear water lake (Batata Lake, Pará, Brazil) impacted by bauxite tailings. The bacterioplankton
showed distinct patterns during different phases of the hydrological cycle. Total bacterial population size and rates of thymidine
incorporation (measured during high and low water phases) were high during low water, with values ranging from 3.3 × 105 to 1.1 × 106 cells ml−1, and from 0.28 to 4.01 μg C l−1 h−1, respectively. The population size of free-living bacteria was larger at the natural station, while no differences were observed
between attached bacterial populations at both stations. However, production and turnover rate of attached bacteria were high
at the disturbed area. During low water, bacterial growth appeared to be driven mainly by the input of dissolved organic carbon
(DOC) from phytoplankton origin. During high water, bacterial abundance was reduced, probably as the result of dilution and
the input of less labile DOC from floodplains. The presence of bauxite tailings seems to influence bacterial dynamics in an
indirect way, probably due to shading of phytoplankton cells and, hence, reducing the DOC supply for bacterial growth. This
study, the first on the microbial ecology of an Amazonian clear water lake, demonstrated that water level variations exert
a strong influence on the bacterioplankton dynamics.
Received: 9 January 1996; Accepted 6 November 1996 相似文献
2.
An effective, simple, and convenient method to improve yeast’s multiple-stress tolerance, and ethanol production was developed.
After an ethanologenic Saccharomyces cerevisiae strain SC521 was treated by nine cycles of freeze-thaw, a mutant FT9-11 strain with higher multiple-stress tolerance was
isolated, whose viabilities under acetic acid, ethanol, freeze-thaw, H2O2, and heat-shock stresses were, respectively, 23-, 26-, 10- and 7-fold more than the parent strain at an initial value 2 × 107 c.f.u. per ml. Ethanol production of FT9-11 was similar (91.5 g ethanol l−1) to SC521 at 30°C with 200 g glucose l−1, and was better than the parent strain at 37°C (72.5 g ethanol l−1), with 300 (111 g ethanol l−1) or with 400 (85 g ethanol l−1) g glucose l−1. 相似文献
3.
The distributions of bacterial populations in sea ice and underlying seawater were investigated on the continental shelf of
the “Terre Adélie” area. A reference station was sampled weekly from January 1991 to January 1992. In winter, the survey included
a minimum of six sampling layers: surface and bottom ice, brine, seawater from the interface, and at 0.5 and 2 m depth. In
seawater, the total bacterial abundance ranged from 0.5 × 105 cells ml−1 in July to 6.0 × 105 cells ml−1 after ice break. Values reaching 2.5 × 106 cells ml−1 were recorded in the overlying ice cover. Mean cell volumes were twice as high in brine as in seawater. The saprophytic bacterial
abundance ranged from 5.0 × 104 CFU (colony-forming units) ml−1 in some winter interface samples to less than 1.0 × 103 CFU ml−1 in most of the summer seawater samples. In sea ice a clear decreasing gradient for most of the studied bacterial parameters
from the surface layers towards the bottom layer was found. The ice cover had a discernible impact on underlying seawater,
but its influence was restricted to a limited interface layer. 相似文献
4.
O. M. Tsivileva E. A. Loshchinina O. E. Makarov V. E. Nikitina 《Applied Biochemistry and Microbiology》2012,48(3):280-289
The auxin formation in a submerged culture of the xylotrophic basidiomycete Lentinus edodes (Berk.) Sing (Lentinula edodes (Berk.) Pegler) (shiitake) is studied. Biologically active substances of an indole nature are identified, “the effect of
small doses” of which lies in not only the stimulation of growth of the mycelium (indole-3-acetic acid, 2 × 10−7–2 × 10−4 g/l), but also in the induction of tryptophan-independent paths of auxin biosynthesis. The above-mentioned path is realized
in the presence of exogenous indole (1 × 10−3–1 × 10−4 g/l), as well as while inducing the biosynthesis of indole-3-acetic acid by its microadditives (1 × 10−5−1 × 10−8 g/l), and is accompanied by the formation of anthranilic acid (up to 1.5 mg/l). Induction of the generative development stage
of shiitake by indole derivatives is revealed. It was found that among the studied compounds only indoleacetamide at a concentration
of an order of ×10−4 g/l in the culture fluid of L. edodes had a pronounced stimulatory effect on the formation of shiitake’s brown mycelial film. 相似文献
5.
The bacteriostatic potency of the cerium-humic acid complex was evaluated by experimental measurement of this complex interaction
with E. coli, Bacillus pyocyaneus, Staphylococcus aureus, Leuconostoc and Streptococcus faecalis, and by comparison bacteriostatic effects with the cerium-citrate complex. The experimental results indicated that the cerium-humic
acid complex strongly inhibited growth of all five bacterial strains, and its diameter of bacteriostatic circles were more
than 30 mm. The minimal bacteria-inhibiting concentration were 1×10−3, 2×10−3 and 1×10−2 mol/L for E. coli and Bacillus pyocyaneus, Staphylococcus aureus, and Leuconostoc and Streptococcus faecalis individually, and the measured minimal bactericidal concentrations were 2×10−3 and 1×10−2 mol/L for Bacillus pyocyaneus, E. coli, and Leuconostoc. To kill Staphylococcus aureus and Streptococcus faecalis, the concentration had to be more than 1×10−2 mol/L. On the contrary, we found that cerium-citrate complex did not inhibit the growth of the above five bacteria, but stimulated
bacterial growth. The completely different bacteriostatic results of two cerium complexes may hint that the association and
chemical properties of the two complexes were different. 相似文献
6.
In previous experiments, rates of picoplankton uptake into coral communities were controlled by sponge and ascidian biomass.
Those experimental communities, however, had relatively few sponges and ascidians. In contrast, turbulent transport of particles
into the momentum boundary layers can limit particle removal by layered, dense bivalve populations. In this study, the role
of water velocity in controlling particulate nutrient-uptake by rubble communities was evaluated, in which the rubble was
more completely covered by sponges and ascidians. Picoplankton uptake was proportional to concentration over a range of cell
concentrations from 3.0 × 105 to 9.5 × 105 heterotrophic bacteria ml−1, 4.1 × 104 to 1.2 × 105
Synechococcus sp. ml−1 and 6.3 × 103 to 1.8 × 104 picoeukaryotes ml−1. The first-order uptake rate constants, normalized to sponge and ascidian biomass, were similar to previous experimental
communities. Picoplankton uptake increased 1.6-fold over a 7-fold change in water velocity, 0.05–0.35 m s−1. This increase has been interpreted as a result of higher turbulent transport within the rough coral community (canopy),
as indicated by a 1.6-fold increase in the bottom friction with increasing water velocity. 相似文献
7.
Measurements of total and culturable bacteria in the alfresco atmosphere using a wet-cyclone sampler 总被引:2,自引:0,他引:2
Alfresco (def. clean, outdoor) airborne bacteria were collected with a commercially available wet-cyclone bioaerosol sampler
to demonstrate its use, sample processing and resultant observations of total and culturable bacteria in mid-summer in the
mid-Willamette River Valley, OR. Some critiques of the system are given. The maximum and minimum total and culturable airborne
bacterial concentrations in the samples were 5.9 × 105 and 8.8 × 102 cells m−3, and 1.3 × 104 and 3.1 CFU m−3, respectively. What is thought to be a diurnal cycle was also observed for both fractions with highest concentrations during
the day and lowest at dawn and dusk. The culturable bacteria as a percentage of the total, was maximal at mid-day (≈ 3%) and
minimal at early morning and late evening (≈ 0.5–2%). Contrarily, the total bacteria in the downwind dust plume of a grass
seed combine was 2.9 × 106 cells m−3 and of these approximately 73% were culturable, a much greater culturable percentage than found in the alfresco outdoor atmosphere. 相似文献
8.
Tatiana G. Sazykina A. I. Kryshev K. D. Sanina 《Radiation and environmental biophysics》2009,48(4):391-404
Databases on effects of chronic low-LET radiation exposure were analyzed by non-parametric statistical methods, to estimate
the threshold dose rates above which radiation effects can be expected in vertebrate organisms. Data were grouped under three
umbrella endpoints: effects on morbidity, reproduction, and life shortening. The data sets were compiled on a simple ‘yes’
or ‘no’ basis. Each data set included dose rates at which effects were reported without further details about the size or
peculiarity of the effects. In total, the data sets include 84 values for endpoint “morbidity”, 77 values for reproduction,
and 41 values for life shortening. The dose rates in each set were ranked from low to higher values. The threshold TDR5 for
radiation effects of a given umbrella type was estimated as a dose rate below which only a small percentage (5%) of data reported
statistically significant radiation effects. The statistical treatment of the data sets was performed using non-parametric
order statistics, and the bootstrap method. The resulting thresholds estimated by the order statistics are for morbidity effects
8.1 × 10−4 Gy day−1 (2.0 × 10−4–1.0 × 10−3), reproduction effects 6.0 × 10−4 Gy day−1 (4.0 × 10−4–1.5 × 10−3), and life shortening 3.0 × 10−3 Gy day−1 (1.0 × 10−3–6.0 × 10−3), respectively. The bootstrap method gave slightly lower values: 2.1 × 10−4 Gy day−1 (1.4 × 10−4–3.2 × 10−4) (morbidity), 4.1 × 10−4 Gy day−1 (3.0 × 10−4–5.7 × 10−4) (reproduction), and 1.1 × 10−3 Gy day−1 (7.9 × 10−4–1.3 × 10−3) (life shortening), respectively. The generic threshold dose rate (based on all umbrella types of effects) was estimated
at 1.0 × 10−3 Gy day−1. 相似文献
9.
The use of clove oil as a potential anaesthetic for freshwater amphipods was examined at 20 °C. Individuals of Gammarus minus, a common species in southern Illinois, USA, spanning the entire body size range (4.3–14.3 mm), were used to test four anaesthetic
concentrations varying from 1.48 × 10−4 ml ml−1 to 5.9 × 10−4 ml ml−1. Small-bodied individuals (mean size = 5.4 mm ± 0.27SE) were used to test additional concentrations, up to 14.7 × 10−4 ml ml−1, a 10-fold span, to identify potential lethal concentrations. At the lowest concentration, time to anaesthesia and recovery
was constant at all body sizes. For the three next higher concentrations, time to anaesthesia decreased with increasing concentration
while recovery time increased. Activity of amphipods was not affected by the ethanol carrier. In addition, activity did not
differ between amphipods that had recovered from anaesthesia and unexposed amphipods. At clove oil concentrations of 8.84
× 10−4 ml ml−1 and 14.7 × 10−4 ml ml−1, mortality was 7 and 40%, respectively, indicating, that 5.9 × 10−4 ml ml−1 was a safe working concentration. No mortality was observed with Gammarus acherondytes, a federally endangered cave amphipod on which the protocol with 80 μl of stock was used in the field. The method enabled
us to obtain information on the endangered amphipod which normally would have required the sacrifice of individuals. Thus,
research can continue on species for which population numbers are low and for which basic information is needed to formulate
meaningful recovery plans. 相似文献
10.
Juan Fuentes F. B. Eddy 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(6):438-443
Drinking in Atlantic salmon (Salmo salar) juveniles was investigated in fresh water and following transfer to sea water. There was a significant effect of fish size
on drinking, and smolts (20–30 g) imbibed about ten times less water than alevins of 0.2–0.3 g. Freshwater smolts drank at
a rate of 0.15 ± 0.03 ml · kg−1 · h−1 and administration of doses of 10 or 20 mg · kg−1 of papaverine (stimulator of the renin- angiotensin system RAS) or [Asn1, Val5]-Angiotensin II (0.4 μmol · kg−1) resulted in significant increases in drinking, while administration of the angiotensin converting enzyme inhibitor, enalapril
(50 mg · kg−1) had no effect on drinking. Transfer of Atlantic salmon smolts to 1/3, 2/3 and full strength sea water resulted in significant
increases in drinking to 1.06 ± 0.12, 1.24 ± 0.0.16 and 3.89 ± 0.28 ml · kg−1 · h−1, respectively. In sea water, stimulation of the endogenous RAS by administration of papaverine (20 mg · kg−1) resulted in a 20% increase in drinking, while administration of enalapril to doses of 50 and 200 mg · kg−1 lowered drinking to 1.99 ± 0.48 and 0.32 ± 0.06 ml · kg−1 · h−1, respectively. All treatments were without effect on blood plasma levels of Na+ and Cl− in fresh water, while in sea water smolts both stimulation and inhibition of drinking resulted in hemoconcentration of Na+ and Cl−. The role of the renin angiotensin system in control of drinking and hydromineral balance in Atlantic salmon is discussed.
Accepted: 27 February 1997 相似文献
11.
Impact of soil vertical water movement on the energy balance of different land surfaces 总被引:4,自引:0,他引:4
The soil heat flux determination method proposed by Gao (Boundary-Layer Meteorol 114:165–178, 2005) is discussed for (1) dry
surfaces, (2) bare soil or sparse short-grass lands, and (3) dense-grass surfaces or forest. Our analysis shows that, when
neglecting the contribution of soil vertical water movement to soil heat flux, the energy components measured independently
will (1) still achieve balance over dry surfaces, and (2) be significantly in imbalance over bare soil or sparse short-grass
lands. The mean of bare ground evaporation modeled by SiB2 is 1.58 × 10−5 m3 s−1 m−2, and the mean of soil water flux obtained by the method of Gao is 1.22 × 10−5 m3 s−1 m−2 for the Naqu site in the summer of 1998. Comparison of the bare ground evaporation with the mean of soil water flux shows
a difference, the causes of which are investigated. Physically, the bare ground evaporation is equal to the sum of soil water
flux and water content change in the soil surface layer. Because the bare ground evaporation is very limited for the dense-grass
surfaces or forest, our analysis implies that the energy imbalance encountered over the dense-grass or forest is not caused
by the fact that previous researchers neglected soil water movements in their energy budget analyses. 相似文献
12.
Fred J. Genthner Janeshwar Upadhyay Robert P. Campbell Barbara R. Sharak Genthner 《Microbial ecology》1990,20(1):283-288
Culturable counts of antibiotic resistant, genetically engineeredPseudomonas fluorescens were determined on antibiotic-containing plate count agar during starvation in water. Prior to starvation, colony counts
obtained on all media separated into two groups. The mean of the colony counts on plate count agar with or without tetracycline
(4.9 × 106 ml−1) was significantly higher than the mean colony counts on plate count agar containing either nalidixic acid or nalidixic acid
plus tetraclycline (2.5×106 ml−1). After 20 days of starvation the highest mean colony counts continued to be obtained on plate count agar (7.2 × 106 ml−1) with slightly, but significantly, lower counts obtained on plate count agar containing either nalidixic acid (5.6 × 106 ml−1) or tetraclycline (1.5×106 ml−1). A combination of nalidixic acid and tetracycline in plate count agar, however, dramatically reduced colony counts (8.3
× 102 ml−1) after this starvation period. The addition of catalase to plate count agar containing nalidixic acid and tetracycline negated
the effect caused by this combination of antibiotics. When colony counts obtained over the entire 20 day incubation were considered,
the addition of MgSO4 to plate count agar containing nalidixic acid and tetracycline resulted in a significant increase in colony counts. Other
combinations of antibiotics, nalidixic acid+carbenicillin, nalidixic acid+kanamycin, streptomycin+tetracycline, streptomycin+carbenicillin,
rifampicin+tetracycline, rifampicin+carbenicillin, and rifampicin+kanamycin, did not inhibit colony formation of starved cells.
Antibiotic resistant strains ofP. putida andEscherichia coli also displayed sensitivity to the combination of nalidixic acid and tetracycline in plate count agar after starvation. 相似文献
13.
Li WB Gerstmann U Giussani A Oeh U Paretzke HG 《Radiation and environmental biophysics》2008,47(1):101-110
The mysterious death of Mr. Alexander Litvinenko who was most possibly poisoned by Polonium-210 (210Po) in November 2006 in London attracted the attention of the public to the kinetics, dosimetry and the risk of this high
radiotoxic isotope in the human body. In the present paper, the urinary excretion of seven persons who were possibly exposed
to traces of 210Po was monitored. The values measured in the GSF Radioanalytical Laboratory are in the range of natural background concentration.
To assess the effective dose received by those persons, the time-dependence of the organ equivalent dose and the effective
dose after acute ingestion and inhalation of 210Po were calculated using the biokinetic model for polonium (Po) recommended by the International Commission on Radiological
Protection (ICRP) and the one recently published by Leggett and Eckerman (L&E). The daily urinary excretion to effective dose
conversion factors for ingestion and inhalation were evaluated based on the ICRP and L&E models for members of the public.
The ingestion (inhalation) effective dose per unit intake integrated over one day is 1.7 × 10−8 (1.4 × 10−7) Sv Bq−1, 2.0 × 10−7 (9.6 × 10−7) Sv Bq−1 over 10 days, 5.2 × 10−7 (2.0 × 10−6) Sv Bq−1 over 30 days and 1.0 × 10−6 (3.0 × 10−6) Sv Bq−1 over 100 days. The daily urinary excretions after acute ingestion (inhalation) of 1 Bq of 210Po are 1.1 × 10−3 (1.0 × 10−4) on day 1, 2.0 × 10−3 (1.9 × 10−4) on day 10, 1.3 × 10−3 (1.7 × 10−4) on day 30 and 3.6 × 10−4 (8.3 × 10−5) Bq d−1 on day 100, respectively. The resulting committed effective doses range from 2.1 × 10−3 to 1.7 × 10−2 mSv by an assumption of ingestion and from 5.5 × 10−2 to 4.5 × 10−1 mSv by inhalation. For the case of Mr. Litvinenko, the mean organ absorbed dose as a function of time was calculated using
both the above stated models. The red bone marrow, the kidneys and the liver were considered as the critical organs. Assuming
a value of lethal absorbed dose of 5 Gy to the bone marrow, 6 Gy to the kidneys and 8 Gy to the liver, the amount of 210Po which Mr. Litvinenko might have ingested is therefore estimated to range from 27 to 1,408 MBq, i.e 0.2–8.5 μg, depending
on the modality of intake and on different assumptions about blood absorption. 相似文献
14.
Julio C. Davila Chandrasekara G. Reddy Patrick J. Davis Daniel Acosta 《In vitro cellular & developmental biology. Plant》1990,26(5):515-524
Summary The present study was undertaken to assess and compare the toxic effects of papaverine hydrochloride and its metabolites.
Primary cell cultures of rat hepatocytes were treated with papavarine (papaver), 3′-O-desmethyl (3′-OH), 4′-O-desmethyl (4′-OH),
and 6-O-desmethyl (6-OH) papaverine at 1×10−5, 1×10−4, and 1×10−3
M for 4,8, 12, and 24-h periods. Cell injury was determined by: a) cell viability using the trypan blue exclusion test; b)
cytosolic enzyme leakage of lactate dehydrogenase and aspartate aminotransferase; c) morphologic alterations; and d) lactate:
pyruvate (L:P) ratios. Cell cultures showed concentration-and time-dependent responses. For example, a decrease in cell viability
and an increase in enzyme leakage were observed after cell treatment with 1×10−4 and 1×10−3
M papaver for 8 h; 1×10−3
M 6-OH papaverine for 8 h and 1×10−4
M for 24 h; and 1×10−3
M 4′-OH papaverine for 24 h (P<0.05). Furthermore, changes in morphology correlated to cell viability and enzyme release in those cultures treated with
papaver, 4′-OH and 6-OH papaverine. Some of these changes included size deformation, cell detachment from the dishes, and
cell necrosis. On the other hand, an increase in L:P ratios (P<0.05) was detected with papaver as early as 8 h with 1×10−4 and 1×10−3
M and 12 h with 1×10−5
M; 6-OH showed an increase, in L:P ratios at 8 h with 1×10−3
M and 12 h with 1×10−4
M; these changes were evident with 4′-OH at 12 h with 1×10−3
M. In contrast, cells treated with 3′-OH papaverine did not show significant damage with any time period and concentration
used in this study. The results of this study indicate that papaverine-derived metabolites are less cytotoxic than its parent
compound, papaver. The toxicity was ranked as follows: papaver>6-OH>4′-OH>−3′-OH.
This work was supported in part by grant ES04200-02 from the National Institute of Environmental Health Sciences, Bethesda,
MD.
Presented in part at the fall ASPET meeting in Salt Lake City, August, 1989. Daniel Acosta is a Burroughs Wellcome Scholar
in Toxicology. 相似文献
15.
Viral abundance, burst sizes, lytic production and temperate phage were investigated in land-fast ice at two sites in Prydz
Bay Antarctica (68°S, 77°E) between April and November 2008. Both ice cores and brine were collected. There was no seasonal
pattern in viral or bacterial numbers. Across the two sites virus abundances ranged between 0.5 × 105 and 5.1 × 105 viruses ml−1 in melted ice cores and 0.6 × 105–3.5 × 105 viruses ml−1 in brine, and bacterial abundances between 2.7 × 104 and 17.3 × 104 cells ml−1 in melted ice cores and 3.9 × 104–32.5 × 104 cells ml−1 in brine. Virus to bacterium ratios (VBR) showed a clear seasonal pattern in ice cores with lowest values in winter (range
1.2–20.8), while VBRs in brine were lower (0.2–4.9). Lytic viral production range from undetectable to 2.0 × 104 viruses ml−1 h−1 in ice cores with maximum rates in September and November. In brine maximum, lytic viral production occurred in November
(1.18 × 104 viruses ml−1 h−1). Low burst sizes were typical (3.94–4.03 viruses per bacterium in ice cores and 3.16–4.0 viruses per bacterium in brine)
with unusually high levels of visibly infected cells—range 40–50%. This long-term investigation revealed that viral activity
was apparent within the sea ice throughout its annual cycle. The findings are discussed within the context of limited data
available on viruses in sea ice. 相似文献
16.
Water conductance of the cuticular membrane (CM) of mature sweet cherry fruit (Prunus avium L. cv. Sam) was investigated by monitoring water loss from segments of the outer pericarp excised from the cheek of the fruit.
Segments consisted of epidermis, hypodermis and several cell layers of the mesocarp. Segments were mounted in stainless-steel
diffusion cells with the mesocarp surface in contact with water, while the outer cuticular surface was exposed to dry silica
(22 ± 1 °C). Conductance was calculated by dividing the amount of water transpired per unit area and time by the difference
in water vapour concentration across the segment. Conductance values had a log normal distribution with a median of 1.15 × 10−4 m s−1 (n=357). Transpiration increased linearly with time. Conductance remained constant and was not affected by metabolic inhibitors
(1 mM NaN3 or 0.1 mM carbonylcyanide m-chlorophenylhydrazone) or thickness of segments (range 0.8–2.8 mm). Storing fruit (up to 42 d, 1 °C) used as a source of
segments had no consistent effect on conductance. Conductance of the CM increased from cheek (1.16 ± 0.10 × 10−4 m s−1) to ventral suture (1.32 ± 0.07 × 10−4 m s−1) and to stylar end (2.53 ± 0.17 × 10−4 m s−1). There was a positive relationship (r2=0.066**; n=108) between conductance and stomatal density. From this relationship the cuticular conductance of a hypothetical astomatous
CM was estimated to be 0.97 ± 0.09 × 10−4 m s−1. Removal of epicuticular wax by stripping with cellulose acetate or extracting epicuticular plus cuticular wax by dipping
in CHCl3/methanol increased conductance 3.6- and 48.6-fold, respectively. Water fluxes increased with increasing temperature (range
10–39 °C) and energies of activation, calculated for the temperature range from 10 to 30 °C, were 64.8 ± 5.8 and 22.2 ± 5.0 kJ
mol−1 for flux and vapour-concentration-based conductance, respectively.
Received: 23 March 2000 / Accepted: 28 July 2000 相似文献
17.
Lens Major Intrinsic Protein (MIP) is a member of a family of membrane transport proteins including the Aquaporins and bacterial
glycerol transporters. When expressed in Xenopus oocytes, MIP increased both glycerol permeability and the activity of glycerol kinase. Glycerol permeability (p
Gly
) was 2.3 ± 0.23 × 10−6 cm sec−1 with MIP vs. 0.92 ± 0.086 × 10−6 cm sec−1 in control oocytes. The p
Gly
of MIP was independent of concentration from 5 × 10−5 to 5 × 10−2
m, had a low temperature dependence, and was inhibited approximately 90%, 80% and 50% by 1.0 mm Hg++, 0.2 mm DIDS (diisothiocyanodisulfonic stilbene), and 0.1 mm Cu++, respectively. MIP-enhanced glycerol phosphorylation, resulting in increased incorporation of glycerol into lipids. This
could arise from an increase in the total activity of glycerol kinase, or from an increase in its affinity for glycerol. Based
on methods we present to distinguish these mechanisms, MIP increased the maximum rate of phosphorylation by glycerol kinase
(0.12 ± 0.03 vs. 0.06 ± 0.01 pmol min−1 cell−1) without changing the binding of glycerol to the kinase (K
M
∼ 10 μm).
Received: 23 May 1997/Revised: 4 August 1997 相似文献
18.
Uptake of glyeine,l-cysteine,l-leucine,l-methionine,l-aspartic acid andl-lysine was investigated in resting cells ofSaccharomyces cerevisiae treated with 0.3mm actidione for blocking protein synthesis. The amino acids were taken up against substantial concentration gradients (up to
nearly 1,000∶1 for μm l-cysteine and glycine). They were present in the free form inside the cells. Their unidirectional transmembrane fluxes were
under a negative feedback control by the intracellular concentration of the amino acid involved. The amino acids tested apparently
employed more than one transport agéncies for their membrane passage, the half-saturation constants being 6.2–7.7×10−4
m for glycine, 2.5×10−4
m forl-cysteine, 6×10−5 and 4×10−4
m forl-lysine, 3×10−5 and 6×10−4
m forl-methionine, 7–18×10−5 and 1.6×10−3
m forl-aspartic acid and 6×10−5 and 2×10−3
m forl-leucine. The specificities of the transport systems are overlapping but there emerges a wide-affinity transport system for
glycine, alanine, leucine, methionine, serine, cysteine, phenylalanine, aspartic acid, asparagine, glutamic acid and tryptophan
(and possibly for other amino acids), and more specific systems for each of the following: glycine, lysine, methionine, histidine,
arginine, and aspartic and glutamic acids. Proline had the peculiar effect of stimulating the transport of all the amino acids
tested. The amino acids apparently interacted in the uptake not only by competition for the binding site but also by allotopic
inhibition (e.g.l-cysteine) and possibly stimulation (l-proline). The initial rate of uptake of amino acids and their steady-state level of distribution were characterized by identical
activation energies: 7.5 kcal/mole forl-lysine, 6.9 kcal/mole forl-aspartic acid, and 13.2 kcal/mole for glycine. 相似文献
19.
Annual and interannual variability in phytoplankton at a permanent station off Kerguelen Islands, Southern Ocean 总被引:4,自引:4,他引:0
From November 1992 to February 1995 a quantitative and qualitative phytoplankton study was conducted at a permanent station
(Kerfix) southwest off the Kerguelen Islands, in the vicinity of the Polar Front (50°40′S–68°25′E). Phytoplankton populations
are low in this area both during summers and winters. They consist, in order of decreasing cell abundance, of pico- and nanoflagellates
(1.5–20 μm), coccolithophorids (<10 μm), diatoms (5–80 μm) and dinoflagellates (6–60 μm). Flagellates form the dominant group
throughout the year and attain the highest summer average of 3.0 × 105 cells l−1. Next in abundance year-round are coccolithophorids with the dominant Emiliania huxleyi (highest summer 1992 average 1.9 × 105 cells l−1), diatoms (summer 1992 average 1.0 × 105 cells l−1) and dinoflagellates (average 3.8 × 104 cells l−1). Winter mean numbers of flagellates and picoplankton do not exceed 8.4 × 104 cells l−1; those of the three remaining algal groups together attain 2 × 104 cells l−1. Summer peaks of diatoms and dinoflagellates are mainly due to the larger size species (>20 μm). The latter group contributes
most to the total cell carbon biomass throughout the year. Dominant diatoms during summer seasons include: Fragilariopsis kerguelensis, Thalassionema nitzschioides, Chaetoceros dichaeta, C. atlanticus, Pseudonitzschia heimii, and P. barkleyi/lineola. This diatom dominance structure changes from summer to summer with only F. kerguelensis and T. nitzschioides retaining their first and second positions. Any one of the co-dominant species might be absent during some summer period.
The variable diatom community structure may be due to southward meandering of the Polar Front bringing “warmer” species from
the north, and to the mixing of the water masses in this area. The entire community structure characterized both during summer
and winters by the dominance of flagellates can be related to deep mixing (ca. 40–200 m) of the water column as the probable
controlling factor.
Received: 13 November 1997 / Accepted: 11 May 1998 相似文献
20.
Abstract
Bacterial abundance and bacterivorous protist abundance and activity were examined in ice-brine and water column communities
of a cold temperate Japanese lagoon (Saroma-Ko Lagoon, Hokkaido, 44°N, 144°E), during the late winter phase of ice community
development (February–March 1992). Bacterial abundance averaged 6 and 1 × 105 cells ml−1 in the ice-brine and plankton samples, respectively, and generally decreased during the sampling period. Bacterivorous protists,
identified based on direct observation of short-term (<1 h) ingested fluorescently labeled bacteria (FLB) in their food vacuoles,
were largely dominated by flagellates, mainly cryothecomonad-type and chrysomonad-like cells and small dinoflagellates of
the genus Gymnodinium. Bacterivorous ciliates included mainly the prostomatid Urotricha sp., the scuticociliates Uronema and Cyclidium, the choreotrichs Lohmaniella oviformis and Strobilidium, and the hypotrich Euplotes sp. Protist abundance averaged 4 × 103 and 8.1 cells ml−1 in the ice-brine and 0.3 × 103 and 1.2 cells ml−1 in the plankton, for flagellates and ciliates, respectively. In contrast to bacteria, the abundance of protists generally
increased throughout the sampling period, indicating predator–prey interactions. Protistan bacterivory, measured from the
rate of FLB disappearance over 24 h, averaged 36% (ice) and 24% (plankton) of bacterial standing stock and exhibited the same
seasonal pattern as for protist abundance. The calculated specific clearance (range, 2–67 nl protozoa−1 h−1) and ingestion (<1–26 particles protozoa−1 h−1) rates were likely to be minimal estimates and grazing impact may have been higher on occasion. Indications for the dependence
of ``bacterivorous protists' on nonbacterial food items were also provided. Although alternative sources of bacterial loss
are likely to be of importance, this study provides evidence for the potential of protozoan assemblages as bacterial grazers
in both sea ice-brine biota and water column at the southern limit of sea ice in the northern hemisphere.
Received: 30 July 1998; Accepted: 18 November 1998 相似文献