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1.
The diatom Eucampia zodiacus Ehrenberg is a harmful diatom which indirectly causes bleaching of aquacultured Nori (Porphyra thalli) through competitive utilization of nutrients during bloom events. In the present study, we experimentally investigated the nitrate (N) and phosphate (P) uptake kinetics of E. zodiacus, Harima-Nada strain. Maximum uptake rates (ρmax), which were obtained by short-term experiments, were 0.777 and 0.916 pmol cell?1 h?1 for nitrate and 0.244 and 0.550 pmol cell?1 h?1 for phosphate at 9 and 20 °C, respectively. The half-saturation constants for uptake (Ks) were 2.59 and 2.92 μM N and 1.83 and 4.85 μM P at 9 and 20 °C, respectively. Although the maximum specific uptake rate (Vmax; Vmax = ρmax/Q0, Q0; minimum cell quota) and Vmax/Ks for nitrate at 9 °C are about 1/2 of those obtained at the optimum temperature (20 °C), they are still higher than those obtained for many other phytoplankton at their optimum temperature conditions for uptake. These results suggest that E. zodiacus utilizes nitrogen efficiently at low water temperature, and it is one of the important factors causing the serious damage to Porphyra thalli by bleaching due of this species. For phosphate, the Ks values of E. zodiacus were higher than those reported for other species; the Vmax and Vmax/Ks values were much lower than those of other diatoms such as Skeletonema costatum (Greville) Cleve. These results suggest that E. zodiacus is disadvantaged compared to other diatom species during competitive utilization of phosphate.  相似文献   

2.
The uptake rates of different nitrogen (N) forms (NO3, urea, and the amino acids glycine and glutamic acid) by N-deficient, laboratory-grown cells of the mixotrophic haptophyte, Prymnesium parvum, were measured and the preference by the cells for the different forms determined. Cellular N uptake rates (ρcell, fmol N cell−1 h−1) were measured using 15N-labeled N substrates. P. parvum showed high preference for the tested amino acids, in particular glutamic acid, over urea and NO3 under the culture nutrient conditions. However, extrapolating these rates to Baltic Seawater summer conditions, P. parvum would be expected to show higher uptake rates of NO3 and the amino acids relative to urea because of the difference in average concentrations of these substrates. A high uptake rate of glutamic acid at low substrate concentrations suggests that this substrate is likely used through extracellular enzymes. Nitrate, urea and glycine, on the other hand, showed a non-saturating uptake over the tested substrate concentration (1–40 μM-N for NO3 and urea, 0.5–10 μM-N for glycine), indicating slower membrane-transport rates for these substrates.  相似文献   

3.
《Harmful algae》2011,10(6):531-539
Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO3), ammonium (NH4+), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using 15N tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO3 (Vmax 0.044 h−1; Ks 60.8 μM-N) was an important N source before it was depleted. NH4+ (Vmax 0.049 h−1; Ks 2.15 μM-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom (Vmax 0.020 h−1; Ks 1.35 μM-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom (Vmax 0.025 h−1; Ks 1.76 μM-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations.  相似文献   

4.
In the current work nanoparticles (NPs) of α-amylase were generated in an aqueous solution using high-intensity ultrasound, and were subsequently immobilized on polyethylene (PE) films, or polycarbonate (PC) plates, or on microscope glass slides. The α-amylase NPs coated on the solid surfaces have been characterized by ESEM, TEM, FTIR, XPS and AFM. The substrates immobilized with α-amylase were used for hydrolyzing soluble potato starch to maltose. The amount of enzyme introduced in the substrates, leaching properties, and the catalytic activity of the immobilized enzyme were compared. The catalytic activity of the amylase deposited on the three solid surfaces was compared to that of the same amount of free enzyme at different pHs and temperatures. α-Amylase coated on PE showed the best catalytic activity in all the examined parameters when compared to native amylase, especially at high temperatures. When immobilized on glass, α-amylase showed better activity than the native enzyme over all pH and temperature values studied. However, the immobilization on PC did not improve the enzyme activity at any pH and any temperature compared to the free amylase. The kinetic parameters, Km and Vmax were also calculated. The amylase coated PE showed the most favorable kinetic parameters (Km = 5 g L−1 and Vmax = 5E−07 mol mL−1 min−1). In contrast, the anchored enzyme-PC exhibited unfavorable kinetic parameters (Km = 16 g L−1, Vmax = 4.2E−07 mol mL−1 min−1). The corresponding values for amylase-glass were Km = 7 g L−1, Vmax = 1.8E−07 mol mL−1 min−1, relative to those obtained for the free enzyme (Km = 6.6 g L−1, Vmax = 3.3E−07 mol mL−1 min−1).  相似文献   

5.
β-Glucosidase catalyzes the sequential breakdown of cyanogenic glycosides in cyanogenic plants. The β-glucosidase from Prunus armeniaca L. was purified to 8-fold, and 20% yield was obtained, with a specific activity of 281 U/mg protein. The enzyme showed maximum activity in 0.15 M sodium citrate buffer, pH 6, at 35 °C with p-nitrophenylglucopyranoside as substrate. The β-glucosidase from wild apricot was used successfully for the saccharification of cellobiose into D-glucose. This enzyme has a Vmax of 131.6 μmol min−1 mg−1 protein, Km of 0.158 mM, Kcat of 144.8 s−1, Kcat/Km of 917.4 mM−1 s−1, and Km/Vmax of 0.0012 mM min mg μmole−1, using cellobiose as substrate. The half-life, deactivation rate coefficient, and activation energy of this β-glucosidase were 12.76 h, 1.509 × 10−5 s−1, and 37.55 kJ/mol, respectively. These results showed that P. armeniaca is a potential source of β-glucosidase, with high affinity and catalytic capability for the saccharification of cellulosic material.  相似文献   

6.
《Aquatic Botany》2002,72(3-4):219-233
We studied the potential role of dissolved inorganic carbon (DIC) in determining vegetation dominance of Potamogeton pectinatus L. and Chara aspera Deth. ex Willd. by monitoring the seasonal dynamics of DIC in a shallow lake and comparing the use of DIC of the two species. The HCO3-concentration in summer dropped from 2.5 to <0.5 mM with seasonally increasing Chara biomass, whereas outside the vegetation concentrations remained at 2.5 mM. Inside Potamogeton spp. vegetation DIC decreased from 2.5 to ca. 0.75 mM HCO3. A growth experiment showed ash-free biomass for P. pectinatus was nearly two times as high as for C. aspera at 3 mM HCO3, but almost two times lower at 0.5 mM than at 3.0. In a separate experiment, P. pectinatus precultured at a relatively low HCO3-level had a lower net photosynthetic rate (Pmax, 0.1 mmol O2 g−1 DW h−1) than C. aspera (Pmax, 0.1 mmol O2 g−1 DW h−1) over the range of HCO3-concentrations tested (Pmax, 0.14 mmol O2 g−1 DW h−1). In response to CO2 no significant differences between the compensation points (P. pectinatus, 28 mM; C. aspera 66 mM), were observed, but the photosynthetic rate increased faster than for C. aspera than for P. pectinatus. Under field conditions, the use of CO2 is not important since inside vegetation CO2-concentrations were below 10 μM, and thus, not available for photosynthesis of either species during the main part of the growth season. It is suggested that C. aspera may be a better competitor for HCO3 than P. pectinatus in conditions with a low HCO3 supply. As HCO3 is a strong limiting factor for growth inside the vegetation and probably the only carbon source available, the superior ability of C. aspera to use HCO3 may be an important factor explaining its present dominance in Veluwemeer.  相似文献   

7.
Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (Lmax) and the semi-optimum light intensity range (Ls-opt) that resulted in the maximum growth rate (μmax) and ≥80% μ max values of the four species/phylotypes, respectively, were as follows: (1) the Lmax and Ls-opt of G. australes were 208 μmol photons m−2 s−1 and 91–422 μmol photons m−2 s−1, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m−2 s−1, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m−2 s−1, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m−2 s−1, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m−2 s−1 to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m−1. The values 1700 μmol photons m−2 s−1, 500 μmol photons m−2 s−1, and 200 μmol photons m−2 s−1 were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of Lmax and Ls-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.  相似文献   

8.
We investigated the burst swimming performance of five species of Antarctic fish at −1.0°C. The species studied belonged to the suborder, Notothenioidei, and from the families, Nototheniidae and Bathydraconidae. Swimming performance of the fish was assessed over the initial 300 ms of a startle response using surgically attached miniature accelerometers. Escape responses in all fish consisted of a C-type fast start; consisting of an initial pronounced bending of the body into a C-shape, followed by one or more complete tail-beats and an un-powered glide. We found significant differences in the swimming performance of the five species of fish examined, with average maximum swimming velocities (Umax) ranging from 0.91 to 1.39 m s−1 and maximum accelerations (Amax) ranging from 10.6 to 15.6 m s−2. The cryopelagic species, Pagothenia borchgrevinki, produced the fastest escape response, reaching a Umax and Amax of 1.39 m s−1 and 15.6 m s−2, respectively. We also compared the body shapes of each fish species with their measures of maximum burst performance. The dragonfish, Gymnodraco acuticeps, from the family Bathdraconidae, did not conform to the pattern observed for the other four fish species belonging to the family Nototheniidae. However, we found a negative relationship between buoyancy of the fish species and burst swimming performance.  相似文献   

9.
The diatom Eucampia zodiacus is a harmful species that indirectly causes bleaching to nori (Pyropia) cultivation through competitive utilization of nutrients during its bloom, however cellular storage and changes in physiology by asexual reproduction remains unclear. In the present study, we experimentally investigated the nitrate (N), phosphate (P) and silicic acid (Si) consumption by various cell sizes of E. zodiacus strains, the apical axis length of which ranged from 10.2 to 77.3 μm. Nutrient cell quotas of E. zodiacus ranged from 2.7 to 8.4 pM cell−1 for N, 0.34–0.76 pM cell−1 for P and 1.7–7.3 pM cell−1 for Si, and they increased with cell size, in which there is a significant correlation between these two elements. The N and P quotas were estimated to be several times higher than the minimum cell quotas. In contrast, the Si cell quotas were approximately equal to those of the minimum values. Based on the present cell quotas, total nitrate consumption by E. zodiacus population when the blooms reached maximum cell density (=1000 cells ml−1) were estimated to be 6.5 μM. Monthly mean concentrations of dissolved inorganic nitrogen (DIN) range from 3.5 to 8.2 μM during the period of late nori harvest season when E. zodiacus blooms occur, and nori bleaching is reported at the condition of DIN concentration of less than 3 μM in Harima-Nada, eastern Seto Inland Sea, Japan. Therefore, the present results suggest that E. zodiacus causes serious damage to nori cultivation due to high levels of nutrient consumption.  相似文献   

10.
《Process Biochemistry》2014,49(10):1606-1611
The filamentous fungus Paecilomyces lilacinus was grown on n-hexadecane in submerged (SmC) and solid-state (SSC) cultures. The maximum CO2 production rate in SmC (Vmax = 11.7 mg CO2 Lg−1 day−1) was three times lower than in SSC (Vmax = 40.4 mg CO2 Lg−1 day−1). The P. lilacinus hydrophobin (PLHYD) yield from the SSC was 1.3 mg PLHYD g protein−1, but in SmC, this protein was not detected. The PLHYD showed a critical micelle concentration of 0.45 mg mL−1. In addition, the PLHYD modified the hydrophobicity of Teflon from 130.1 ± 2° to 47 ± 2°, forming porous structures with some filaments <1 μm and globular aggregates <0.25 μm diameter. The interfacial studies of this PLHYD could be the basis for the use of the protein to modify surfaces and to stabilize compounds in emulsions.  相似文献   

11.
《Process Biochemistry》2014,49(3):445-450
A cyanide hydratase from Aspergillus niger K10 was expressed in Escherichia coli and purified. Apart from HCN, it transformed some nitriles, preferentially 2-cyanopyridine and fumaronitrile. Vmax and Km for HCN were ca. 6.8 mmol min−1 mg−1 protein and 109 mM, respectively. Vmax for fumaronitrile and 2-cyanopyridine was two to three orders of magnitude lower than for HCN (ca. 18.8 and 10.3 μmol min−1 mg−1, respectively) but Km was also lower (ca. 14.7 and 3.7 mM, respectively). Both cyanide hydratase and nitrilase activities were abolished in truncated enzyme variants missing 18–34 C-terminal aa residues. The enzyme exhibited the highest activity at 45 °C and pH 8–9; it was unstable at over 35 °C and at below pH 5.5. The operational stability of the whole-cell catalyst was examined in continuous stirred membrane reactors with 70-mL working volume. The catalyst exhibited a half-life of 5.6 h at 28 °C. A reactor loaded with an excess of the catalyst was used to degrade 25 mM KCN. A conversion rate of over 80% was maintained for 3 days.  相似文献   

12.
《Aquatic Botany》2004,79(2):111-124
The main aim of this study was to investigate if the charophyte species Chara baltica, Chara canescens (two populations from the Baltic Sea (BS) and the Gulf of Korinth, Greece (GK)), and Lamprothamnium papulosum exhibit different acclimation capacities to irradiance. Growth, photosynthesis and pigment content were examined in the laboratory under six irradiance conditions (35–500 μmol photons m−2 s−1). Growth experiments showed increasing growth rates from 35 μmol photons m−2 s−1 (∼10 mg fresh weight (FW)) up to 70 μmol photons m−2 s−1 (∼20 mg FW) in C. baltica, from 35 μmol photons m−2 s−1 (∼15 mg FW) up to 380 μmol photons m−2 s−1 (∼145 mg FW) in C. canescens (BS), and up to the highest growth irradiance in algae of L. papulosum (35 μmol: ∼5 mg FW; 500 μmol: ∼20 mg FW). The species were tested for their ability to acclimate to different growth irradiances (Eg) by calculating Pmax (maximum photosynthesis rate at saturating irradiances), α (the efficiency of light utilization at limiting irradiance), and Ek (the light saturation point of photosynthesis, Pmax/α). All species exhibited increasing Pmax with increasing Eg. Whereas both populations of C. canescens increased α with increasing Eg, L. papulosum and C. baltica did not acclimate α at all. Ek, the irradiance at which photosynthesis ceased to be light-limited, was constant for all Chara species within the range of irradiances tested. Chl a/Chl b ratios of all species were constant over the whole range of Eg. Chl a/carotenoid ratios were constant in C. baltica, whereas Chl a/carotenoid ratios in L. papulosum and C. canescens (BS) decreased from 250 and 70 μmol photons m−2 s−1 upwards, respectively. Pigmentation analysis showed that Chl a/carotenoid acclimation was mainly caused by species-specific capacity to raise the content of lutein and carotene (C. canescens (BS), C. canescens (GK)) and xanthophyll cycle pigments (XCP; L. papulosum). The non-photochemical quenching (NPQ) capacities of L. papulosum, C. canescens (BS), and C. canescens (GK) were dependent from preacclimation status of algae, whereas NPQ of C. baltica was independent from growth irradiance.Our results indicate that C. baltica and C. canescens (BS) were light saturated within the chosen irradiances, whereas C. canescens (GK) and L. papulosum did not reach their limits of high-light acclimation. The photosynthetic pigments lutein, α- and β-carotene are suggested to act as photo-protective pigments in L. papulosum and C. canescens.  相似文献   

13.
Environmental factors that shape dynamics of benthic toxic blooms are largely unknown. In particular, for the toxic dinoflagellate Ostreopsis cf. ovata, the importance of the availability of nutrients and the contribution of the inorganic and organic pools to growth need to be quantified in marine coastal environments. The present study aimed at characterizing N-uptake of dissolved inorganic and organic sources by O. cf. ovata cells, using the 15N-labelling technique. Experiments were conducted taking into account potential interactions between nutrient uptake systems as well as variations with the diel cycle. Uptake abilities of O. cf. ovata were parameterized for ammonium (NH4+), nitrate (NO3) and N-urea, from the estimation of kinetic and inhibition parameters. In the range of 0 to 10 μmol N L−1, kinetic curves showed a clear preference pattern following the ranking NH4+ > NO3 > N-urea, where the preferential uptake of NH4+ relative to NO3 was accentuated by an inhibitory effect of NH4+ concentration on NO3 uptake capabilities. Conversely, under high nutrient concentrations, the preference for NH4+ relative to NO3 was largely reduced, probably because of the existence of a low-affinity high capacity inducible NO3 uptake system. Ability to take up nutrients in darkness could not be defined as a competitive advantage for O. cf. ovata. Species competitiveness can also be defined from nutrient uptake kinetic parameters. A strong affinity for NH4+ was observed for O. cf. ovata cells that may partly explain the success of this toxic species during the summer season in the Bay of Villefranche-sur-mer (France).  相似文献   

14.
《Aquatic Botany》2005,81(4):326-342
The effects of NH4+ or NO3 on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g−1 d−1), whereas the growth rate of Glyceria was 16% higher in NH4+-N cultures than in NO3-N cultures (mean = 66.7 and 57.4 mg g−1 d−1 of NH4+ and NO3 treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH4+ cultures than in NO3 cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH4+ treated plants by 16%. The tissue NH4+ concentration (mean = 1.6 μmol g fresh wt−1) was not affected by N treatment, whereas NO3 contents were higher in NO3 (mean = 1.5 μmol g fresh wt−1) than in NH4+ (mean = 0.4 μmol g fresh wt−1) treated plants. In Phragmites, NH4+ (mean = 1.6 μmol g fresh wt−1) and NO3 (mean = 0.2 μmol g fresh wt−1) contents were not affected by the N regime. Species did not differ in NH4+ (mean = 56.5 μmol g−1 root dry wt h−1) and NO3 (mean = 34.5 μmol g−1 root dry wt h−1) maximum uptake rates (Vmax), and Vmax for NH4+ uptake was not affected by N treatment. The uptake rate of NO3 was low in NH4+ treated plants, and an induction phase for NO3 was observed in NH4+ treated Phragmites but not in Glyceria. Phragmites had low Km (mean = 4.5 μM) and high affinity (10.3 l g−1 root dry wt h−1) for both ions compared to Glyceria (Km = 6.3 μM, affinity = 8.0 l g−1 root dry wt h−1). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH4+-N source may participates in the observed success of Glyceria at NH4+ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.  相似文献   

15.
The toxic HAB dinoflagellate Karenia brevis (Davis) G. Hansen & Ø. Moestrup (formerly Gymnodinium breve) exhibits a migratory pattern atypical of dinoflagellates: cells concentrate in a narrow (∼0–5 cm) band at the water surface during daylight hours due to phototactic and negative geotactic responses, then disperse downward at night via non-tactic, random swimming. The hypothesis that this daylight surface aggregation behavior significantly influences bacterial and algal productivity and nutrient cycling within blooms was tested during a large, high biomass (chlorophyll a >19 μg L−1) K. brevis bloom in October of 2001 by examining the effects of this surface layer aggregation on inorganic and organic nutrient concentrations, cellular nitrogen uptake, primary and bacterial productivity and the stable isotopic signature (δ15N, δ13C) of particulate material. During daylight hours, concentrations of K. brevis and chlorophyll a in the 0–5 cm surface layer were enhanced by 131% (±241%) and 32.1% (±86.1%) respectively compared with an integrated water sample collection over a 0–1 m depth. Inorganic (NH4, NO3+2, PO4, SiO4) and organic (DOP, DON) nutrient concentrations were also elevated within the surface layer as was both bacterial and primary productivity. Uptake of nitrogen (NH4+, NO3, urea, dissolved primary amines, glutamine and alanine) compounds by K. brevis was greatest in the surface layer for all compounds tested, with the greatest enhancement evident in urea uptake rates, from 0.08 × 10−5 ng N K. brevis cell−1 h−1 to 3.1 × 10−5 ng N K. brevis cell−1 h−1. These data suggests that this surface aggregation layer is not only an area of concentrated cells within K. brevis blooms, but also an area of increased biological activity and nutrient cycling, especially of nitrogen. Additionally, the classic dinoflagellate migration paradigm of a downward migration for access to elevated NO3 concentrations during the dark period may not apply to certain dinoflagellates such as K. brevis in oligotrophic nearshore areas with no significant nitricline. For these dinoflagellates, concentration within a narrow surface layer in blooms during daylight hours may enhance nutrient supply through biological cycling and photochemical nutrient regeneration.  相似文献   

16.
Cochlodinium polykrikoides is a globally distributed, ichthyotoxic, bloom-forming dinoflagellate. Blooms of C. polykrikoides manifest themselves as large (many km2) and distinct patches with cell densities exceeding 103 ml−1 while water adjacent to these patches can have low cell densities (<100 cells ml−1). While the effect of these blooms on fish and shellfish is well-known, their impacts on microbial communities and biogeochemical cycles are poorly understood. Here, we investigated plankton communities and the cycling of carbon, nitrogen, and B-vitamins within blooms of C. polykrikoides and compared them to areas in close proximity (<100 m) with low C. polykrikoides densities. Within blooms, C. polykrikoides represented more than 90% of microplankton (>20 μm) cells, and there were significantly more heterotrophic bacteria and picoeukaryotic phytoplankton but fewer Synechococcus. Terminal restriction fragment length polymorphism analysis of 16S and 18S rRNA genes revealed significant differences in community composition between bloom and non-bloom samples. Inside the bloom patches, concentrations of vitamin B12 were significantly lower while concentrations of dissolved oxygen were significantly higher. Carbon fixation and nitrogen uptake rates were up to ten times higher within C. polykrikoides bloom patches. Ammonium was a more important source of nitrogen, relative to nitrate and urea, for microplankton within bloom patches compared to non-bloom communities. While uptake rates of vitamin B1 were similar in bloom and non-bloom samples, vitamin B12 was taken up at rates five-fold higher (>100 pmol−1 L−1 d−1) in bloom samples, resulting in turn-over times of hours during blooms. This high vitamin demand likely led to the vitamin B12 limitation of C. polykrikoides observed during nutrient amendment experiments conducted with bloom water. Collectively, this study revealed that C. polykrikoides blooms fundamentally change microbial communities and accelerate the cycling of carbon, some nutrients, and vitamin B12.  相似文献   

17.
《Process Biochemistry》2010,45(1):88-93
A fibrinolytic protease (FP84) was purified from Streptomyces sp. CS684, with the aim of isolating economically viable enzyme from a microbial source. SDS-PAGE and fibrin zymography of the purified enzyme showed a single protein band of approximately 35 kDa. Maximal activity was at 45 °C and pH 7–8, and the enzyme was stable between pH 6 and 9 and below 40 °C. It exhibited fibrinolytic activity, which is stronger than that of plasmin. FP84 hydrolyzed Bβ-chains of fibrinogen, but did not cleave Aα- and γ-chains. Km, Vmax and Kcat values for azocasein were 4.2 mg ml−1, 305.8 μg min−1 mg−1 and 188.7 s−1, respectively. The activity was suppressed by Co2+, Zn2+, Cu2+ and Fe2+, but slightly enhanced by Ca2+ and Mg+2. Additionally, the activity was slightly inhibited by aprotinin and PMSF, but significantly inhibited by pefabloc, EDTA and EGTA. The first 15 amino acids of N-terminal sequence were GTQENPPSSGLDDID. They are highly similar to those of serine proteases from various Streptomyces strains, but different with known fibrinolytic enzymes. These results suggest that FP84 is a novel serine metalloprotease with potential application in thrombolytic therapy.  相似文献   

18.
Leifsonia xyli HS0904 can stereoselectively catalyze the bioreduction of 3,5-bis(trifluoromethyl) acetophenone (BTAP) to its corresponding alcohol, which is a valuable chiral intermediate in the pharmaceuticals. In this study, a new carbonyl reductase derived from L. xyli HS0904 was purified and its biochemical properties were determined in detail. The carbonyl reductase was purified by 530-fold with a specific activity of 13.2 U mg−1 and found to be a homodimer with a molecular mass of 49 kDa, in which the subunit molecular-weight was about 24 kDa. The purified enzyme exhibited a maximum enzyme activity at 34 °C and pH 7.2, and retained over 90% of its initial activity at 4 °C and pH 7.0 for 24 h. The addition of various additives, such as Ca2+, Mg2+, Mn2+, l-cysteine, l-glutathione, urea, PEG 1000 and PEG 4000, could enhance the enzyme activity. The maximal reaction rate (Vmax) and apparent Michaelis–Menten constant (Km) of the purified carbonyl reductase for BTAP and NADH were confirmed as 33.9 U mg−1, 0.383 mM and 69.9 U mg−1, 0.412 mM, respectively. Furthermore, this enzyme was found to have a broad spectrum of substrate specificity and can asymmetrically catalyze the reduction of a variety of ketones and keto esters.  相似文献   

19.
The vernal occurrence of toxic dinoflagellates in the Alexandrium tamarense/Alexandrium fundyense species complex in an enclosed embayment of Narragansett Bay (Wickford Cove, Rhode Island) was documented during 2005 and 2009–2012. This is the first report of regular appearance of the Alexandrium fundyense/Alexandrium tamarense species complex in Narragansett Bay. Thecal plate analysis of clonal isolates using SEM revealed cells morphologically consistent with both Alexandrium tamarense Lebour (Balech) and Alexandrium fundyense Balech. Additionally, molecular analyses confirmed that the partial sequences for 18S through the D1–D2 region of 28S were consistent with the identity of the two Alexandrium species. Toxin analyses revealed the presence of a suite of toxins (C1/2, B1 (GTX-5), STX, GTX-2/3. Neo, and GTX-1/4) in both Alexandrium tamarense (6.31 fmol cell−1 STX equiv.) and Alexandrium fundyense (9.56 fmol cell−1 STX equiv.) isolated from Wickford Cove; the toxicity of a Narragansett Bay Alexandrium peruvianum isolate (1.79 fmol cell−1 STX equiv.) was also determined. Combined Alexandrium tamarense/Alexandrium fundyense abundance in Wickford Cove reached a peak abundance of 1280 cells L−1 (May of 2010), with the combined abundance routinely exceeding levels leading to shellfishing closures in other systems. The toxic Alexandrium tamarense/Alexandrium fundyense species complex appears to be a regular component of the lower Narragansett Bay phytoplankton community, either newly emergent or previously overlooked by extant monitoring programs.  相似文献   

20.
Several parameters that influence the dibenzothiophene (DBT) desulfurization by lyophilized cells of Pseudomonas delafieldii R-8 were studied in the presence of dodecane. The aqueous media tested with pH range in 4.6–8.5 made no obvious difference on the desulfurization activity. The rate and extent of desulfurization were strongly dependent on the volume ratio of oil-to-water, DBT concentration and the cell concentration. The specific desulfurization rate of DBT and 4,6-dimethyl DBT (4,6-DMDBT) could reach 11.4 and 9.4 mmol sulfur kg−1 dry cells (DCW) h−1, respectively. The desulfurization pattern of DBT was represented by the Michaelis–Menten equation. The kinetic parameters, the limiting maximal velocity (Vmax) and Michaelis constant (Km), for desulfurization of DBT were calculated.  相似文献   

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