Photosynthesis and apparent affinity for dissolved inorganic carbon by cells and chloroplasts of Chlamydomonas reinhardtii grown at high and low CO2 concentrations

Chloroplasts with high rates of photosynthetic O₂ evolution (up to 120 mol O₂· (mg Chl)^-1·h^-1 compared with 130 mol O₂· (mg Chl)^-1·h^-1 of whole cells) were isolated from Chlamydomonas reinhardtii cells grown in high and low CO₂ concentrations using autolysine-digitonin treatment. At 25° C and pH=7.8, no O₂ uptake could be observed in the dark by high- and low-CO₂ adapted chloroplasts. Light saturation of photosynthetic net oxygen evolution was reached at 800 mol photons·m^-2·s^-1 for high- and low-CO₂ adapted chloroplasts, a value which was almost identical to that observed for whole cells. Dissolved inorganic carbon (DIC) saturation of photosynthesis was reached between 200–300 M for low-CO₂ adapted chloroplasts, whereas high-CO₂ adapted chloroplasts were not saturated even at 700 M DIC. The concentrations of DIC required to reach half-saturated rates of net O₂ evolution (K_m(DIC)) was 31.1 and 156 M DIC for low- and high-CO₂ adapted chloroplasts, respectively. These results demonstrate that the CO₂ concentration provided during growth influenced the photosynthetic characteristics at the whole cell as well as at the chloroplast level.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon - K_m(DIC) coneentration of dissolved inorganic carbon required for the rate of half maximal net O₂ evolution - PFR photon fluence rate - SPGM silicasol-PVP-gradient medium     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Vectorial electron transport in Degulfovibrio vulgaris (Marburg) growing on hydrogen plus sulfate as sole energy source

Desulfovibrio vulgaris (Marburg) was grown on hydrogen plus sulfate as sole energy source in a medium containing excess iron. The topography of electron transport components was investigated. The bacterium contained per mg cells (dry weight) 30U hydrogenase (1U=1 mol/min), 35 g desulfoviridin (= bisulfite reductase), 0.6 U adenosine phosphosulfate reductase, 30 mU thiosulfate reductase, 0.3 nmol cytochrome c ₃ (M _r=13,000), 0.04 nmol cytochrome b, 0.85 nmol menaquinone, and 0.4 nmol ferredoxin. Hydrogenase (>95%) and cytochrome c ₃ (82%) were localized on the periplasmic side and desulfoviridin (95%), adenosine phosphosulfate reductase (87%), thiosulfate reductase (74%), and ferredoxin (71%) on the cytoplasmic side of the cytoplasmic membrane; menaquinone and cytochrome b were exlusively found in the membrane fraction. The location of the oxidoreductases indicate that in D. vulgaris (Marburg) H₂ oxidation and sulfate reduction take place on opposite sides of the cytoplasmic membrane rather than on the same side, as has recently been proposed.     

Ion transport across leech integument

The dorsal skin of the leech Hirudo medicinalis was used for electrophysiological measurements performed in Ussing chambers. The leech skin is a tight epithelium (transepithelial resistance = 10.5±0.5 k· cm^-2) with an initial short-circuit current of 29.0±2.9 A·cm^-2. Removal of Na⁺ from the apical bath medium reduced short-circuit current about 55%. Ouabain (50mol·l^-1) added to the basolateral solution, depressed the short-circuit current completely. The Na⁺ current saturated at a concentration of 90 mmol Na⁺·l^-1 in the apical solution (K _M=11.2±1.8 mmol·l^-1). Amiloride (100 mol·l^-1) on the apical side inhibited ca. 40% of the Na⁺ current and indicated the presence of Na⁺ channels. The dependence of Na⁺ current on the amiloride concentration followed Michaclis-Menten kinetics (K _i=2.9±0.4 mol·l^-1). The amiloride analogue benzamil had a higher affinity to the Na⁺ channel (K _i=0.7±0.2 mol·l^-1). Thus, Na⁺ channels in leech integument are less sensitive to amiloride than channels known from vertebrate epithelia. With 20 mmol Na⁺·l^-1 in the mucosal solution the tissue showed an optimum amiloride-inhibitable current, and the amiloride-sensitive current under this condition was 86.8±2.3% of total short-circuit current. Higher Na⁺ concentrations lead to a decrease in amiloride-blockade short-circuit current. Sitmulation of the tissue with cyclic adenosine monophosphate (100 mol·l^-1) and isobutylmethylxanthine (1 mmol·l^-1) nearly doubled short-circuit current and increased amiloride-sensitive Na⁺ currents by 50%. By current fluctuation analysis we estimated single Na⁺ channel current (2.7±0.9 pA) and Na⁺ channel density (3.6±0.6 channels·m^-2) under control conditions. After cyclic adenosine monophosphate stimulation Na⁺ channel density increased to 5.4±1.1 channels·m^-2, whereas single Na⁺ channel current showed no significant change (1.9±0.2 pA). These data present a detailed investigation of an invertebrate epithelial Na⁺ channel, and show the similarities and differences to vertebrate Na⁺ channels. Whereas the channel properties are different from the classical vertebrate Na⁺ channel, the regulation by cyclic adenosine monophosphate seems similar. Stimulation of Na⁺ uptake by cyclic adenosine monophosphate is mediated by an increasing number of Na⁺ channels.Abbreviations slope of the background noise component - ADH antidiuretic hormone - cAMP cyclic adenosine monophosphate - f frequency - f _c coner frequency of the Lorentzian noise component - Hepes N-hydroxyethylpiperazine-N-ethanesulphonic acid - BMX isobutyl-methylxanthine - i _Na single Na⁺ channel current - I _Na max, maximal inhibitable Na⁺ current - I _SC short circuit current - K _i half maximal blocker concentration - K _M Michaelis constandard error of the mean - S _(f) power density of the Lorentzian noise component - S ₀ plateau value of the Lorentzian noise component - TMA tetramethylammonium - Trizma TRIS-hydroxymethyl-amino-methane - V _max maximal reaction velocity - V _T transepithelial potential - K half maximal blocker concentration     

Growth,photosynthesis and photorespiration of Lemna gibba: response to variations in CO2 and O2 concentrations and photon flux density

Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO₂ enrichment up to 6000 l CO₂ l^–1. This high CO₂ optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO₂ was less or absent following four days growth in 2% O₂. The Leaf Area Ratio decreased in response to CO₂ enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO₂ enrichment up to 1500 l CO₂ l^–1 during measurement, showing only small increases with further CO₂ enrichment up to 5000 l CO₂ l^–1 at a photon flux density of 210 mol m^–2 s^–1 and small decreases at 2000 mol m^–1 s^–1. The actual rate of photosynthesis of those plants cultivated at high CO₂ levels, however, was less than the air grown plants. The response of photosynthesis to O₂ indicated that the enhancement of growth and photosynthesis by CO₂ enrichment was a result of decreased photorespiration. Plants cultivated in low O₂ produced abnormal morphological features and after a short time showed a reduction in growth.     

The influence of temperature on glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and the regulation of these enzymes in a mesophilic and a thermophilic cyanobacterium

The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K _m's are for G6PDH: 80M (substrate) and 20M (NADP⁺); for 6PGDH: 90M (substrate) and 25M (NADP⁺). In Synechococcus 6716 the apparent K _m's are for G6PDH: 550M (substrate) and 30M (NADP⁺); for 6PGDH: 40M (substrate) and 10M (NADP⁺). None of the K _m's is influenced by the growth temperature and only the K _m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH glucose-6-phosphate, dehydrogenase - 6PGDH 6-phosphogluconate dehydrogenase - G6P glucose-6-phosphate - 6PG 6-phosphogluconate - RUDP ribulose-1,5-bisphosphate - Tricine N-Tris (hydroxymethyl)-methylglycine     

A re-assessment of bacterial growth efficiency: the heat production and membrane potential of Streptococcus bovis in batch and continuous culture

Glucose-limited, continuous cultures (dilution rate 0.1 h^-1) of Streptococcus bovis JB1 fermented glucose at a rate of 3.9 mol mg protein^-1 h^-1 and produced acctate, formate and ethanol. Based on a maximum ATP yield of 32 cells/mol ATP (Stouthamer 1973) and 3 ATP/glucose, the theoretical glucose consumption for growth would have been 2.1 mol mg protein^-1 h^-1. Because the maintenance energy requirement was 1.7 mol/mg protein/h (Russell and Baldwin 1979), virtually all of the glucose consumption could be explained by growth and maintenance and the Y_ATP was 30. Glucose-limited, continuous cultures produced heat at a rate of 0.29 mW/mg protein, and this value was similar to the enthalpy change of the fermentation (0.32 mW/mg protein). Batch cultures (specific growth rate 2.0 h^-1) fermented glucose at a rate of 81 mol mg protein^-1 h^-1, and produced only lactate. The heat production was in close agreement with the theoretical enthalpy change (1.72 versus 1.70 mW/mg protein), but only 80% of the glucose consumption could be accounted by growth and maintenance. The Y_ATP of the batch cultures was 25. Nitrogen-limited, glucose-excess, non-growing cultures fermented glucose at a rate of 6.9 mol mg protein^-1 h^-1, and virtually all of the enthalpy for this homolactic fermentation could be accounted as heat (0.17 mW/mg protein). The nitrogenlimited cultures had a membrane potential of 150 mV, and nearly all of the heat production could be explained by a futile cycle of protons through the cell membrane (watts = amperes x voltage where H⁺/ATP was 3). The membrane voltage of the nitrogen-limited cells was higher than the glucose-limited continuous cultures (150 versus 80 mV), and this difference in voltage explained why nitrogen-limited cultures consumed glucose faster than the maintenance rate. Batch cultures had a membrane potential of 100 mV, and this voltage could not account for increased glucose consumption (more than growth plus maintenance). It appears that another mechanism causes the increased heat production and lower growth efficiency of batch cultures.     

ATP formation coupled to caffeate reduction by H2 in Acetobacterium woodii NZva16

We have addressed the question, whether the reduction of caffeate in Acetobacterium woodii strain NZva16 is coupled to ATP synthesis by electron transport phosphorylation. The following results were obtained: 1. Cultures of A. woodii with H₂ and CO₂, grew to greater cell densities, when caffeate was also present. Caffeate was reduced to give hydrocaffeate and less acetate was formed. The cell yield based on the amount of caffeate reduced was approximately 1 g dry cells/mol. 2. Non-growing bacterial suspensions catalyzed the reduction of caffeate by H₂. The specific activity (0.2–1.0 mol · min^–1 · mg^–1 bacterial protein) was as high as expected for a catabolic reaction. 3. The ATP content of bacteria incubated, with H₂ increased from < 1 to about 7 mol per g cellular protein on the addition of caffeate. The ATP yield was calculated as 0.06 mol ATP · mol^–1 caffeate from the initial velocity of ATP formation and the activity of caffeate reduction. Valinomycin together with nigericin inhibited ATP formation and caused a 2–3-fold increase of the activity of caffeate reduction. Protonophores were without, effect. 4. Caffeate in the presence of H₂ caused the uptake of tetraphenylphosphonium cation by the bacteria. The uptake was abolished by valinomycin plus nigericin, and was considerably enhanced by monensin. Protonophores were without effect, even in the presence of monensin. It is concluded that caffeate reduction by H₂ is coupled to ATP formation by electron transport phosphorylation. However, the failure of protonophores to prevent phosphorylation and TPP uptake cannot be explained.Abbreviations Caffeate 3,4-Dihydroxycinnamate - Hydrocaffeate 3,4-dihydroxyphenylpropionate - TPP⁺ tetraphenylphosphonium cation - FCCP carbonylcyanide-4-trifluoromethoxyphenylhydrazone - TTGB 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazol - TCS 3,5,3,4-tetrachlorosalicylanilide     

Responses of nitrogen-fixing and nitrate-supplied alfalfa (Medicago sativa L.) to iron chelates in an alkaline hydroponic medium

Ferric ethylenediamine di-(o-hydroxyphenylacetate) (FeEDDHA) and ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) were evaluated as Fe sources for hydroponic growth of alfalfa (Medicago sativa L., cv. Mesilla), either dependent on N₂ fixation or supplied with NO₃. The hydroponic medium was maintained at pH 7.5 by addition of CaCO₃. Nitrogen-fixing cultures were inoculated with Rhizobium meliloti 102 F51 and grown in medium without added nitrogen. After five to seven weeks of growth under greenhouse conditions, plants were harvested. Nitrogen fixation was measured by the acetylene reduction method.When FeEDDHA was supplied, growth of alfalfa, whether dependent on N₂ fixation or supplied with NO₃, was severely limited at concentrations typically used in hydroponic medium (10 or 20 M). Maximum yield of NO₃-supplied alfalfa was obtained at 100 M while maximum yield of N₂-fixing alfalfa was obtained in the range of 33 to 200 M FeEDDHA. Nodule fresh weights and N₂ fixation rates increased with FeEDDHA concentration up to 33 M and remained essentially constant up to 200 M. With FeHEDTA, maximum yields of both NO₃-grown and N₂-fixing alfalfa were obtained at 10 M. Growth of NO₃-supplied plants was inhibited at 200 M FeHEDTA while growth of N₂-fixing plants was inhibited at 100 M FeHEDTA. The numbers of nodules per plant increased between 3.3 and 10 M FeHEDTA; however, inhibition of nodule formation occurred at a concentration of 33 M or higher. Nodule weights per plant and N₂ fixation rates were depressed at 3.3 M as well as at 100 M FeHEDTA. The results suggest that alfalfa dependent on N₂ fixation is more sensitive to limited Fe availability than alfalfa supplied with NO₃.     

Simultaneous influx of ammonium and potassium into maize roots: kinetics and interactions

The interaction between ammonium and potassium during influx was examined in roots of dark-grown decapitated corn seedlings (Zea mays L., cv. Pioneer 3369A). Influx was measured during a 10-min exposure to either (¹⁵NH₄)₂SO₄ ranging from 10 to 200 M NH ₄ ⁺ with and without 200 M K(⁸⁶Rb)Cl or to K(⁸⁶Rb)Cl ranging from 10 to 200 M K⁺ with and without 200 M NH ₄ ⁺ as (¹⁵NH₄)₂SO₄. The simple Michaelis-Menten model described the data well only for potassium influx in the presence of ambient ammonium. For the other three instances, the data were improved by assuming that a second influx mechanism became operative as the low-concentration phase approached saturation. Two distinct mechanisms are thus indicated for both ammonium and potassium influx within the range of 10 to 200 M.The influx mechanism operating at low concentrations showed greater affinity for potassium than for ammonium, even though the capacity for ammonium transport was twice as large as that for potassium. It is suggested that this phase involved a common transport system for the two ions and that localized low acidity next to the internal surface, following H⁺ extrusion, favored ammonium deprotonation and dissociation from the transport system-ammonium complex. Parallel decreases in V _max and increases in K_m of the low-concentration saturable phase occurred for ammonium influx when ambient potassium was present and for potassium influx when ambient ammonium was present. The data support a mixed-type inhibition in each case. Simultaneous measurement of potassium and ammonium influx showed that they were highly negatively correlated at the lower concentrations, indicating that the extent to which influx of the inhibited ion was restricted was associated with influx of the inhibitor ion. Presence of ambient ammonium eliminated the second phase of potassium influx. In contrast, the presence of ambient potassium decreased the concentration at which the second phase of ammonium influx was initiated but did not restrict the rate.Paper no. 11131 of the Journal Series of the North Carolina Agricultural Research ServiceThe use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned     

Growth parameters (K s, μmax,Y s) of Methanobacterium thermoautotrophicum

Methanobacterium thermoautotrophicum was grown on a mineral salts medium in a fermenter gassed with H₂ and CO₂, which were the sole carbon and energy sources. Under the conditions used the bacterium grew exponentially. The dependence of the growth rate () on the concentration of H₂ and CO₂ in the incoming gas and the dependence of the growth yield ( ) on the growth rate were determined at pH 7 (the pH optimum) and 65° C (the temperature optimum).The curves relating growth rate to the H₂ and CO₂ concentration were hyperbolic. From reciprocal plots apparent K _s values for H₂ and CO₂ and _max were obtained: app. = 20%; app. = 11%; = 0.69 h^-1; t (max)=1 h. was 1.6 g mol^-1 and almost independent of the growth rate, when the rate of methane formation was not limited by the supply of either H₂ or CO₂. The yield increased to near 3 g mol^-1 when H₂ or CO₂ were limiting. These findings indicate that methane formation and growth are less tightly coupled at high concentrations of H₂ or CO₂ in the medium than at low concentrations. The physiological significance of these findings is discussed. K _s: H₂ and CO₂ concentration supporting 0.5 _max; _max: specific growth rate at infinite substrate concentration; Y _s:growth yield (g dry weight/mol substrate); t : doubling time     

Energy requirements for growth and maintenance of Scenedesmus protuberans Fritsch in light-limited continuous cultures

Scenedesmus protuberans Fritsch was grown in light-limited continuous cultures with a light-dark cycle, at temperatures of 20° and 28° C. At 20° irradiances of 12 and 38 W m^–2 were used, at 28° 38 W m^–2.The relationships between growth rate and light uptake rate were of diphasic linear character. With the lower growth rates the relationships were defined with the parameters _e , i.e. the specific maintenance rate constant, and c, the true efficiency of light energy conversion into biomass. The _e -value was dependent on temperature, the c on irradiance.In cultures, incubated in prolonged darkness, decrease rates of biomass were comparable to the derived _e -values.Both diphasic linear relationships between growth rate and light uptake rate and the same order of magnitude of _e -values could be derived from literature data on other green algae.     

Different effects of inorganic and triethyl lead on growth and ultrastructure of lily pollen tubes

Summary Pollen tubes ofLilium longiflorum growingin vitro were treated for 1 h with inorganic lead (Pb) and with triethyl lead (TriEL) and studied by light and electron microscopy. Pb was considerably more toxic in relation to inhibition of pollen tube growth (EC₅₀=6 M Pb) than was TriEL (EC₅₀=60 M TriEL). On the other hand, at almost the entire concentration range tested (25-500 M) TriEL caused aberrant tubes and tube swellings. Pb did not cause tube swellings, even at highly growth-impairing concentrations. Pb (60 M) predominantly affected the ultrastructure of the growing cell walls without impairing the distribution of the cell organelles in the tube tips. In contrast, 50 and 100 M TriEL did not visibly influence cell wall ultrastructure but it severely damaged dictyosomes; 100 M TriEL also disturbed the original order of cell organelles in the tube tips. Cortical microtubules were selectively and completely destructed by TriEL at concentrations (50 M) where no effect on polar organization of the tube tips occurred but they remained unimpaired by 60 M Pb, indicating selective and effective interaction of TriEL with these cell organelles.Abbreviations EC⁵⁰ effective lead concentration causing 50% inhibition of pollen tube growth - MTs microtubules - Pb inorganic lead - TriAL trialkyl lead - TriEL triethyl lead     

Role of mitochondria in ethanol tolerance of Saccharomyces cerevisiae

The presence of active mitochondria and oxidative metabolism is shown to be essential to maintain low inhibition levels by ethanol of the growth rate (), fermentation rate (v) or respiration rate () of Saccharomyces cerevisiae wild type strain S288C. Cells which have respiratory metabolism show K _i (ethanol inhibition constant) values for , v and , higher (K _i>1 M) than those of petite mutants or grande strains grown in anaerobiosis (K _i=0.7 M). In addition, the relationship between or v and ethanol concentration is linear in cells with respiratory metabolism and exponential in cells lacking respiration. When functional mitochondria are transferred to petite mutants, the resulting strain shows K _i values similar to those of the grande strain and the inhibition of and v by increasing ethanol concentrations becomes linear.     

Effects of light on nitrate-limited Oscillatoria agardhii in chemostat cultures

The effects of the average light irradiance (I) on growth and nitrate uptake kinetics of the cyanobacterium Oscillatoria agardhii, in nitrate-limited chemostat cultures, were studied. Light was nonsaturating for I <9.4 Wm^–2, for all growth rates () studied. However, was throughout limited by the availability of nitrate. Under light-saturating conditions the kinetics of nitrate-limited growth could be adequately described by both the Monod and Droop equations. Under light-non-saturating conditions the internal nitrogen content (Q) was a function of both and I, for which new formulas were derived. The high uptake capacity (V _max) of nitrate-limited cells was independent of , but was significantly increased for cells growing at I <9.4 Wm^–2. The half-saturation constant for nitrate uptake (K _s ^u ) increased with increasing , but was independent of the prevailing light conditions. The effects of light during nitrate-limited growth were associated with the regulation in the nitrogen-containing pigments.The results reported herein have important consequences for the use of Q, K _s ^u and V _max values as indicators of nutrient-deficiency of natural populations.     

A continuous culture study of the bioenergetic aspects of growth and production of exocellular protease in Bacillus licheniformis

Summary Bacillus licheniformis S 1684 is able to produce an alkaline serine protease exocellularly. In glucose-limited chemostat cultures the specific rate of protease production was maximal at a -value of 0.22. Above this growth rate protease production was repressed. Dependent on 10–20% of the glucose input was used for exocellular product formation. The degree of reduction of exocellular products was 4.1.Maximum molar growth yields were high and indicate a high efficiency of growth. The values of Y _glu ^max and YO ₂ ^max were 83.8 and 53.3, respectively. When Y _glu ^max was corrected for the amount of glucose used for product formation a value of 100.3 was obtained. These high maximum molar growth yields are most probably caused by a high Y _ATP ^max . Anaerobic batch experiments showed a Y _ATP of 14.6.Sometimes the used strain was instable in cell morphology and protease production. Non-protease producing cells most probably develop from producing cells by mutation in the rel-gene. Producing cells most probably are relaxed (rel ^-) and non-producing cells stringent (rel ⁺).Glossary specific growth rate (h^-1) - Y _sub growth yield permol substrate (g biomass/mol) - Y ^max maximum molar growth yield, corrected for maintenance requirements (g biomass/mol) - Y ^max(corr) Y ^max corrected for product formation (g biomass/mol) - m _sub maintenance requirements (mol/g biomass·h) - m _sub(corr) maintenance requirements corrected for product formation (mol/g biomass·h) - Y _c fraction of organic substrate converted in biomass - z fraction of organic substrate converted in exocellular products - d fraction of organic substrate converted in CO₂ (g mol/g atom C) - Crec% carbon recovery % - average degree of reduction of exocellular products - P/O amount of ATP produced during electron-transport of 2 electrons to oxygen     

Blood-gas,acid-base and catecholamine responses to lactic acid infusion in larval and adult Ambystoma tigrinum

Larval and adult Ambystoma tigrinum were subjected to acidosis by infusing lactic acid (2 M·g^-1) into the peritoneal cavity. Blood was sampled at intervals to establish the time-course of the ensuing acidosis. Both larvae and adults became significantly acidotic after 1 h. The larval acidosis was more pronounced (-4 pH units versus-2 pH units) than adults due to greater extracellular buffering capacity (higher [HCO₃ ^-]) in adults. Both forms recovered in about 8 h. Larvae showed a typical increase in circulating norepinephrine during the initial stages of the acidosis; adults did not, having significantly lower norepinephrine titer than larvae during the acidosis. Both larvae and adults showed transient increases in PO₂ during the acidosis. The ₁ and ₂ antagonists, timolol and butoxamine respectively, (0.2 g·g^-1) were administered to separate groups of larvae. Butoxamine (₂) delayed the recovery from the acidosis by prolonging the increase in arterial PCO₂ and reversing the recovery of [HCO₃ ^-]. Timolol (₁) did not delay recovery. We conclude that ₂ receptors are involved in the catecholamine responses to acidosis in larvae. Catecholamines appear not to play the same role in adult acid-base disturbances as they seem to in larvae.Abbreviations RBC red blood cell     

Different Ks values for hydrogen of methanogenic bacteria and sulfate reducing bacteria: An explanation for the apparent inhibition of methanogenesis by sulfate

Desulfovibrio vulgaris (Marburg) and Methanobrevibacter arboriphilus (AZ) are anaerobic sewage sludge bacteria which grow on H₂ plus sulfate and H₂ plus CO₂ as sole energy sources, respectively. Their apparent K_s values for H₂ were determined and found to be approximately 1 M for the sulfate reducing bacterium and 6 M for the methanogenic bacterium. In mixed cell suspensions of the two bacteria (adjusted to equal V _max) the rate of H₂ consumption by D. vulgaris was five times that of M. arboriphilus, when the hydrogen supply was rate limiting. The apparent inhibition of methanogenesis was of the same order as expected from the different K_s values for H₂. Difference in substrate affinities can thus account for the inhibition of methanogenesis from H₂ and CO₂ in sulfate rich environments, where the H₂ concentration is well below 5 M.     

Copper but not iron limitation increases astaxanthin production by Phaffia rhodozyma in a chemically defined medium

The influence of copper (0–32 M) and iron (0–108 M) on growth and astaxanthin production by Phaffia rhodozyma was studied. Copper below 3.2 M increased the astaxanthin content of the cells (from 220 to 287 g g^–1) but at the expense of a slightly decreased growth (from 11.3 to 10.2 mg ml^–1). In contrast, iron below 1 M decreased both the growth and astaxanthin content of the cells. Using copper limitation instead of toxic respiratory inhibitors to improve astaxanthin production has obvious advantages from the product quality, environmental and process operation points of view.     

Adenylate effects on protein phosphorylation in the interenvelope lumen of pea chloroplasts

A 64-kilodalton (kDa) protein, situated in the lumen between the inner and outer envelopes of pea (Pisum sativum L.) chloroplasts (Soll and Bennett 1988, Eur. J. Biochem., 175, 301–307) is shown to undergo reversible phosphorylation in isolated mixed envelope vesicles. It is the most conspicuously labelled protein after incubation of envelopes with 33 nmol·1^-1 [-³²P]ATP whereas incubation with 50 mol·1^-1 [-³²P]ATP labels most prominently two outer envelope proteins (86 and 23 kDa). Half-maximum velocity for phosphorylation of the 64-kDa protein occurs with 200 nmol·1^-1 ATP, and around 40 mol·1^-1 ATP for phosphorylation of the 86- and 23-kDa proteins, indicating the operation of two distinct kinases. GGuanosine-, uridine-, cytidine 5-triphosphate and AMP are poor inhibitors of the labelling of the 64-kDa protein with [-³²P]ATP. On the other hand, ADP has a potent influence on the extent of labelling (half-maximal inhibition at 1–5 mol·1^-1). The ADP-dependent appearance of ³²P in ATP indicates that ADP acts by reversal of kinase activity and not as a competitive inhibitor. However, the most rapid loss of ³²P from pre-labelled 64-kDa protein occurs when envelope vesicles are incubated with ATP t1/2=15 s at 20 molsd1^-1 ATP). This induced turnover of phosphate appears to be responsible for the rapid phosphoryl turnover seen in situ.Abbreviations LHCP ligh-harvesting chlorophyll-a/b-binding protein - S_0.5 concentration giving half-maximal phosphorylation - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine