Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding N:P dynamics in Ulva lactuca (Chlorophyta)

Dissolved inorganic phosphorus (DIP ) is an essential macronutrient for maintaining metabolism and growth in autotrophs. Little is known about DIP uptake kinetics and internal P‐storage capacity in seaweeds, such as Ulva lactuca (Chlorophyta). Ulva lactuca is a promising candidate for biofiltration purposes and mass commercial cultivation. We exposed U. lactuca to a wide range of DIP concentrations (1–50 μmol · L^?1) and a nonlimiting concentration of dissolved inorganic nitrogen (DIN ; 5,000 μmol · L^?1) under fully controlled laboratory conditions in a “pulse‐and‐chase” assay over 10 d. Uptake kinetics were standardized per surface area of U. lactuca fronds. Two phases of responses to DIP ‐pulses were measured: (i) a surge uptake (V_S ) of 0.67 ± 0.10 μmol · cm^?2 · d^?1 and (ii) a steady state uptake (V_M ) of 0.07 ± 0.03 μmol · cm^?2 · d^?1. Mean internal storage capacity (ISC_P ) of 0.73 ± 0.13 μmol · cm^?2 was calculated for DIP . DIP uptake did not affect DIN uptake. Parameters of DIN uptake were also calculated: V_S  = 12.54 ± 1.90 μmol · cm^?2 · d^?1, V_M  = 2.26 ± 0.86 μmol · cm^?2 · d^?1, and ISC_N  = 22.90 ± 6.99 μmol · cm^?2. Combining ISC and V_M values of P and N, nutrient storage capacity of U. lactuca was estimated to be sufficient for ~10 d. Both P and N storage capacities were filled within 2 d when exposed to saturating nutrient concentrations, and uptake rates declined thereafter at 90% for DIP and at 80% for DIN . Our results contribute to understanding the ecological aspects of nutrient uptake kinetics in U. lactuca and quantitatively evaluating its potential for bioremediation and/or biomass production for food, feed, and energy.     

Effects of light and temperature on the growth of Takayama helix (Dinophyceae): mixotrophy as a survival strategy against photoinhibition

Takayama helix is a mixotrophic dinoflagellate that can feed on diverse algal prey. We explored the effects of light intensity and water temperature, two important physical factors, on its autotrophic and mixotrophic growth rates when fed on Alexandrium minutum CCMP1888. Both the autotrophic and mixotrophic growth rates and ingestion rates of T. helix on A. minutum were significantly affected by photon flux density. Positive growth rates of T. helix at 6–58 μmol photons · m^?2 · s^?1 were observed in both the autotrophic (maximum rate = 0.2 · d^?1) and mixotrophic modes (0.4 · d^?1). Of course, it did not grow both autotrophically and mixotrophically in complete darkness. At ≥247 μmol photons · m^?2 · s^?1, the autotrophic growth rates were negative (i.e., photoinhibition), but mixotrophy turned these negative rates to positive. Both autotrophic and mixotrophic growth and ingestion rates were significantly affected by water temperature. Under both autotrophic and mixotrophic conditions, it grew at 15–28°C, but not at ≤10 or 30°C. Therefore, both light intensity and temperature are critical factors affecting the survival and growth of T. helix.     

Nitrogen Utilization and Toxin Production by Two Diatoms of the Pseudo‐nitzschia pseudodelicatissima Complex: P. cuspidata and P. fryxelliana

The toxigenic diatom Pseudo‐nitzschia cuspidata, isolated from the U.S. Pacific Northwest, was examined in unialgal batch cultures to evaluate domoic acid (DA) toxicity and growth as a function of light, N substrate, and growth phase. Experiments conducted at saturating (120 μmol photons · m^?2 · s^?1) and subsaturating (40 μmol photons · m^?2 · s^?1) photosynthetic photon flux density (PPFD), demonstrate that P. cuspidata grows significantly faster at the higher PPFD on all three N substrates tested [nitrate (NO₃^?), ammonium (NH₄⁺), and urea], but neither cellular toxicity nor exponential growth rates were strongly associated with one N source over the other at high PPFD. However, at the lower PPFD, the exponential growth rates were approximately halved, and the cells were significantly more toxic regardless of N substrate. Urea supported significantly faster growth rates, and cellular toxicity varied as a function of N substrate with NO₃^?‐supported cells being significantly more toxic than both NH₄⁺‐ and urea‐supported cells at the low PPFD. Kinetic uptake parameters were determined for another member of the P. pseudodelicatissima complex, P. fryxelliana. After growth of these cells on NO₃^? they exhibited maximum specific uptake rates (V_max) of 22.7, 29.9, 8.98 × 10^?3 · h^?1, half‐saturation constants (K_s) of 1.34, 2.14, 0.28 μg‐at N · L^?1, and affinity values (α) of 17.0, 14.7, 32.5 × 10^?3 · h^?1/(μg‐at N · L^?1) for NO₃^?, NH₄⁺ and urea, respectively. These labo‐ratory results demonstrate the capability of P. cuspidata to grow and produce DA on both oxidized and reduced N substrates during both exponential and stationary growth phases, and the uptake kinetic results for the pseudo‐cryptic species, P. fryxelliana suggest that reduced N sources from coastal runoff could be important for maintenance of these small pennate diatoms in U.S. west coast blooms, especially during times of low ambient N concentrations.     

METABOLIC AND ECOLOGICAL CONSTRAINTS IMPOSED BY SIMILAR RATES OF AMMONIUM AND NITRATE UPTAKE PER UNIT SURFACE AREA AT LOW SUBSTRATE CONCENTRATIONS IN MARINE PHYTOPLANKTON AND MACROALGAE1

Marine phytoplankton and macroalgae acquire important resources, such as inorganic nitrogen, from the surrounding seawater by uptake across their entire surface area. Rates of ammonium and nitrate uptake per unit surface area were remarkably similar for both marine phytoplankton and macroalgae at low external concentrations. At an external concentration of 1 μM, the mean rate of nitrogen uptake was 10±2 nmol·cm^?2·h^?1 (n=36). There was a strong negative relationship between log surface area:volume (SA:V) quotient and log nitrogen content per cm² of surface (slope=?0.77), but a positive relationship between log SA:V and log maximum specific growth rate (μ_max; slope=0.46). There was a strong negative relationship between log SA:V and log measured rate of ammonium assimilation per cm² of surface, but the slope (?0.49) was steeper than that required to sustain μ_max (?0.31). Calculated rates of ammonium assimilation required to sustain growth rates measured in natural populations were similar for both marine phytoplankton and macroalgae with an overall mean of 6.2±1.4 nmol·cm^?2·h^?1 (n=15). These values were similar to maximum rates of ammonium assimilation in phytoplankton with high SA:V, but the values for algae with low SA:V were substantially less than the maximum rate of ammonium assimilation. This suggests that the growth rates of both marine phytoplankton and macroalgae in nature are often constrained by rates of uptake and assimilation of nutrients per cm² surface area.     

Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

Nutrient uptake and alkaline phosphatase (ec 3:1:3:1) activity of emiliania huxleyi (PRYMNESIOPHYCEAE) during growth under n and p limitation in continuous cultures

Emiliania huxleyi (strain L) expressed an exceptional P assimilation capability. Under P limitation, the minimum cell P content was 2.6 fmol P·cell^?1, and cell N remained constant at all growth rates at 100 fmol N·cell^?1. Both, calcification of cells and the induction of the phosphate uptake system were inversely correlated with growth rate. The highest (cellular P based) maximum phosphate uptake rate (V_max^P) was 1400 times (i.e. 8.9 h^?1) higher than the actual uptake rate. The affinity of the P‐uptake system (dV/dS) was 19.8 L·μmol^?1·h^?1 at μ = 0.14 d^?1. This is the highest value ever reported for a phytoplankton species. V_max and dV/dS for phosphate uptake were 48% and 15% lower in the dark than in the light at the lowest growth rates. The half‐saturation constant for growth was 1.1 nM. The coefficient for luxury phosphate uptake (Q_maxt/Q_min) was 31. Under P limitation, E. huxleyi expressed two different types of alkaline phosphatase (APase) enzyme kinetics. One type was synthesized constitutively and possessed a V_max and half‐saturation constant of 43 fmol MFP·cell^?1·h^?1 and 1.9 μM, respectively. The other, inducible type of APase expressed its highest activity at the lowest growth rates, with a V_max and half‐saturation constant of 190 fmol MFP·cell^?1·h^?1 and 12.2 μM, respectively. Both APase systems were located in a lipid membrane close to the cell wall. Under N‐limiting growth conditions, the minimum N quotum was 43 fmol N·cell^?1. The highest value for the cell N‐specific maximum nitrate uptake rate (V_max^N) was 0.075 h^?1; for the affinity of nitrate uptake, 0.37 L·μmol^?1·h^?1. The uptake rate of nitrate in the dark was 70% lower than in the light. N‐limited cells were smaller than P‐limited cells and contained 50% less organic and inorganic carbon. In comparison with other algae, E. huxleyi is a poor competitor for nitrate under N limitation. As a consequence of its high affinity for inorganic phosphate, and the presence of two different types of APase in terms of kinetics, E. huxleyi is expected to perform well in P‐controlled ecosystems.     

Effects of nutrients on growth of the red-tide dinoflagellate <Emphasis Type="Italic">Gyrodinium instriatum</Emphasis> Freudenthal et Lee and a possible link to blooms of this species

We investigated the impact of different nitrogen (N) and phosphorus (P) compounds and concentrations on the growth of Gyrodinium instriatum Freudenthal et Lee in laboratory experiments, and possible links to blooms of this species at Hakozaki Fishing Port, Fukuoka, Japan. G. instriatum utilized only inorganic N compounds as N sources for growth. In contrast, G. instriatum utilized many inorganic and organic phosphorus compounds. We used the Monod equation to describe the growth rate of G. instriatum in N- or P-limited batch cultures as a function of ambient nutrient concentrations. Kinetic growth parameters for maximum specific growth rate (μ_max) and half-saturation nutrient concentration (K _S) were 0.57 divisions d⁻¹ and 14.2 μmol l⁻¹, respectively, under N-limitation and 0.65 divisions d⁻¹ and 1.75 μmol l⁻¹, respectively, under P-limitation. Compared with these K _S values, all in situ average dissolved inorganic nitrogen (DIN) concentrations in Hakozaki Fishing Port were higher than K _S for N, but all in situ average dissolved inorganic phosphorus (DIP) concentrations were lower than K _S for P, whether a red tide occurred or not bloom. Moreover, average DIP concentration in April (a month critical to red-tide genesis) of 2004 (a non-red-tide year) was less than half those in 2002 and 2003 (red-tide years). Thus, differences in DIP concentrations may be an important factor controlling blooms of G. instriatum in Hakozaki Fishing Port.     

Δ53β hydroxysteroid dehydrogenase activity of the rat corpus luteum exhibits positive substrate-binding co-operativity: A continuous monitoring microdensitometric study with unfixed ovarian tissue sections

Δ⁵3β hydroxysteroid dehydrogenase activity transforms biologically inactive Δ⁵3β hydroxy steroids into the active Δ⁴3-keto products (e.g. pregnenolone to progesterone). Using a cytochemical procedure which allows for the continuous microdensitometric monitoring of an enzyme reaction as it proceeds and a well described cytochemical assay for Δ⁵3β HSD we have analysed the initial velocity rates (V_o) for dehydroepiandrosterone (DHEA) binding to this enzyme in regressing (i.e. 20α hydroxy steroid dehydrogenase positive) corpus luteum (CL) cells in unfixed tissue sections (5 μm) of the dioestrous and proestrous rat ovary. The results are mean ± S.E.M. The relationship between DHEA concentration (0 to 50 μM) and Δ⁵3β HSD activity in the dioestrous corpora lutea was sigmoidal and had an atypical 1/V_o versus 1/S plot, the x intercept being positive. Using a 1/V_o versus 1/S² plot the V_max was determined to be 1·0 ± 0·08 μmol min^?1 mg^?1 CL (n = 6). The Hill constant was 2·7 ± 0·02 (n = 6) suggesting a high degree of positive co-operativity for DHEA binding. The S concentration for half maximal activity was 17 ± 1 μmoles (n = 6). In the corpora lutea cells of the proestrous ovary, the V_max for DHEA transformation was unchanged (0·95 ± 0·04 μmol min^?1 mg^?1, n = 3) whilst the S_0·5 was significantly increased to 27 ± 0·1 (p < 0·01, n = 3). The Hill constant remained positive being 2·9 ± 0·2 (n = 3). NAD⁺ binding to 3β HSD in regressing corpora lutea of the proestrous ovary has been demonstrated previously to be hyperbolic and fit the classical Michaelis-Menten model.¹ Extending the analysis of NAD⁺ binding to the regressing corpus luteum of the dioestrous rat ovary revealed similar kinetic characteristics to that seen with the proestrous enzyme, the apparent V_max and K_m being 0·84 ± 0·04 μmol min^?1 mg^?1 CL (n = 3) and 27 ± 7 μmol 1^?1 (n = 3) respectively. The Hill constant was 1·1 ± 0·03 (n = 3), indicating no co-operativity of co-factor binding.     

Effect of culturing parameters on the vegetative growth of Haematococcus alpinus (strain lcr‐cc‐261f) and modeling of its growth kinetics

The present study investigated the effect of different culture conditions on the vegetative growth of a new species, Haematococcus alpinus (strain LCR‐CC‐261f) using airlift photobioreactors. The influence of culture medium, aeration rates, CO₂ concentration in air‐gas mixture, temperature, light intensities, and wavelengths were investigated to achieve sustainable high cell density cultures. Growth parameters were determined by fitting the data to a form of the logistic equation that included a lag phase. The shear‐sensitive vegetative cells favored lower aeration rates in the photobioreactors. MLA medium increased to 40 mM nitrate produced high density cultures. Temperatures between 12°C and 18°C, 3% (v/v) CO₂ concentration and a narrow photon flux density ranging between 37 and 48 μmol photons · m^?2 · s^?1 were best suited for growth. The wavelength of the light source also impacted growth and a high cell density of 9.6 × 10⁵ cells · mL^?1 was achieved using a mixture of red and blue compared to warm white, red, or blue LEDs.     

Insecticidal Activity of the Leaf Essential Oil of Peperomia borbonensis Miq. (Piperaceae) and Its Major Components against the Melon Fly Bactrocera cucurbitae (Diptera: Tephritidae)

The essential oil from the leaves of Peperomia borbonensis from Réunion Island was obtained by hydrodistillation and characterized using GC‐FID, GC/MS and NMR. The main components were myristicin (39.5%) and elemicin (26.6%). The essential oil (EO) of Peperomia borbonensis and its major compounds (myristicin and elemicin), pure or in a mixture, were evaluated for their insecticidal activity against Bactrocera cucurbitae (Diptera: Tephritidae) using a filter paper impregnated bioassay. The concentrations necessary to kill 50% (LC₅₀) and 90% (LC₉₀) of the flies in three hours were determined. The LC₅₀ value was 0.23 ± 0.009 mg/cm² and the LC₉₀ value was 0.34 ± 0.015 mg/cm² for the EO. The median lethal time (LT₅₀) was determined to compare the toxicity of EO and the major constituents. The EO was the most potent insecticide (LT₅₀ = 98 ± 2 min), followed by the mixture of myristicin and elemicin (1.4:1) (LT₅₀ = 127 ± 2 min) indicating that the efficiency of the EO is potentiated by minor compounds and emphasizing one of the major assets of EOs against pure molecules.     

Postprocessing microflora of commercial attieke (a fermented cassava product) produced in the south of Côte d'Ivoire

The distribution and presence of hygiene indicator and pathogenic micro‐organisms in 375 samples of attieke marketed in Côte d'Ivoire, and their roles in the food poisoning were evaluated. Microbiological analyses were carried out, which included the total viable bacteria, coliforms, Escherichia coli, Staphylococcus aureus, Salmonella, Bacillus spores, fungi and Clostridium perfringens. The results revealed that the viable bacteria counts ranged from 2·2 ± 1·2 × 10⁵ to 3·4 ± 1·4 × 10⁶ CFU g^?1, while the yeasts and the moulds counts ranged, respectively, from 2·4 ± 0·12 × 10⁴ to 9·8 ± 0·4 × 10⁵ CFU g^?1 and 1·3 ± 0·7 × 10¹ to 1·7 ± 0·7 × 10² CFU g^?1. Bacillus subtilis, Bacillus cereus, Staphylococcus aureus, Citrobacter freundi, Enterobacter amnigenus, Citrobacter youngae, Enterobacter aerogenes, Klebsiella pneumoniae, Serratia marcescens, Enterobacter agglomerans and Klebsiella oxytoca were the bacteria isolated, and Rhizopus spp., Mucor spp., Thamnidium spp., Fusarium spp., Moniliella spp. the fungi. Escherichia coli, Clostridium perfringens and Salmonella spp. were not found. The occurrence of some bacteria and fungi illustrate that attieke collected in Côte d'Ivoire markets may act as a reservoir of pathogenic micro‐organisms for human.

Significance and Impact of Study

This study demonstrates the great need to carry out microbiological tests frequently on attieke and even more the need to apply correct HACCP system during the production. Attieke is especially a well‐known product in West Africa; hence, it is extremely important to ensure an adequate microbiological quality to guarantee consumers health. Overall, the study highlighted the need for effective communication on microbiological food risks, proper instruction and supervision in food‐handling procedures, greater education on food safety risks.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Variability in iodine in temperate seaweeds and iodine accumulation kinetics of Fucus vesiculosus and Laminaria digitata (Phaeophyceae,Ochrophyta)

The biogeochemistry of iodine in temperate coastal ecosystems is largely mediated by macroalgae, which act as a major biological sink and source of iodine. Their capacity to accumulate, retain and release iodine has been associated with abiotic and biotic stressors, but quantitative information is limited. We evaluated the seasonal iodine retention capacity of eleven macroalgal species belonging to different systematic groups, collected from two sites in Ireland. Iodine accumulation and retention were then further quantified in Fucus vesiculosus and Laminaria digitata in relation to I^? concentrations in seawater and temperature. In general, iodine contents were ~10¹–10² μmol · (g dw)^?1 for Laminariales, 10⁰–10¹ μmol · (g dw)^?1 for Fucales, 10^?1–10⁰ μmol · (g dw)^?1 for Rhodophyta, and 10^?1 μmol · (g dw)^?1 for Chlorophyta. Typically, algal iodine contents were above average in winter and below average in summer. Iodine accumulation in F. vesiculosus and L. digitata depended on I^? availability and followed the Michaelis‐Menten kinetic. The ratio of maximum accumulation rate to half accumulation coefficient (ρ_max: K _t) was 2.4 times higher for F. vesiculosus than for L. digitata , suggesting that F. vesiculosus was more efficient in iodine accumulation. Both species exhibited a temperature‐dependent net loss of iodine, and only an exposure to sufficient external I^? concentrations compensated for this loss. This study revealed that both environmental (e.g., I^? in seawater, temperature) and organismal (e.g., the status of the iodine storage pool) variables determine retention and variability in iodine in temperate seaweeds.     

Characterization of an ethanol‐tolerant 1,4‐β‐xylosidase produced by Pichia membranifaciens

Aims: The purification and biochemical properties of the 1,4‐β‐xylosidase of an oenological yeast were investigated. Methods and Results: An ethanol‐tolerant 1,4‐β‐xylosidase was purified from cultures of a strain of Pichia membranifaciens grown on xylan at 28°C. The enzyme was purified by sequential chromatography on DEAE cellulose and Sephadex G‐100. The relative molecular mass of the enzyme was determined to be 50 kDa by SDS‐PAGE. The activity of 1,4‐β‐xylosidase was optimum at pH 6·0 and at 35°C. The activity had a K_m of 0·48 ± 0·06 mmol l^?1 and a V_max of 7·4 ± 0·1 μmol min^?1 mg^?1 protein for p‐nitrophenyl‐β‐d ‐xylopyranoside. Conclusions: The enzyme characteristics (pH and thermal stability, low inhibition rate by glucose and ethanol tolerance) make this enzyme a good candidate to be used in enzymatic production of xylose and improvement of hemicellulose saccharification for production of bioethanol. Significance and Impact of the Study: This study may be useful for assessing the ability of the 1,4‐β‐xylosidase from P. membranifaciens to be used in the bioethanol production process.     

Nitrogen fixation by the diazotroph Cylindrospermopsis raciborskii (Cyanophyceae)

Nitrogen fixation has been proposed as a mechanism that allows the diazotrophic cyanobacterium, Cylindrospermopsis raciborskii, to bloom in nitrogen‐limited freshwater systems. However, it is unclear whether dinitrogen fixation (N₂ fixation) can supplement available dissolved inorganic nitrogen (DIN) for growth, or only provides minimum nitrogen (N) for cell maintenance under DIN deplete conditions. Additionally, the rate at which cells can switch between DIN use and N₂ fixation is unknown. This study investigated N₂ fixation under a range of nitrate concentrations. Cultures were grown with pretreatments of nitrate replete (single dose 941 μmol  · L^?1) and N‐free conditions and then either received a single dose of 941 μmol  · L^?1 (N941), 118 μmol  · L^?1 (N118) or 0 N. Heterocysts appeared from days 3 to 5 when treatments of high were transferred to N free media (N941:N0), and from day 5 in N941 transferred to N118 treatments. Conversely, transferring cells from N0 to N941 resulted in heterocysts being discarded from day 3 and day 5 for N0:N118. Heterocyst appearance correlated with a detectable rate of N₂ fixation and up‐regulation of nifH gene expression, the discard of heterocysts occurred after sequential reduction of nifH expression and N₂ fixation. Nitrate uptake rates were not affected by pretreatment, suggesting no regulation or saturation of this uptake pathway. These data demonstrate that for C. raciborskii, N₂ fixation is regulated by the production or discard of heterocysts. In conclusion, this study has shown that N₂ fixation only provides enough N to support relatively low growth under N‐limited conditions, and does not supplement available nitrate to increase growth rates.     

MRP2 and the Transport Kinetics of Cysteine Conjugates of Inorganic Mercury

Human exposure to mercuric species occurs regularly throughout the world. Mercuric ions may accumulate in target cells and subsequently lead to cellular intoxication and death. Therefore, it is important to have a thorough understanding of how transportable species of mercury are handled by specific membrane transporters. The purpose of the current study was to characterize the transport kinetics of cysteine (Cys)-S-conjugates of inorganic mercury (Cys-S-Hg-S-Cys) at the site of the multidrug resistance-associated transporter 2 (MRP2). In order to estimate the maximum velocity (V _max) and Michaelis constant (K _m) for the uptake of Cys-S-Hg-S-Cys mediated by MRP2, in vitro studies were carried out using radioactive Cys-S-Hg-S-Cys (5 μM) and inside-out membrane vesicles made from Sf9 cells transfected with MRP2. The V _max was estimated to be 74.3 ± 10.1 nmol mg protein⁻¹ 30 s⁻¹ while the K _m was calculated to be 63.4 ± 27.3 μM. In addition, in vivo studies were utilized to measure the disposition of inorganic mercury (administered dose 0.5 μmol kg⁻¹ in 2 mL normal saline) over time in Wistar and TR¯ (Mrp2-deficient) rats. These studies measured the disposition of mercuric ions in the kidney, liver, and blood. In general, the data suggest that the initial uptake of mercuric conjugates into select target cells is rapid followed by a period of slower uptake and accumulation. Overall, the data indicate that MRP2 transports Cys-S-Hg-S-Cys in a manner that is similar to that of other MRP2 substrates.

     

Standard metabolism and growth dynamics of laboratory‐reared larvae of Sardina pilchardus

This study provides the first measurements of the standard respiration rate (R_S) and growth dynamics of European sardine Sardina pilchardus larvae reared in the laboratory. At 15° C, the relationship between R_S (µl O₂ individual^?1 h^?1) and larval dry mass (M_D, µg) was equal to: R_S = 0·0057(±0·0007, ± s.e.)·M_D^{0·8835(±0·0268)}, (8–11% M_D day^?1). Interindividual differences in R_S were not related to interindividual differences in growth rate or somatic (Fulton's condition factor) or biochemical‐based condition (RNA:DNA).     

Disruption of glpF gene encoding the glycerol facilitator improves 1,3-propanediol production from glucose via glycerol in Escherichia coli

Engineered Escherichia coli has recently been applied to produce 1,3-propanediol (1,3-PDO) from glucose. A metabolic intermediate in the production pathway, glycerol, is partially secreted into the extracellular of E. coli through a glycerol facilitator encoded by glpF, and this secretion consequently decreases 1,3-PDO production. Therefore, we aimed to determine whether disrupting the glpF gene would improve 1,3-PDO production in E. coli. The intracellular glycerol concentration in a glpF-disruptant was 7·5 times higher than in a non-disruptant. The glpF-disrupted and non-disrupted E. coli strains produced 0·26 and 0·09 g l⁻¹ of 1,3-PDO, respectively, from 1% glucose after 72 h of cultivation. The specific growth rate (μ) and the 1,3-PDO yield from glucose (Y_P/S) in the disruptant were higher than those in the non-disruptant (ΔglpF, μ = 0·08 ± 0·00 h⁻¹, Y_P/S = 0·06 mol mol-glucose⁻¹; BW25113, μ = 0·06 ± 0·00 h⁻¹, Y_P/S = 0·02 mol mol-glucose⁻¹). Disruption of the glpF gene decreased the production of the by-product, acetic acid. These results indicated that disruption of glpF increased the intracellular concentration of glycerol and consequently increased 1,3-PDO production in E. coli.     

Influences of salinity on the physiology and distribution of the Arctic coralline algae,Lithothamnion glaciale (Corallinales,Rhodophyta)

In Greenland, free‐living red coralline algae contribute to and dominate marine habitats along the coastline. Lithothamnion glaciale dominates coralline algae beds in many regions of the Arctic, but never in Godthåbsfjord, Greenland, where Clathromorphum sp. is dominant. To investigate environmental impacts on coralline algae distribution, calcification and primary productivity were measured in situ during summers of 2015 and 2016, and annual patterns of productivity in L. glaciale were monitored in laboratory‐based mesocosm experiments where temperature and salinity were manipulated to mimic high glacial melt. The results of field and cold‐room measurements indicate that both L. glaciale and Clathromorphum sp. had low calcification and photosynthetic rates during the Greenland summer (2015 and 2016), with maximum of 1.225 ± 0.17 or 0.002 ± 0.023 μmol CaCO ₃ · g^?1 · h^?1 and ?0.007 ±0.003 or ?0.004 ± 0.001 mg O₂ · L^?1 · h^?1 in each species respectively. Mesocosm experiments indicate L. glaciale is a seasonal responder; photosynthetic and calcification rates increase with annual light cycles. Furthermore, metabolic processes in L. glaciale were negatively influenced by low salinity; positive growth rates only occurred in marine treatments where individuals accumulated an average of 1.85 ± 1.73 mg · d^?1 of biomass through summer. These results indicate high freshwater input to the Godthåbsfjord region may drive the low abundance of L . glaciale , and could decrease species distribution as climate change increases freshwater input to the Arctic marine system via enhanced ice sheet runoff and glacier calving.     

Acclimation conditions modify physiological response of the diatom Thalassiosira pseudonana to elevated CO2 concentrations in a nitrate‐limited chemostat

Diatoms are responsible for a large proportion of global carbon fixation, with the possibility that they may fix more carbon under future levels of high CO₂. To determine how increased CO₂ concentrations impact the physiology of the diatom Thalassiosira pseudonana Hasle et Heimdal, nitrate‐limited chemostats were used to acclimate cells to a recent past (333 ± 6 μatm) and two projected future concentrations (476 ± 18 μatm, 816 ± 35 μatm) of CO₂. Samples were harvested under steady‐state growth conditions after either an abrupt (15–16 generations) or a longer acclimation process (33–57 generations) to increased CO₂ concentrations. The use of un‐bubbled chemostat cultures allowed us to calculate the uptake ratio of dissolved inorganic carbon relative to dissolved inorganic nitrogen (DIC:DIN), which was strongly correlated with fCO₂ in the shorter acclimations but not in the longer acclimations. Both CO₂ treatment and acclimation time significantly affected the DIC:DIN uptake ratio. Chlorophyll a per cell decreased under elevated CO₂ and the rates of photosynthesis and respiration decreased significantly under higher levels of CO₂. These results suggest that T. pseudonana shifts carbon and energy fluxes in response to high CO₂ and that acclimation time has a strong effect on the physiological response.