The role of the gills in seawater adaptation inAnguilla dieffenbachii

Summary The mean serum sodium, chloride and potassium concentrations and serum osmotic pressure of freshwaterA. dieffenbachii are 140.4 mmol 1^–1,114.0 mmol 1^–1, 6.66 mmol 1^–1 and 307.7 mOsmol respectively. Gill tissue from freshwater specimens has a water content of 4234 mg g dry wt^–1 (80.9% wet wt), a chloride space of 1852 mg water g dry wt^–1 (35.2% wet wt) and an intracellular volume of 2449 mg water g dry wt (46.0% wet wt). Estimates of the intracellular sodium and potassium concentrations for the gill tissue of freshwater eels gave values of 28.9 mmol kg intracellular water^–1 and 126.5 mmol kg intracellular water^–1 respectively. On transfer of the fish to sea water serum concentrations of sodium and chloride and serum osmotic pressure show rapid initial increases followed by a more gradual decline eventually stabilising at new levels some 100 hours after transfer (Fig. 1). The serum sodium, chloride and potassium concentrations and serum osmotic pressure of seawater-adaptedA. dieffenbaehii are 162.8 mmol 1^–1, 151.0 mmol 1^–1, 6.70 mmol 1^–1 and 376.9 mOsmol respectively.On transfer to sea water the water content and chloride space of the gill tissue is reduced and the intracellular volume is initially decreased but is rapidly restored to its original value (Fig. 2, 3). At the same time intracellular sodium and potassium concentrations are increased but the latter is fairly rapidly restored to pre-transfer levels (Fig. 4).The changes in intracellular potassium concentration can be explained largely by the changes in intracellular volume but intracellular sodium concentrations remain high on transfer because of the increased serum sodium concentration. The initial increases in serum concentrations on transfer to sea water are caused partly by the removal of water and partly by the addition of sodium and chloride ions to the internal body fluids.     

Tissue osmolytes and body fluid compartments in the toad Bufo viridis under simulated terrestrial conditions

Summary Toads (Bufo viridis) were kept on soil without access to free water (simulated terrestrial conditions) for over 12 weeks. Body water compartments were estimated using the dilution method (inulin and Evans Blue). They were found to remain fairly constant after a period of adjustment which lasted 1–2 weeks. In particular, plasma volume was closely controlled. Plasma osmolarity increased to over 1000 mOsm · 1^–1 accompanying a large increase in its urea concentration. NaCl also increased, while potassium remained constant. Tissue (liver and skeletal muscle) water content did not change much and electrolytes were kept constant. Tissue water urea concentration seemed to equilibrate with that of the plasma. Urine osmolarity, which was hypotonic during water access, became nearly isosmotic and correlated with the plasma following transfer onto soil. Urine urea concentration correlated with the plasma in the terrestrial conditions, potassium was greatly elevated, sodium increased to some extent, and chloride hardly changed. The efficient osmoregulatory mechanisms for the control of distribution of body water sustain normal physiological functions.     

The Role of Glycerol and Inorganic Ions in Osmoregulatory Responses of the Euryhaline Flagellate Chlamydomonas pulsatilla Wollenweber

The green euryhaline flagellate Chlamydomonas pulsatilla Wollenweber, isolated from a coastal marine environment, was grown exponentially over the salinity range of 10 to 200% artificial seawater (ASW). The cellular volume and aqueous space of the alga, measured by [¹⁴C] mannitol and ³H₂O tracer analyses of centrifuged cell pellets, ranged between 2.3 and 3.1 picoliters and between 1.5 and 2.1 picoliters, respectively. The nonaqueous space determined in those analyses (28-35%) was consistent with the cell composition of the alga. The glycerol content of the alga increased almost linearly with increasing salinity; its contribution to intracellular osmolality at 200% ASW was about 57%. The contribution of amino acids and soluble carbohydrates to the cell osmotic balance was small. Intracellular ion concentrations determined by analyzing centrifuged cell pellets of known [¹⁴C]mannitol space by atomic absorption spectrophotometry, and by neutron activation analyses of washed cells were similar. At 10% ASW, potassium and magnesium were the major cations, and chloride and phosphate were the major anions. The sodium and chloride content of the alga increased with increasing salinity; at 200% ASW the intracellular concentration of both sodium and chloride was about 400 millimolar. The intracellular osmolality (π_int) matched closely the external osmolality (π_ext) over the entire salinity range except at 10% ASW where π_int exceeded π_ext by 120 to 270 milliosmoles per kilogram H₂O.     

Osmoregulation in Dunaliella tertiolecta: effects of salt stress,and the external pH on the internal pH

The intracellular pH of the halotolerant green algae Dunaliella tertiolecta, was determined by the distribution of 5,5-dimethyl-2(¹⁴C)-oxalolidine-2,5-dione (DMO) between the cell and the surrounding medium. 5,5-dimethyl-2(¹⁴C)oxalolidine-2,4-dione was not metabolized by the algal cells. The intracellular pH of Dunaliella tertiolecta was 6.8 in the dark and 7.4 in the light. During a salt stress, after two hours, the intracellular pH was increased by 0.2 pH units in both light and dark. The salt stressed cells maintained a constant pH of about 7.5 over the pH range of 6.5 to 8.5. Because of the relatively low permeability coefficient of the plasma membrane for DMO, this technique does not permit rapid pH determinations during the induction period after a salt stress. The magnitude of the salt induced pH changes measured 2 h after the salt stress implies a minor importance of this alkalization in this time range, but does not exclude a larger importance of pH changes for osmoregulation during the induction period.Abbreviations Chl chlorophyll - DMO 5,5-dimethyl-2(¹⁴C)oxalolidine-2,4-dione - PCV packed cell volume - SDS sodium dodecyl sulfate     

Influence of agitation and aeration on growth and antibiotic production by <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis>

The effect of agitation and aeration on the growth and antibiotic production by Xenorhabdus nematophila YL001 grown in batch cultures were investigated. Efficiency of aeration and agitation was evaluated through the oxygen mass transfer coefficient (K _L a). With increase in K _L a, the biomass and antibiotic activity increased. Activity units of antibiotic and dry cell weight were increased to 232 U ml⁻¹ and 19.58 g l⁻¹, respectively, productivity in cell and antibiotic was up more than 30% when K _L a increased from 115.9 h⁻¹ to 185.7 h⁻¹. During the exponential growth phase, DO concentration was zero, the oxygen supply was not sufficient. So, based on process analysis, a three-stage oxygen supply control strategy was used to improved the DO concentration above 30% by controlling the agitation speed and aeration rate. The dry cell weight and activity units of antibiotic were further increased to 24.22 g l⁻¹ and 249 U ml⁻¹, and were improved by 24.0% and 7.0%, compared with fermentation at a constant agitation speed and a constant aeration rate (300 rev min⁻¹, 2.5 l min⁻¹).     

Lymphocyte monovalent cation metabolism: cell volume, cation content and cation transport

Mechanisms which determine sodium and potassium content and volume of rat thymic and human chronic lymphocytic leukemia (CLL) lymphocytes have been studied. The deleterious effect of cell isolation on monovalent cation content was proven by comparing thymus sodium and potassium concentration to that of thymocytes prepared from autologous hemithymus. In vivo distribution ratios of sodium-24 and potassium-42 between thymus water and plasma water were very similar to the distribution ratios of non-radioactive isotopes (sodium-23 and potassium-39). The similar lymphocyte: thymocyte ratio of (a) cell volume (1.48), (b) cell sodium plus potassium (1.47) and (c) cell water (1.50) demonstrated the close correlation of lymphocyte volume with monovalent cation content and water content. Steady-state CLL lymphocyte sodium (32 ± 1.9 mM) and potassium (131 ± 5.1 mM) and thymocyte sodium (31 ± 1.2 mM) and potassium (136 ± 3.9 mM) were similar; however, these steady-state levels were maintained by quantitatively different membrane functions. Radiopotassium and radiosodium uptake by thymocytes was more rapid than by CLL lymphocytes. Ouabain-sensitive potassium influx was 2.4 times greater in thymic (8.70 ± 2.28 mmoles/cm²/min × 10^?8) than in CLL (3.24 ± 0.45 mmoles/cm²/min × 10^?8) lymphocytes. Potassium exodus was also slower in CLL lymphocytes as compared to thymocytes. Ouabain-sensitive sodium accumulation and ouabain-insensitive sodium accumulation were also slower in CLL lymphocytes than in rat thymocytes. Half-maximal ouabain inhibition of sodium entry was 7.5 × 10^?3 M in thymic and CLL lymphocytes. The inhibitory effect of ouabain on sodium and potassium transport was easily reversible. Oligomycin inhibited ouabain-sensitive potassium accumulation in both lymphocyte types. Four lines of evidence indicate the presence in the lymphocyte of a system of leaks and pumps, the latter subserved by a ouabain and oligomycin-sensitive (sodium-potassium) ATPase: (a) steady-state monovalent cation gradient (K ～ 20:1, Na ～ 5:1), (b) the inability to maintain normal sodium and potassium gradients at cold temperature and in the presence of ouabain, (c) the effect of ouabain and oligomycin on active potassium influx and (d) the restitution of steady-state sodium and potassium concentration after cell isolation, ouabain treatment and cold exposure. CLL lymphocytes as compared to rat thymocytes have a decreased rate of ouabain-insensitive sodium uptake and potassium exodus requiring a reduced rate of active sodium extrusion and potassium accumulation to maintain steady-state cation content. Ouabain-sensitive ATPase is difficult to locate in lymphocytes in vitro possibly because it comprises a very small proportion of membrane ATPase since magnesium activated ecto-ATPase in intact lymphocytes is 1500 to 2500 times that of the intact erythrocyte. The inhibition by ouabain of blast transformation, mitosis, amino acid accumulation and nucleic acid synthesis in vitro, may reflect the importance of ouabain-sensitive ATPase and monovalent cation transport in the function of lymphoid cells.     

Osmoregulation in the Extremely Euryhaline Marine Micro-Alga Chlorella autotrophica

Chlorella autotrophica (Clone 580) grows over the external salinity range of 1 to 400% artificial sea water (ASW), can photosynthesize over the range from 1 to 600% ASW, and survives the complete evaporation of seawater. The alga grown at high salinities shows an increase in cell volume and a small decrease in cell water content. Measurements of ion content were made by neutron activation analysis on cells washed in isoosmotic sorbitol solutions which contained a few millimolar of major ions to prevent ion leakage. Cells grown at various ASW concentrations contain large quantities of sodium, potassium, and chloride ions. Measurements of cations associated with cell wall and intracellular macromolecules were made to determine intracellular concentration of free ions. The proline content of cells increases in response to increases in external salinity. Cells in 300% ASW contain 1500 to 1600 millimolar proline.     

Effects of agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum

The effect of mechanical agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum was investigated in aerated continuous cultures with and without the added shear protectant Pluronic F68. Damage to cells was quantified through a decrease in the steady state concentration of the biomass in the photobioreactor. For a given aeration rate, the steady state biomass concentration rose with increasing rate of mechanical agitation until an upper limit on agitation speed was reached. This maximum tolerable agitation speed depended on the microalgal species. Further increase in agitation speed caused a decline in the steady state concentration of the biomass. An impeller tip speed of >1.56 m s^–1 damaged P. tricornutum in aerated culture. In contrast, the damage threshold tip speed for P. cruentum was between 2.45 and 2.89 m s^–1. Mechanical agitation was not the direct cause of cell damage. Damage occurred because of the rupture of small gas bubbles at the surface of the culture, but mechanical agitation was instrumental in generating the bubbles that ultimately damaged the cells. Pluronic F68 protected the cells against damage and increased the steady state concentration of the biomass relative to operation without the additive. The protective effect of Pluronic was concentration-dependent over the concentration range of 0.01–0.10% w/v.     

Sodium Exchange in Dog Ventricular Muscle : Relation to frequency of contraction and its possible role in the control of myocardial contractility

Sodium exchange was studied in the arterially perfused papillary muscle of the dog. Three kinetically defined phases accounted for all the myocardial sodium: phase 0 (vascular)-λ_o (exchange constant) = 3.6 min^-1 phase 1 (interstitial)-λ₁ = 0.62 min^-1; phase 2 (intracellular)-λ₂ < 0.020 min^-1 in quiescent muscles. The phase 2 exchange rate was proportional to frequency of contraction and increased by approximately 0.004 min^-1 for each 1 beat/min increment in rate in muscles demonstrating stable function. A sudden increase in frequency of contraction was followed by a marked increase in phase 2 sodium exchange if muscle function did not deteriorate. This increased exchange required 14 min to achieve a steady state. During this time active tension increased (positive staircase) and then declined to become stable as the sodium exchange stabilized. In muscles in which increased frequency of contraction produced a progressive decrease in active tension and contracture, sodium exchange failed to increase. The characteristics of sodium exchange are compared to those previously defined for calcium and potassium in the perfused dog papillary muscle. It is proposed that alteration in sodium exchange is a primary determinant of calcium and potassium movements and thereby plays a significant role in the control of myocardial contractility.     

The DNA,RNA and protein composition of the cyanobacterium Anacystis nidulans grown in light- and carbon dioxide-limited chemostats

The DNA, RNA and protein content of the cyanobacterium Anacystis nidulans was determined in light-limited and carbon dioxide-limited chemostat cultures over the dilution rate range, D=0.02 h^-1 to 0.19 h^-1. The macromolecular contents as a percentage of the dry weight and on a per cell basis varied significantly as a function of organism growth rate and the nature of the growth conditions. For both limitations the RNA content per cell increased [20–55 fg RNA (cell)^-1] with increasing dilution rate and also showed an increase as a percentage of the dry weight. The DNA content as a percentage of the dry weight showed a 2-fold decrease with increasing dilution rate over the range examined. On a per cell basis DNA reached a peak at D=0.1 h^-1 [4.5 fg DNA (cell)^-1] for light-limited organisms and at D=0.08 h^-1 [8.0 fg DNA (cell)^-1] for carbon dioxide-limited organisms. The q _RNA increased with increasing dilution rates over the complete growth rate range examined whilst q _DNA reached a maximum at D=0.09 to 0.10 h^-1. The protein content as a percentage of the dry weight was greater in CO₂-limited organisms than light-limited organisms but in both cultures declined as the dilution rate was increased above D=0.10 h^-1.     

Cell volume change of Escherichia coli under stringent control apparent increase of K in rel cells

With several pairs of rel⁺ and rel⁻ strains of Escherichia coli, the effects of amino acid starvation on the intracellular concentration of K⁺ and the rate of uptake of ⁴²K⁺ were investigated. In the early phase of the experiments, the intracellular concentration of K⁺ was estimated by the conventional method in which the cell volume per A₆₆₀ value of the culture was assumed to be constant, being not influenced by the variation of growth condition and strain. Apparently, the K⁺ concentration of rel⁺ cells was kept almost constant, while that of rel⁻ cells increased about 1.5-fold 2 h after the exposure to amino acid starvation. Unexpectedly, however, the above assumption was found not to be valid in the present study. The cell volume per A₆₆₀ changed only slightly in CP78 (rel⁺) cells, while it increased markedly in CP79 (rel⁻) cells after the exposure to amino acid starvation. Reestimation of the K⁺ concentrations based on the estimated respective values of cell volumes per A₆₆₀ revealed no significant difference between both strains. After all, the above apparent phenomenon was found to be due to the fact that the increase in cell volume of the rel⁺ cells was arrested upon amino acid starvation whereas that in the rel⁻ cells was not. The ⁴²K⁺ uptake by the rel⁺ cells was depressed upon amino acid starvation, whereas that by the rel⁻ cells increased. Some regulatory mechanism was suggested to operate in both strains to keep their K⁺ concentrations constant. When intracellular concentration of a metabolite is to be determined, importance of measurement of cell volume under the respective conditions, without assuming the constancy of the cell volume per A₆₆₀ of the culture, was pointed out.     

Enhanced welan gum production using a two-stage agitation speed control strategy in Alcaligenes sp. CGMCC2428

Batch fermentative production of welan gum by Alcaligenes sp. CGMCC2428 was investigated under various oxygen supply conditions using regulating agitation speed. Based on a three kinetic parameters analysis that includes specific cell growth rate (μ), specific glucose consumption rate (q _s), and specific welan formation rate (q _p), a two-stage agitation speed control strategy was proposed to achieve high concentration, high yield, and high viscosity of welan. During the first 22 h, the agitation speed in 7.5 L fermenter was controlled at 800 rpm to maintain high μ for cell growth. The agitation was then reduced step-wise to 600 rpm to maintain a changing profile with stable dissolved oxygen levels and obtain high qp for high welan accumulation. Finally, the maximum concentration of welan was reached at 26.3 ± 0.89 g L⁻¹ with a yield of 0.53 ± 0.003 g g⁻¹ and the welan gum viscosity of 3.05 ± 0.10 Pa s, which increased by an average of 15.4, 15.2, and 20.1% over the best results controlled by constant agitation speeds.     

Ion metabolism in a halophilic blue-green alga,Aphanothece halophytica

The intracellular ion content of the halophilic blue-green alga, Aphanothece halophytica was studied as a function of age, external sodium and external potassium concentration. Intracellular Na⁺ was found to be about 0.38 millimoles/g dry mass. Intracellular K⁺ concentrations were as high as 1 M and varied directly with external salinity. Intracellular Ca⁺⁺ and Mg⁺⁺ were in the range previously reported for fresh water blue-green algae despite their extremely high extracellular concentrations. Average cell size is consistent at room temperature with two exceptions. When the outside K⁺ is lower than 6.5 mM the cells tend to be smaller with less intracellular K⁺ and high Ca⁺⁺. In stationary phase cultures the cells are larger with high intracellular Mg⁺⁺ and low K⁺.     

Na-NMR Studies of the Intracellular Sodium Ion Concentration in the Halotolerant Alga Dunaliella salina

The Intracellular Na⁺ concentration in the halotolerant alga Dunaliella salina was measured in intact cells by ²³Na-NMR spectroscopy, utilizing the dysprosium tripolyphosphate complex as a sodium shift reagent, and was found to be 88 ± 28 millimolar. Intracellular sodium ion content and intracellular volume were the same, within the experimental error, in cells adapted to grow in media containing between 0.1 and 4.0 molar NaCl. These values assume extracellular and intracellular NMR visibilities of the ²³Na nuclei of 100 and 40%, respectively. The relaxation rate of intracellular sodium was enhanced with increasing salinity of the growth medium, in parallel to the intracellular osmosity due to the presence of glycerol, indicating that Na⁺ ions and glycerol are codistribbuted within the cell volume.     

Intracellular sodium activity and sodium transport inNecturus gallbladder epithelium

Summary Ion-sensitive glass microelectrodes, conventional microelectrodes and isotope flux measurements were employed inNecturus gallbladder epithelium to study intracellular sodium activity, [Na] _i , electrical parameters of epithelial cells, and properties of active sodium transport. Mean control values were: [Na] _i : 9.2 to 12.1mm; transepithelial potential difference, _ms : –1.5 mV (lumen negative); basolateral cell membrane potential, _es : –62 mV (cell interior negative); sodium conductance of the luminal cell membrane,g _Na: 12 mho cm^–2; active transcellular sodium flux, 88 to 101 pmol cm^–2 sec^–1 (estimated as instantaneous short-circuit current). Replacement of luminal Na by K led to a decrease of the intracellular sodium activity at a rate commensurate to the rate of active sodium extrusion across the basolateral cell membrane. Mucosal application of amphotericin B resulted in an increase of the luminal membrane conductance, a rise of intracellular sodium activity, and an increase of short-circuit current and unidirectional mucosa to serosa sodium flux. Conclusions: (i) sodium transport across the basolateral membrane can proceed against a steeper chemical potential difference at a higher rate than encountered under control conditions; (ii) the luminal Na-conductance is too low to accommodate sodium influx at the rate of active basolateral sodium extrusion, suggesting involvement of an electrically silent luminal transport mechanism; (iii) sodium entry across the luminal membrane is the rate-limiting step of transcellular sodium transport and active sodium extrusion across the basolateral cell membrane is not saturated under control conditions.     

Role of agitation conditions in nitrification

The objective of this study was to determine the role of agitation conditions in the oxidation of nitrite ions by Nitrobacter. Batch reaction kinetic experiments were conducted in baffled stirred tanks. The range of agitation conditions studied was 6200 ? 95700 ergs/cm³ sec. This power input corresponds to 3.2 ? 45.6 hp/ 1000 gal, or a “hem Scale” of 3 ? 9. After a lag phase, the reaction kinetics were found to be zero order with respect to nitrite over a concentration range of 590 to 10 mg/liter nitrite nitrogen (NO₂^?-N). The zero-order rate constants were found to significantly decrease with increasing impeller power input per volume of liquid (P / V).     

Changes in the Membrane Permeability of Frog's Sartorius Muscle Fibers in Ca-Free EDTA Solution

The changes in the membrane permeability to sodium, potassium, and chloride ions as well as the changes in the intracellular concentration of these ions were studied on frog sartorius muscles in Ca-free EDTA solution. It was found that the rate constants for potassium and chloride efflux became almost constant within 10 minutes in the absence of external calcium ions, that for potassium increasing to 1.5 to 2 times normal and that for chloride decreasing about one-half. The sodium influx in Ca-free EDTA solution, between 30 and 40 minutes, was about 4 times that in Ringer's solution. The intracellular sodium and potassium contents did not change appreciably but the intracellular chloride content had increased to about 4 times normal after 40 minutes. By applying the constant field theory to these results, it was concluded that (a) P_Cl did not change appreciably whereas P_K decreased to a level that, in the interval between 10 and 40 minutes, was about one-half normal, (b) P_Na increased until between 30 and 40 minutes it was about 8 times normal. The low value of the membrane potential between 30 and 40 minutes was explained in terms of the changes in the membrane permeability and the intracellular ion concentrations. The mechanism for membrane depolarization in this solution was briefly discussed.     

The effects of modified ringer's solutions on the membrane potentials of innervated and denervated frog sartorius muscle fibers

Comparison has been made between innervated and chronically denervated frog sartorius muscle fibers for resting potentials and a number of features of the action potential. Muscles were obtained from force-fed frogs maintained at room temperature for periods up to one year, and were studied with intracellular microelectrodes. Denervated muscles increased in sensitivity to acetylcholine by 100–400-fold. Studies were made in normal Ringer's solution, and in media in which concentrations of K⁺, Na⁺, Ca⁺⁺, and Cl? were altered. The only significant differences noted between the denervated and the innervated fibers were a reduction in the maximum rate of fall of the action potential (ca. 20%) and an increase in the fall time of the active membrane potential (ca. 25%). These differences were present in normal Ringer's solution and remained when the bathing medium was modified. The resting membrane potential of denervated and innervated muscles varied with log [K⁺]_o in exactly the same manner, and followed the theoretical relation proposed by Hodgkin (Proc. Roy. Soc., B, 148: 1–37, ′58), with the term representing the ratio of the sodium to potassium permeabilities assigned a value of 0.01. The results suggest that (a) the resting sodium and potassium permeabilities are reduced proportionately after denervation, since it is known that denervated frog muscle has a smaller potassium permeability, and (b) the mechanism controlling the increase in potassium conductance during the action potential is less available after denervation. Data indicate that the system controlling the sodium permeability is capable of activation to the same extent as in innervated muscles. Muslces which had been allowed to reinnervate did not show the differences presented by the denervated muscles. Innervated and denervated muscles did not show any significant changes in maximum rates of rise or fall of the action potential, nor of the active membrane potential amplitude over a 30 mV range of resting membrane potentials, indicating that the sodium and potassium permeability systems are fully available in frog muscle at membrane potentials larger than ?80 mV.     

Improvement of poly(γ-glutamic acid) biosynthesis and quantitative metabolic flux analysis of a two-stage strategy for agitation speed control in the culture of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> NX-2

In this study, the production of poly(γ-glutamic acid) by Bacillus subtilis NX-2 (PGA) at different agitation speeds was investigated. Based on the analysis of specific cell growth rate (μ) and specific PGA formation rate (q _p ), a two-stage strategy for agitation speed control was proposed. During the first 24 h, an agitation speed of 600 rpm was used to maintain a high μ for better cell growth, which then reduced to 400 rpm after 24 h to maintain a high q _p to enhance PGA production. Using this method, the maximum concentration of PGA reached 40.5 ± 0.91 g/L and the PGA productivity was 0.56 ± 0.012 g/L/h, which was 17.7 and 9.8% higher, respectively, than the best results obtained when a constant agitation speed was used. The flux distributions and the related enzymes of 2-oxoglutarate could be affected by this two-stage strategy for agitation speed. The activity of isocitrate dehydrogenase and glutamate dehydrogenase at the key node of 2-oxoglutarate increased, and more flux distribution was directed to glutamate. The flux distribution from extracellular to intracellular glutamate also increased and improved PGA production as the glutamate uptake rates increased using the agitation-shift control method.     

Carotenoid and fatty acid metabolism in light‐stressed Dunaliella salina

β‐Carotene is overproduced in the alga Dunaliella salina in response to high light intensities. We have studied the effects of a sudden light increase on carotenoid and fatty acid metabolism using a flat panel photobioreactor that was run in turbidostat mode to ensure a constant light regime throughout the experiments. Upon the shift to an increased light intensity, β‐carotene production commenced immediately. The first 4 h after induction were marked by constant intracellular levels of β‐carotene (2.2 g LCV^?1), which resulted from identical increases in the production rates of cell volume and β‐carotene. Following this initial phase, β‐carotene productivity continued to increase while the cell volume productivity dropped. As a result, the intracellular β‐carotene concentration increased reaching a maximum of 17 g LCV^?1 after 2 days of light stress. Approximately 1 day before that, the maximum β‐carotene productivity of 30 pg cell^?1 day^?1 (equivalent to 37 mg LRV^?1 day^?1) was obtained, which was about one order of magnitude larger than the average productivity reported for a commercial β‐carotene production facility, indicating a vast potential for improvement. Furthermore, by studying the light‐induced changes in both β‐carotene and fatty acid metabolism, it appeared that carotenoid overproduction was associated with oil globule formation and a decrease in the degree of fatty acid unsaturation. Our results indicate that cellular β‐carotene accumulation in D. salina correlates with accumulation of specific fatty acid species (C16:0 and C18:1) rather than with total fatty acid content. Biotechnol. Bioeng. 2010;106: 638–648. © 2010 Wiley Periodicals, Inc.