Ammonium and nitrate as nitrogen sources in two Eriophorum species

Summary We compared ammonium and nitrate nutrition in Eriophorum scheuchzeri and E. vaginatum, two Alaskan sedges that are native to high- and low-fertility sites, respectively. When grown in solution culture, the two species were similar in their kinetics of NH _inf4 ^sup+ NO _inf3 ^sup- absorption: at nitrogen concentrations below 50 M, net NH _inf4 ^sup+ and NO _inf3 ^sup- were absorbed at similar rates, but at higher concentrations, net uptake of NO _inf3 ^sup- was significantly faster than that of NH _inf4 ^sup+ . The two species also showed similar abilities to assimilate NO _inf3 ^sup- . Growth of E. vaginatum under NO _inf3 ^sup- nutrition was only slightly less than that under NH _inf4 ^sup+ . The observed similarities between these species from contrasting edaphic habitats indicate that factors other than tissue-specific rates of nitrogen acquisition and assimilation may underlie local adaptation to soil N fertility. Moreover, the capacity of these species to exploit NO _inf3 ^sup- as a N source supports the view that NO _inf3 ^sup- availability may be significant even in wet, acidic, arctic soils.     

Effects of fire and harvesting on nitrogen transformations and ionic mobility in soils of Eucalyptus regnans forests of south-eastern Australia

Summary Effects of fire and forest harvesting on inorganic-N in the soil, on net N-mineralization, and on the leaching of NO _inf3 ^sup- -N and metallic cations were measured in forests of Eucalyptus regnans following a severe wildfire in 1983. E. regnans regenerates profusely by seed after fire, and this study compared unburnt forest with forests burnt at varying intensities (surface fire and crown fire), and with logged and burnt forest (slash fire). Total inorganic-N in soil (0–5 cm) increased with increasing fire intensity to a maximum of 158 g g^-1 in the slash fire plot (compared with 51 g g^-1 in the unburnt forest) over the first 205 days after fire. Total inorganic-N returned to a concentration equal to that in the unburnt forest after 485 days at the slash fire plot, and after only 205 days at the surface fire plot. Studies of net mineralization in situ and of NO _inf3 ^sup- -N in soil solution support the hypothesis that inorganic-N was immobilized in all of the burnt forests; microbial immobilization after fire is identified as a key process in N-conservation, limiting the substrate available for nitrification and thereby limiting the loss of N from the system by leaching. The concentrations of NO _inf3 ^sup- -N and metallic cations in soil solution increased with increasing fire intensity. For the first 318 days after the fire, [NO _inf3 ^sup- -N] in soil solution at 10 cm averaged 0.6 g ml^-1 in the unburnt forest, 9.7 mg l^-1 in the surface fire plot, 26 mg l^-1 in the crown fire plot, and 70 mg l^-1 in the slash fire plot. The concentration of metallic cations in soil solution was significantly correlated with [NO _inf3 ^sup- -N], the observed order of mobility being Ca²⁺>Mg²⁺>K⁺>Na⁺. Processes which limit the production and persistence of NO _inf3 ^sup- -N in soil solution following disturbance will significantly reduce nutrient losses or redistribution.     

Energetics and regulations of formate and hydrogen metabolism by Methanobacterium formicicum

Accumulation of formate to millimolar levels was observed during the growth of Methanobacterium formicicum species on H₂–CO₂. Hydrogen was also produced during formate metabolism by M. formicicum. The amount of formate accumulated in the medium or the amount H₂ released in gas phase was influenced by the bicarbonate concentration. The formate hydrogenlyase system was constitutive but regulated by formate. When methanogenesis was inhibited by addition of 2-bromoethane sulfonate, M. formicicum synthesized formate from H₂ plus HCO _inf3 ^sup- or produced H₂ from formate to a steady-state level at which point the Gibbs free energy (G) available for formate synthesis or H₂ production was approximately -2 to -3 kJ/reaction. Formate conversion to methane was inhibited in the presence of high H₂ pressure. The relative rates of conversion of formate and H₂ were apparently controlled by the G available for formate synthesis, hydrogen production, methane production from formate and methane production from H₂. Results from ¹⁴C-tracer tests indicated that a rapid isotopic exchange between HCOO^- and HCO _inf3 ^sup- occurred during the growth of M. formicicum on H₂–CO₂. Data from metabolism of ¹⁴C-labelled formate to methane suggested that formate was initially split to H₂ and HCO _inf3 ^sup- and then subsequently converted to methane. When molybdate was replaced with tungstate in the growth media, the growth of M. formicicum strain MF on H₂–CO₂ was inhibited although production of methane was not Formate synthesis from H₂ was also inhibited.     

Effect of dissolved inorganic carbon on the expression of carboxysomes,localization of Rubisco and the mode of inorganic carbon transport in cells of the cyanobacterium Synechococcus UTEX 625

In the cyanobacterium Synechococcus UTEX 625, the extent of expression of carboxysomes appeared dependent on the level of inorganic carbon (CO₂+HCO _inf3 ^sup- ) in the growth medium. In cells grown under 5% CO₂ and in those bubbled with air, carboxysomes were present in low numbers (<2 · longitudinal section^-1) and were distributed in an apparently random manner throughout the centroplasm. In contrast, cells grown in standing culture and those bubbled with 30 l CO₂ · 1^-1 possessed many carboxysomes (>8 · longitudinal section^-1). Moreover, carboxysomes in these cells were usually positioned near the cell periphery, aligned along the interface between the centroplasm and the photosynthetic thylakoids. This arrangement of carboxysomes coincided with the full induction of the HCO _inf3 ^sup- transport system that is involved in concentrating inorganic carbon within the cells for subsequent use in photosynthesis. Immunolocalization studies indicate that the Calvin cycle enzyme ribulose bisphosphate carboxylase was predominantly carboxysome-localized, regardless of the inorganic carbon concentration of the growth medium, while phosphoribulokinase was confined to the thylakoid region. It is postulated that the peripheral arrangement of carboxysomes may provide for more efficient photosynthetic utilization of the internal inorganic carbon pool in cells from cultures where carbon resources are limiting.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon (CO₂+HCO _inf3 ^sup- +CO _inf3 ^sup2- ) - PRK phosphoribulokinase - RuBP ribulose 1,5-bisphosphate - Rubisco LS large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase     

Non-mycorrhizal uptake of amino acids by roots of the alpine sedge Kobresia myosuroides: implications for the alpine nitrogen cycle

Non-mycorrhizal plants of the alpine sedge, Kobresia myosuroides, take up the amino acid glycine from nutrient solutions at greater rates than NO _inf3 ^sup- or NH _inf4 ^sup+ . The amino acids glutamate and proline were also taken up at high rates. Total plant biomass was twice as high after 4 months of growth on glycine, compared to NH₄NO₃, with significant increases in both root and leaf biomass. By taking advantage of differences in the ¹³C signature of air in the growth chamber and the glycine used for growth, a two-member mixing model was used to estimate that a significant amount of the glycine was taken up as intact molecules, enough to contribute 16% of the total carbon assimilation over a 4-month growing period. Glycine uptake was inhibited when roots were exposed to N₂ in place of air, and when the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) was added to the root solution. From these results it is concluded that glycine uptake occurs through active transport. Glycine uptake exhibited a Q₁₀ of 2.0 over the temperature range 5–15° C, with relatively high rates maintained at the lowest temperature measured (5° C). Roots of Kobreasia were not capable of taking up NH _inf4 ^sup+ at measureable rates. To our knowledge, this is the first report of a plant whose non-mycorrhizal roots cannot take up NH _inf4 ^sup+ . Measurements of three N fractions (NO _inf3 ^sup- , NH _inf4 ^sup+ , and total amino acids) in the soil pore water were made over two growing seasons in two Kobresia dry meadows using microlysimeters. At the West Knoll site, which is characterized by soils with average amounts of organic matter, the dominant forms of N in the soil pore water were NO _inf3 ^sup- and NH _inf4 ^sup+ (0–450 mol L^-1). Amino acid concentrations were generally less than 20 mol L^-1 at this site. At the East Knoll site, which is characterized by soils with higher than average amounts of organic matter, amino acids were generally present at higher concentrations (17–100 mol L^-1), compared to NO _inf3 ^sup- and NH _inf4 ^sup+ . The most abundant amino acids were glycine (10–100 mol L^-1), glutamate (5–70 mol L^-1), and late in the season cystein (5–15 mol L^-1). The results demonstrate that this sedge, which dominates dry meadow communities in many alpine ecosystems, is capable of taking up intact amino acids as a principal N source, and has access to high amino acid concentrations in certain alpine soils. Such uptake of organic N may accommodate plant N demands in the face of slow alpine N mineralization rates due to cold soil temperatures.     

The reduction of nitrous oxide to dinitrogen by Escherichia coli

Escherichia coli K12 reduces nitrous oxide stoichiometrically to molecular nitrogen with rates of 1.9 mol/h x mg protein. The activity is induced by anaerobiosis and nitrate. N₂+formation from N₂O is inhibited by C₂H₂ (K _i 0.03 mM in the medium) and nitrite (K _i=0.3 mM) but not by azide. A mutant defective in FNR synthesis is unable to reduce N₂O to N₂. The reaction in the wild type could routinely be followed by gas chromatography and alternatively by mass spectrometry measuring the formation of ¹⁵N₂ from ¹⁵N₂O. The enzyme catalyzing N₂O-reduction in E. coli could not be identified; it is probably neither nitrate reductase nor nitrogenase. E. coli does not grow with N₂O as sole respiratory electron acceptor. N₂O-reduction might not have a physiological role in E. coli, and the enzyme involved might catalyze something else in nature, as it has a low affinity for the substrate N₂O (apparent K _m3.0 mM). The capability for N₂O-reduction to N₂ is not restricted to E. coli but is also demonstrable in Yersinia kristensenii and Buttiauxella agrestis of the Enterobacteriaceae. E. coli is able to produce NO and N₂O from nitrite by nitrate reductase, depending on the assay conditions. In such experiments NO _inf2 ^sup- is not reduced to N₂ because of the high demand for N₂O of N₂O-reduction and the inhibitory effect of NO _inf2 ^sup- on this reaction.Dedicated to Professor L. Jaenicke, Köln, on the occassion of his 70th birthday     

Localization of hydrogenase and nitrate reductase in Campylobacter sputorum subsp. bubulus

Campylobacter sputorum subsp. bubulus contained hydrogenase activity after growth with lactate and nitrate and after growth with hydrogen and nitrate. After growth with hydrogen and nitrate a molar growth yield (g dry cells/mol hydrogen) of 5.6 was measured. Hydrogenase and nitrate reductase were membrane-bound enzymes. In cells with high hydrogenase activity the H⁺/O, H⁺/NO _inf2 ^sup- and H⁺/NO _inf3 ^sup- values with hydrogen as the electron donor were 3.74, 2.61 and 4.36 respectively. In cells with low hydrogenase activity these values were 2.33,-0.86 and 1.31 respectively. These values and the stoichiometry of respiration-driven proton translocation (H⁺/2e=2) led to the conclusion that hydrogenase is located at the periplasmic side of the cytoplasmic membrane. In cells with low lactate dehydrogenase activity or low hydrogenase activity the reduction of nitrate to nitrite could be separated from the reduction of nitrite to ammonia. Positive H⁺/NO _inf3 ^sup- values (between 0.9 and 1.7) with lactate or hydrogen as the electron donor were measured in these cells whereas H⁺/NO _inf2 ^sup- values were negative. From this result it was concluded that nitrate reductase is located at the cytoplasmic face of the cytoplasmic membrane. The results explain the previous observation that molar growth yields with nitrate were somewhat higher than those with nitrite.     

Isolation and characterization of a thermophilic benzoate-degrading,sulfate-reducing bacterium,Desulfotomaculum thermobenzoicum sp. nov.

A new thermophilic sulfate-reducing bacterium, strain TSB, that was spore-forming, rod-shaped, slightly motile and gram-positive, was isolated from a butyrate-containing enrichment culture inoculated with sludge of a thermophilic methane fermentation reactor. This isolate could oxidize benzoate completely. Strain TSB also oxidized some fatty acids and alcohols. SO _inf4 ^sup2- , SO _inf3 ^sup2- , S₂O _inf3 ^sup2- and NO _inf3 ^sup- were utilized as electron acceptors. With pyruvate or lactate the isolate grew without an external electron acceptor and produced acetate. The optimum temperature for growth was 62°C. The G+C content of DNA was 52.8 mol%. This isolate is described as a new species, Desulfotomaculum thermobenzoicum.     

Dissimilatory hexaheme c nitrite reductase of “Spirillum” strain 5175: purification and properties

When grown with nitrate as terminal electron acceptor both the soluble (periplasm, cytoplasm) and the membrane fraction of Spirillum strain 5175 exhibited high nitrite reductase activity. The nitrite reductase obtained from the soluble fraction was purified 76-fold to electrophoretical homogeneity. The enzyme reduced nitrite to ammonia with a specific activity of 723 mol NO _inf2 ^sup- × (mg protein × min)^-1. The molecular mass was 58±1 kDa by SDS-PAGE compared to 59±2 kDa determined by size exclusion chromatography under nondenaturing conditions. The enzyme (as isolated) contained 5.97±0.15 heme c molecules/M_r 58 kDa. The absorption spectrum was typical for c-type cytochrome with maxima at 280, 408, 532 and 610 nm (oxidized) and at 420, 523 and 553 nm (dithionite-reduced). The enzyme (as isolated) exhibited a complex set of high-spin and lowspin ferric heme resonances with g-values at 9.82, 3,85, 3.31, 2.95, 2.30 and 1.49 in agreement with data reported for electron paramagnetic resonance spectra of nitrite reductases from Desulfovibrio desulfuricans, Wolinella succinogenes and Escherichia coli.Abbreviations DNRA dissimilatory nitrate reduction to ammonia - EPR electron paramagnetic resonance - PAGE polyacrylamide gel electrophoresis - NaP_i sodium phosphate - SDS sodium dodecylsulfate     

Synthetic peptide VKGFY and its cyclic analog stimulate macrophage bactericidal activity through non-opioid beta-endorphin receptors

We synthesized linear and cyclic pentapeptides corresponding to the sequence 369-373 of human immunoglobulin G heavy chain—VKGFY (referred to as pentarphin and cyclopentarphin, respectively). The effect of pentarphin and cyclopentarphin on phagocytosis of Salmonella typhimurium virulent 415 strain bacteria by mouse peritoneal macrophages in vitro was studied. Control experiments showed that macrophages actively captured these bacteria, but did not digest them: the captured microbes were viable and continued to proliferate inside the phagocytes; within 12 h all macrophage monolayer was destroyed (incomplete phagocytosis). If 1 nM pentarphin or cyclopentarphin was added to the cultivation medium, macrophage bactericidal activity was significantly increased and they digested all captured microorganisms within 6 h (complete phagocytosis). To study the receptor binding properties of pentarphin and cyclopentarphin we prepared ¹²⁵I-labeled pentarphin (179 Ci/mmol specific activity). The binding of ¹²⁵I-labeled pentarphin to mouse peritoneal macrophages was highaffinity (K _d = 3.6 ± 0.3 nM) and saturable. Studies on binding specificity revealed that this binding was insensitive to naloxone and [Met⁵]enkephalin, but completely inhibited by unlabeled cyclopentarphin (K _i = 2.6 ± 0.3 nM), immunorphin (K _i = 3.2 ± 0.3 nM), and -endorphin (K _i = 2.8 ± 0.2 nM). Thus, the effects of pentarphin and cyclopentarphin on macrophages are mediated by naloxone-insensitive receptors common for pentarphin, cyclopentarphin, immunorphin, and -endorphin.     

The influence of salinity on the kinetics of NH inf4 sup+ uptake in Spartina alterniflora

Summary The effects of short- and long-term exposure to a range in concentration of sea salts on the kinetics of NH _inf4 ^sup+ uptake by Spartina alterniflora were examined in a laboratory culture experiment. Long-term exposure to increasing salinity up to 50 g/L resulted in a progressive increase in the apparent K_m but did not significantly affect V_max (mean V_max=4.23±1.97 mole·g^–1·h^–1). The apparent K_m increased in a nonlinear fashion from a mean of 2.66±1.10 mole/L at a salinity of 5 g/L to a mean of 17.56±4.10 mole/L at a salinity of 50 g/L. These results suggest that the long-term effect of exposure to total salt concentrations within the range 5–50 g/L was a competitive inhibition of NH _inf4 ^sup+ uptake in S. alterniflora. No significant NH _inf4 ^sup+ uptake was observed in S. alterniflora exposed to 65 g/L sea salts. Short-term exposure to rapid changes in salinity significantly affected both V_max and K_m. Reduction of solution salinity from 35 to 5 g/L did not change V_max but reduced K_m by 71%. However, exposing plants grown at 5 g/L salinity to 35 resulted in an decrease in V_max of approximately 50%. Exposure of plants grown at 35 g/L to a total sea salt concentration of 50 g/L for 48h completely inhibited uptake of NH _inf4 ^sup+ . For both experiments, increasing salinity led to an increase in the apparent K_m similar to that found in response to long-term exposure. Our data are consistent with a conceptual model of changes in the productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH _inf4 ^sup+ uptake kinetics.     

Ethane production by Methanosarcina barkeri during growth in ethanol supplemented medium

Methanosarcina barkeri strain 227 produced ethane during growth on H₂/CO₂ when ethanol was added to the medium in concentrations of 89–974 mM; ethane production varied from 14 to 38 nmoles per tube (20 ml gas phase, 5.7 ml liquid) with increasing ethanol concentrations. Cells grown to mid-logarithmic phase (A₆₀₀ 0.46, protein = 64 g/ml) on H₂/CO₂, thoroughly flushed with H₂/CO₂, then exposed to ethanol, produced maximal ethane levels (at 585 and 974 mM ethanol) of about 215 nmoles per tube, with an ethane/methane ratio of 1×10^-3. Mid-logarithmic-phase cultures of Methanosarcina barkeri strain Fusaro also produced ethane (up to 20 nmoles per tube) when exposed to ethanol. Cultures of strain 227 growing on methanol in the absence of H₂ produced 6 nmoles per tube of ethane when supplemented with ethanol whereas those lacking ethanol but containing H₂ and/or methanol produced 1.6 nmoles per tube. Cultures of Methanococcus deltae strains LH and RC, Methanospirillum hungatei or Methanobacterium thermoautotrophicum produced 5 nmoles ethane per tube when grown in medium containing ethanol. Ethanol concentrations of 177–886 mM were inhibitory to growth of all methanogens examined. Production of ethane by Methanosarcina was inhibited by >62 mM methanol, and both methanogenic inhibitors tested, CCl₄ and Br–CH₂–CH₂–SO _inf3 ^sup- , inhibited ethane and methane production concurrently. The data suggest that ethanol is converted to ethane by Methanosarcina species using the terminal portion of the methanol-to-methane pathway.     

Nitrogen and phosphorus uptake by the Brazilian kelp Laminaria abyssalis (Phaeophyta) in culture

The uptake of ammonium, nitrate and phosphate by laboratory-grown young sporophytes of Laminaria abyssalis was measured in a perturbed system (batch mode) at 18 °C and 35 ± 5 µE m^–2 s^–1 photon flux density. Uptake of all appeared to follow saturation-type nutrient uptake kinetics. The NO _inf3 ^sup– (K _s = 14.0 µM, V _max = 5.0 µmol h^–1 g^–1 dry wt) and NH _inf4 ^sup+ (K _s = 4.6 µM, V _max= 2.0 µmol h^–1 g^–1 dry wt) were taken up simultaneously, although NH _inf4 ^sup+ was taken up more rapidly. Values of K ₃ and V _max for phosphate were, respectively, 2.21 µM and 0.83 µmol h^–1 g^–1 dry wt. Nitrate and phosphate were both consumed in similar rates (V _max /Ks 0.37) at low concentrations. NH _inf4 ^sup+ , thus, might be a more efficient form of N fertilizer if artificial enrichment of seawater is used.     

Superoxide production by thylakoids during chilling and its implication in the susceptibility of plants to chilling-induced photoinhibition

Factors influencing the rate of superoxide (O ₂ ^- ) production by thylakoids were investigated to determine if increased production of the radical was related to injury induced by chilling at a moderate photon flux density (PFD). Plants used were Spinacia oleracea L., Cucumis sativus L. and Nerium oleander L. grown at either 200° C or 45° C. Superoxide production was determined by electron-spin-resonance spectroscopy of the (O ₂ ^- )-dependent rate of oxidation of 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidine (OXANOH) to the corresponding oxazolidinoxyl radical, OXANO ·. For all plants, the steady-state rate of O ₂ ^- production by thylakoids, incubated at 25° C and 350 mol photon · m^–2 · s^–1 (moderate PFD) with added ferredoxin and NADP, was between 7.5 and 12.5 mol · (mg chlorophyll)^–1 · h^–1. Incubation at 5° C and a moderate PFD, decreased the rate of O ₂ ^- production 40% and 15% by thylakoids from S. oleracea and 20° C-grown N. oleander, chillinginsensitive plants, but increased the rate by 56% and 5% by thylakoids from C. sativus and 45° C-grown N. oleander, chilling-sensitive plants. For all plants, the addition of either ferredoxin or methyl viologen increased the rate of O ₂ ^- -production at 25° C by 75–100%. With these electron acceptors, lowering the temperature to 5° C caused only a slight decrease in O ₂ ^- production. In the absence of added electron acceptors, thylakoids produced O ₂ ^- at a rate which was about 45% greater than that when ferredoxin and NADP were present. The addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea reduced O ₂ ^- production under all conditions tested. The results show that the rate of O ₂ ^- production increases in thylakoids when the rate of electron transfer to NADP is reduced. This could explain differences in the susceptibility of thylakoids from chilling-sensitive and chilling-insensitive plants to chilling at a moderate PFD, and is consistent with the proposal that O ₂ ^- production is involved in the injury leading to the inhibition of photosynthesis induced under these conditions.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophen-yl)-1,1-dimethylurea - Fd ferredoxin - MV methyl viologen - 20°oleander Nerium oleander grown at 20° C - 45°-oleander N. oleander grown at 45° C - OXANOH 2-ethyl-1-hydroxy-2,5,5-tri-methyl-3-oxazolidine - PFD photon flux density (photon fluence rate) - TEMED tetramethyl ethylenediamine We would like to thank R.T. Furbank, R.S.B.S., Australian National University, Canberra, A.C.T., and C.B. Osmond, now of Duke University, Durham, N.C., USA, for the gift of ferredoxin, R.A.J.H. was supported by a Commonwealth Postgraduate Research Award.     

Purification and characterization of membrane-bound hydrogenase from Methanosarcina barkeri MS

Hydrogenase was solubilized from the membrane of acetate-grown Methanosarcina barkeri MS and purification was carried out under aerobic conditions. The enzyme was reactivated under reducing conditions in the presence of H₂. The enzyme showed a maximal activity of 120±40 mol H₂ oxidized · min^–1 · min^–1 with methyl viologen as an electron acceptor, a maximal hydrogen production rate of 45±4 mol H₂ · min^–1 · mg^–1 with methyl viologen as electron donor, and an apparent K _m for hydrogen oxidation of 5.6±1.7 M. The molecular weight estimated by gel filtration was 98,000. SDS-PAGE showed the enzyme to consist of two polypeptides of 57,000 and 35,000 present in a 1:1 ratio. The native protein contained 8±2 mol Fe, 8±2 mol S^2–, and 0.5 mol Ni/mol enzyme. Cytochrome b was reduced by hydrogen in a solubilized membrane preparation. The hydrogenase did not couple with autologous F₄₂₀ or ferredoxin, nor with FAD, FMN, or NAD(P)⁺. The physiological function of the membrane-bound hydrogenase in hydrogen consumption is discussed.Abbreviation CoM-S-S-HTP the heterodisulfide of 7-mercaptoheptanoylthrconine phosphate and coenzyme M (mercaptoethanesulfonic acid)     

Biochemical studies on the lethal effects of solar and artificial ultraviolet radiation on Staphylococcus aureus

The effects of UV-B radiation generated in the laboratory and as a component of sunlight on the viability and particular biochemical activities of the bacterium Staphylococcus aureus have been examined. UV-B radiation progressively inhibits protein synthesis (assayed as ³H-alanine incorporation) and kills cells. Cell respiration, and RNA and DNA synthesis (³H-uridine and ³H-thymidine incorporation) were not greatly affected by UV-B irradiation. The OH and ¹O₂-free radical scavengers protected cells against killing and inhibition of protein synthesis by UV-B, suggesting that such radicals mediate the effects of UV-B on this organism. A similar protective effect using a ferric ion chelator suggests an important role for metallic ions in UV-B lethality.Abbreviations VIS, UV-A, UV-B, UV-C radiation in the bands 400–750 nm, 315–400 nm, 280–315 nm, 200–280 nm respectively - DBCO diazabicyclooctane - OFR oxygen free radical - OH, ¹O₂, O _inf2 ^sup- hydroxyl free radical, singlet oxygen, superoxide radical respectively     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Enzyme localization and orientation of the active site of dissimilatory nitrite reductase from Bacillus firmus

The location of the dissimilatory nitrite reductase and orientation of its reducing site of the Grampositive denitrifier, Bacillus firmus NIAS 237 were examined. Approximately 90% of the total dissimilatory nitrite reductase activity with ascorbate-reduced phenazine methosulfate (PMS) as the electron donor was on the protoplast membrane. Nitrite induced with intact Bacillus cells an alkalinization in the external medium, followed by acidification. The electron transfer inhibitor, 2-heptyl-4-hydroxyquinoline-N-oxide, which blocked nitrite reduction with endogenous substrates, inhibited the acidification, but not the alkalinization. Alkalinization was not affected with ascorbate-reduced PMS as the artificial electron donor. This indicated that the alkalinization is not associated with proton consumption outside the cytoplasmic membrane by the extracellular nitrite reduction. The dissimilatory nitrite reductase of B. firmus NIAS 237 was located on the cytoplasmic membrane, and its reducing site is suggested to be on the inner side of this membrane.Abbreviations CCCP carbonylcyanide m-chlorophenylhydrazone - HOQNO 2-heptyl-4-hydroxyquinoline-N-oxide - PMS phenazine methosulfate - H⁺/NO _inf2 ^sup- ratio number of consumed protons in the external medium per one ion of NO _inf2 ^sup- reduced     

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     

Improvement on laboratory fermentation equipment to study Saccharomyces cerevisiae metabolism

Beside being an ordinary fermenter, the present equipment was conceived to sample the medium, to store the samples and to record photographs of the yeasts. Ten sensors were used to measure gas exchanges. During the growth of ScM1 (a Saccharomyces cerevisiae strain) on glucose, we could observe two different linear decreases of CO₂ production rates (18.17±0.12 mmol CO₂ h^–2 (g biomass)^–1 and 8.67±0.12 mmol CO₂ h^–2 (g biomass)^–1), together with a sudden variation of slope during the respiro-fermentative phase. Nomenclature F_in InletairFlowl h ^–1 F_out OutletgasFlowl h ^–1 _in Inletairtemperature°C_out Outletgastemperature°CP _atm AtmosphericPressuremmHgP _in InletairOverPressuremmHgP _out OutletgasOverPressuremmHgDODissolvedO ₂ mg l^–1 pO₂ PartialPressureO ₂ in Outlet gas % (v/v) pCO₂ PartialPressureCO ₂ in Outlet gas % (v/v) Int(t) Whole number of hours