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1.
Uptake of phosphate in the light by Amphidinium carterae, Amphidinium klebsii, cultured and symbiotic Gymnodinium microadriaticum conformed to Michaelis-Menten type saturation kinetics with all organisms showing similar K m values, namely 0.005 to 0.016 M phosphorus. V max values were 0.009–0.32 nmol phosphorus · 105 cells-1 · 10 min-1. Phosphate uptake by all the dinoflagellates was greater in the dark than in the light. The metabolic inhibitor 3-(3,4-dichlorophenyl) 1,1-dimethylurea stimulated phosphate uptake in the light by A. carterae and A. klebsii, but inhibited uptake by cultured and symbiotic G. microadriaticum. Carbonylcyanide 3-chlorophenylhydrazone (CCCP) inhibited phosphate uptake by A. carterae and A. klebsii under both light and dark conditions. Uptake of phosphate by cultured and symbiotic G. microadriaticum in the light, but not in the dark, was inhibited by CCCP. Low concentrations of arsenate (5 g As · l-1) stimulated phosphate by A. carterae and A. klebsii, but inhibited uptake by cultured and symbiotic G. microadriaticum. High concentrations of arsenate (100 g As · l-1) did not affect uptake of phosphate by A. carterae and A. klebsii.  相似文献   

2.
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.  相似文献   

3.
Fluorescent Pseudomonas sp. strain 267 promotes growth of nodulated clover plants under gnotobiotic conditions. In the growth conditions (60 M FeCl3), the production of siderophores of the pseudobactin-pyoverdin group was repressed. Plant growth enhancement results from secretion of B vitamins by Pseudomonas sp. strain 267. This was proven by stimulation of clover growth by naturally auxotrophic strains of Rhizobium leguminosarum bv. trifolii and marker strains E. coli thi- and R. meliloti pan- in the presence of the supernatant of Pseudomonas sp. strain 267. The addition of vitamins to the plant medium increased symbiotic nitrogen fixation by the clover plants.  相似文献   

4.
A method for plant regeneration of Iris via somatic embryogenesis is described. Root and leaf pieces from in vitro-grown plants of several genotypes of rhizomatous Iris sp. were cultured in vitro. Callus induction occurred only on root cultures incubated under low light intensity (35 mol m-2 s-1) on two induction media containing 2,4-D (4.5 or 22.5 M), NAA (5.4 M) and kinetin (0.5 M). Somatic embryos developed after transfer of callus onto four regeneration media containing 9 or 22 M BA, or 5 M kinetin and 2 M TIBA or 9 M BA and 4 M TIBA. Plantlets could be obtained from these somatic embryos. Genotypic differences were found both in callus induction and somatic embryo formation, with I. pseudacorus responding better than I. versicolor or I. setosa. Cytological analysis performed on root tips of 80 regenerated plants revealed that two of the I. pseudacorus regenerants were tetraploid.Abbreviations 2,4-D dichlorophenoxy acetic acid - NAA naphthaleneacetic acid - BA 6-benzyladenine - TIBA 2,3,5-triiodobenzoic acid - IBA indolebutyric acid  相似文献   

5.
High molecular weight lectins (> 100 kDa) from seeds of the legumes Canavalia brasiliensis (CnBr), Cratylia floribunda (CFL), Phaseolus vulgaris (PHA) and Vatairea macrocarpa (VML), temporarily stimulate the respiration of Rhizobium tropici-CIAT899 and R. etli-CFN42. These stimulants were significant (P < 0.05) in bacterial suspensions (> 2.85 mg dry biomass ml–1), having at least 6200 molecules of lectins per bacteria. The VML (20 g ml–1), induced specific O2 demand of 2.3–2.5 M O2 min–1 mg dry biomass–1, in CFN42 and CIAT899, respectively. However, CnBr, CFL and PHA induced smaller demands of O2 (5×), in both strains. The order of affinities of the lectins was approximately VML > PHA > CFL > CnBr, with regard to respiratory stimuli in CIAT899 strain. The co-administration of 10 g VML ml–1 and 9.8 M galactose, in CIAT899 suspensions, reduced the respiratory stimuli significantly in relation to the treatment with VML alone. These respiratory stimuli, induced by the lectins, increase the significance of the interaction lectin × Rhizobium in terms of bacterial physiology. Its understanding could be important in relation to bacterial symbiotic behaviour.  相似文献   

6.
H2-oxidizing CO2-reducing acetogenic bacteria were isolated from gut contents of Nasutitermes nigriceps termites. Isolates were strictly anaerobic, Gram negative, endospore-forming, straight to slightly curved rods (0.5–0.8×2–8 m) that were motile by means of lateral flagella. Cells were oxidase negative, but catalase positive and possessed a b-type cytochrome(s) associated with the cell membrane. Cells grew anaerobically with H2+CO2 as energy source and catalyzed a total synthesis of acetate from this gas mixture. H2 uptake by a representative isolate (strain JSN-2) displayed a K m=6 M and V max=380 nmol x min-1 x mg protein-1. Other substrates used as energy sources for growth and acetogenesis included CO, methanol, betaine, trimethoxybenzoate, and various other organic acids. Succinate was also fermented, but propionate was formed from this substrate instead of acetate. Of a variety of sugars and sugar alcohols tested, only mannitol supported growth. Cells grew optimally at 30° C and pH 7.2 and required yeast extract or a source of amino acids (e.g. Casamino acids) for good growth. During initial enrichment and isolation, cells appeared sensitive to various reducing agents commonly employed in media for anaerobes. The DNA base composition of strain JSN-2 was 48.6 mol% G+C. On the bases of cell morphology, substrate utilization spectrum, and DNA base composition, strain JSN-2 is here-with proposed as the type strain of the new species Sporomusa termitida.Journal article no. 12513 from the Michigan Agricultural Experiment Station  相似文献   

7.
Malic enzyme of the phototrophic bacterium Chromatium vinosum strain D that lacks malate dehydrogenase was partially purified yielding a specific activity of 55 units/mg protein. The constitutive enzyme with a molecular weight of 110,000 and a pH optimum of 8.0 was absolutely dependent on the presence of a monovalent cation (NH 4 + , K+, Cs+, or Rb+) as well as a divalent cation (Mn2+, or Mg2+). The enzyme was inhibited by oxaloacetate, glyoxylate, and NADPH. The K 0.5 value for L-malate and the inhibition constants for oxaloacetate and glyoxylate are dependent on the concentration of the monovalent cation, whereas the K m value for NADP (18 M) and the K 1 value for NADPH (42 M) are independent. Throughout all kinetic measurements hyperbolic saturation curves and linear double reciprocal plots were obtained.Abbreviations OAA oxaloacetate - OD optical density  相似文献   

8.
The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al3+ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]mono. In solutions with similar [Al]mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.  相似文献   

9.
1. 125I-Endothelin (ET)-1 binding to the rat anterior pituitary gland was saturable and single, with a K d of 71 pM and a B max of 120 fmol/mg.2. When 1.0 M BQ-123 (ETA antagonist) was added to the incubation buffer, the binding parameters were 8.3 pM and 8.0 fmol/mg, whereas 10 nM sarafotoxin S6c (ETBagonist) exerted little change in these binding parameters (K d,72pM;B max, 110 fmol/mg).3. ETB receptor-related compounds such as sarafotoxin S6c, ET-3, IRL1620, and BQ-788 competitively inhibited 125I-ET-1 binding, only when 1.0 M BQ-123 was present in the incubation buffer.4. Thus, the ETB receptor is capable of binding ET-1 when the ETA receptor is being occupied by BQ-123. A collaboration mechanism between the ETA and the ETB receptor may function in the recognition of ET-1, a typical bivalent ligand.  相似文献   

10.
Cell suspension cultures of Taxus chinensis, supplemented with 25 g sucrose l–1, produced 11 mg cephalomanine l–1, 21 g biomass l–1 and 19 nkat geranylgeranyl diphosphate (GGPP) synthase activity g protein–1. Supplementation of the cultures with 100 M methyl jasmonate (MJA) produced 17 mg cephalomanine l–1, 6 g biomass l–1 and 78 nkat GGPP synthase activity g protein–1. Addition of sucrose and MJA together produced 24 mg cephalomanine l–1, 18 g biomass l–1 and 55 nkat GGPP synthase activity g protein–1.  相似文献   

11.
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 13CCO 2 = –50.2 ± 0.4, 13Cbiom = –46.6 ± 0.4, and 13Cexo = –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 13CCO 2 = –24.1 ± 0.4, 13Cbiom = –19.2 ± 0.4, and 13Cexo = –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.  相似文献   

12.
The distribution of labile Cd and Zn in two contrasting soils was investigated using isotopic exchange techniques and chemical extraction procedures. A sewage sludge amended soil from Great Billings (Northampton, UK) and an unamended soil of the Countesswells Association obtained locally (Aberdeen, UK) were used. 114Cd and 67Zn isotopes were added to a water suspension of each soil and the labile metal pool (E-value) determined from the isotope dilution. Samples were obtained at 13 time points from 1h to 50 days. For the sewage sludge amended soil, 29 g Cd g–1 (86% of total) and 806 g Zn g–1 (65% of total) were labile and for the Countesswells soil the value was 8.6 g Zn g–1 (13% of total); limits of detection prevented a Cd E-value from being measured in this soil. The size of the labile metal pool was also measured by growing plants for 90 days and determining the isotopic content of the plant tissue (L-value). Thlaspi caerulescensJ. & C. Presl (alpine penny cress), a hyperaccumulator of Zn and Cd, Taraxacum officinale Weber (dandelion) and Hordeum vulgare L. (spring barley) were used. L-values were similar across species and lower than the E-values. On average the L-values were 23±0.8 g Cd g–1 and 725±14 g Zn g–1 for the Great Billings soil and 0.29±0.16 g Cd g–1 and 7.3±0.3 g Zn g–1 for the Countesswells soil. The extractable metal content of the soils was also quantified by extraction using 0.1 M NaNO3, 0.01 M CaCl2, 0.5 M NaOH, 0.43 M CH3COOH and 0.05 M EDTA at pH 7.0. Between 1.3 and 68% of the total Cd and between 1 and 50% of the total Zn in the Great Billings soil was extracted by these chemicals. For the Countesswells soil, between 6 and 83% of the total Cd and between 0.1 and 7% of the total Zn was extracted. 0.05 M EDTA and 0.43 M CH3COOH yielded the greatest concentrations for both soils but these were less than the isotopic estimates. On the whole, E-values were numerically closer to the L-values than the chemical extraction values. The use of isotopic exchange provides an alternative estimate of the labile metal pool within soils compared to existing chemical extraction procedures. No evidence was obtained that T. caerulescens is able to access metal within the soil not freely available to the other plants species. This has implications for long term remediation strategies using hyperaccumulating plant species, which are unlikely to have any impact on non-labile Cd and Zn in contaminated soil.  相似文献   

13.
Twenty-seven species of common seaweeds from the coast of Korea havebeen screened for antifouling activity. The seaweed extracts were tested inlaboratory assays against the marine fouling green alga Enteromorphaprolifera and the blue mussel Mytilus edulis. Tissue growth, sporesettlement, zygote formation and germlings of the E. prolifera wereinhibited by methanol extracts of the seaweed Ishige sinicola (= I. foliacea) and Sargassum horneri. Spore settlement was stronglyinhibited by using extract concentrations as low as 30 g mL-1with I. sinicola and 120 g mL-1 with S. horneri. The repulsive activity of the foot of the mussel was completely inhibited bymethanol extracts of I. sinicola and Scytosiphon lomentaria atconcentrations of 40 g per 10 L drop supplied to eachmussel. These extracts also showed strong antifouling activities onlarval settlement with, respectively, no or only 6% of the spat settlingwhen a test concentration of 0.8 mg mL-1 was used. This work isthe first stage towards the development of novel antifouling agents frommarine macroalgae.  相似文献   

14.
Summary From acetylene reduction assays over a 10-month period starting in April 1979, nodule activities averaged 18.78 (se 4.67) moles C2H4 g nodule dw–1 h–1 forAlnus rubra and 59.95 (se 12.14) moles C2H4 g nodule dw–1 h–1 forCytisus scorparius. Plant rates were 1.91 (se. 47) moles C2H4 plant–1 h–1 forA. rubra and 0.55 (se. 17) moles C2H4 plant–1 h–1 forC. Scoparius. Plant activity and total leaf N were strongly correlated with the dw of other plant parts, but nodule activity and percent leaf N were not. Plant and nodule activities were not associated with temperature, moisture stress, precipitation events or percent light for either species over the growing season nor for 54A. rubra sampled in mid-season 1979 on one replication. After 5 to 6 growing seasons, 14A. rubra on the same site ranged from 30 to 332 cm in height and showed strong correlation between nodule dw, leaf dw, plant size and total leaf N. Results from this study and others indicate logistic equations may be modified to predict the effect of adding a N2 fixing plant to a population of non N2 fixing trees.  相似文献   

15.
The pathway of autotrophic CO2 fixation in Methanobacterium thermoautotrophicum has been investigated by long term labelling of the organism with isotopic acetate and pyruvate while exponentially growing on H2 plus CO2. Maximally 2% of the cell carbon were derived from exogeneous tracer, 98% were synthesized from CO2. Since growth was obviously autotrophic the labelled compounds functioned as tracers of the cellular acetyl CoA and pyruvate pool during cell carbon synthesis from CO2. M. thermoautotrophicum growing in presence of U-14C acetate incorporated 14C into cell compounds derived from acetyl CoA (N-acetyl groups) as well as into compounds derived from pyruvate (alanine), oxaloacetate (aspartate), -ketoglutarate (glutamate), hexosephosphates (galactosamine), and pentosephosphates (ribose). The specific radioactities of N-acetylgroups and of the three amino acids were identical. The hexosamine exhibited a two times higher specific radioactivity, and the pentose a 1.6 times higher specific radioactivity than e.g. alanine. M. thermoautotrophicum growing in presence of 3-14C pyruvate, however, did not incorporate 14C into cell compounds directly derived from acetyl CoA. Those compounds derived from pyruvate, dicarboxylic acids and hexosephosphates became labelled. The specific radioactivities of alanine, aspartate and glutamate were identical; the hexosamine had a specific radioactivity twice as high as e.g. alanine.The finding that pyruvate was not incorporated into compounds derived from acetyl CoA, whereas acetate was incorporated into derivatives of acetyl CoA and pyruvate in a 1:1 ratio demonstrates that pyruvate is synthesized by reductive carboxylation of acetyl CoA. The data further provide evidence that in this autotrophic CO2 fixation pathway hexosephosphates and pentosephosphates are synthesized from CO2 via acetyl CoA and pyruvate.  相似文献   

16.
Husen  Jia  Dequan  Li 《Photosynthetica》2002,40(1):139-144
The responses to irradiance of photosynthetic CO2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd). Net photosynthetic rate (P N) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (mol m-2 s-1, while the PS2 non-cyclic electron transport (P-rate) showed a maximum at PPFD 800 mol m-2 s-1. With PPFD increasing, either leaf potential photosynthetic CO2 assimilation activity (Fd/Fs) and PS2 maximal photochemical activity (Fv/Fm) decreased or the ratio of the inactive PS2 reaction centres (RC) [(Fi – Fo)/(Fm – Fo)] and the slow relaxing non-photochemical Chl fluorescence quenching (qs) increased from PPFD 1 200 mol m-2 s-1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(Fs – Fo)/Fm – Fo)], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (qf and qm) increased remarkably from PPFD 900 (mol m-2 s-1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 mol m-2 s-1 and photoinhibition occurred above PPFD 900 mol m-2 s-1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 mol m-2 s-1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 mol m-2 s-1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter P N and the Chl fluorescence parameter Fv/Fm as a definition of saturation irradiance and photoinhibition of plant leaves.  相似文献   

17.
Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l–1, = 49.0 ag l–1. Well water samples generally contained less than 10 g l–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l–1) and many samples exceeded the maximum permissible limit (50 g l–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g–1 ), X = 0.7 g g–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.  相似文献   

18.
The aluminium (Al) tolerance of 34 temperate legume species (143 genotypes, including 57 from Trifolium repens) was determined in 60 experiments over a 3 year period in a low ionic strength (2.7 × 10-3 M) solution culture. For each genotype, the relationship between solution Al3+ activity (M) and relative yield was determined and the Al3+ activity associated with a 50% reduction in yield (AlRY50) calculated. In addition, plant chemical concentrations were determined in at least one genotype from most species. For white clover, AlRY50 over all genotypes had an approximately normal distribution with mean of 1.31 M for the tops and 1.51 M for the roots, and a standard deviation of about 0.4. This suggested that Al tolerance had a polygenic inheritance. For the other species tested, AlRY50 ranged from 0.15 to 4.53 M in the tops and from 0.21 to 4.89 M in the roots. In the tops and roots, 37% and 26% respectively of the genotypes had an AlRY50 less than 1 M, including all species tested in the genera Melilotus and Medicago. Only 8% or 23% of the genotypes, based on the tops and roots respectively, had an AlRY50 greater than 2, including all genotypes in the species Lotus pedunculatus. Except for Lotus, there were no consistent differences between genera in plant chemical concentrations. In Lotus, concentrations of Ca, Zn, Mn and Cu in the tops and of all elements except B in the roots were lower than that of the other species. The AlRY50 of the species was not related to plant chemical concentrations in the absence of Al. Depending on the plant element, increasing solution Al concentrations had no significant effect on plant chemical concentrations for 56–94% of the species. When a significant effect did occur, increasing Al in solution generally decreased S and K concentrations and increased Mn, Zn, Cu Fe, B and Al concentrations in the tops and roots and decreased Ca concentrations in the tops. Plant P concentrations decreased in the tops but increased in the roots. Increasing Al in solution increase plant Al at the average rate of 44 g g-1 M -1 (range 20–87) in the tops and 333 g M -1 (range 162–616) in the roots.  相似文献   

19.
Iron-efficient (WF9 corn and Coker 227 oat) and Fe-inefficient (ys1 corn and TAM 0–312 oat) cultivars were comparatively tested for their response to Fe-deficiency stress induced by the use of either ferrous or ferric chelators. Corn and oats were grown in 20 M Fe with 0, 60, and 120 M BPDS and 40 M Fe with 0, 120, and 240 M BPDS and 20 M Fe with 0 and 40 M EDDHA. All four cultivars tested, both Fe-efficient and Fe-inefficient, continuously reduced Fe3+ to Fe2+ at a low level as evidenced by the production of Fe2+ (BPDS)3 in test nutrient solutions over time. Severity of chlorosis increased as more BPDS was added to the nutrient solutions for both WF9 and ys1 corn, but unlike corn, Coker 227 and TAM 0-312 oats were both able to obtain Fe from the Fe2+ (BPDS)3 complex and were less chlorotic as a result. In short-term (4-hour) in vivo measurements, iron-stressed WF9 (Fe-efficient) corn reduced more Fe3+ to Fe2+ than similarly stressed ys1 corn, Coker 227 oat or TAM 0-312 oat. Thus, at the same time that Fe-efficient WF9 corn reduces more Fe than the other cultivars, it is also unable to compete with BPDS for that Fe in the nutrient solution. These differences coupled with the observation that only Coker 227 oat produced measureable iron solubilizing substances (phytosiderophores) suggest that these two species differ in their mechanisms for obtaining Fe during Fe-deficiency stress.  相似文献   

20.
The marine green sulfur bacterium Chlorobium vibrioforme strain 1930 produced H2 and elemental sulfur from sulfide or thiosulfate under N limitation in the light. H2 production depended on nitrogenase and occurred only in the absence of ammonia. Methionine sulfoximine, an inhibitor of glutamine synthetase, prevented the switch-off by ammonia. In defined syntrophic cocultures of the acetate-oxidizing, sulfur-reducing bacterium Desulfuromonas acetoxidans with green sulfur bacteria, H2 was produced from acetate via a light-driven sulfur cycle. The sulfur-reducing bacterium could not be replaced by sulfate-reducing bacteria in these experiments. In a coculture of the marine Chlorobium vibrioforme strain 1930 and the sulfur-reducing bacterium Desulfuromonas acetoxidans strain 5071, optimum long-term H2 production from acetate was obtained with molecular nitrogen as N source, at low light intensity (110 mol · m-2 · s-1), in sulfide-reduced mineral medium (2 mM Na2S) at pH 6.8. Traces of sulfide (10 M) were sufficient to keep the sulfur cycle running. The coculture formed no poly--hydroxyalkanoates (PHA), but 20%–40% polysaccharide per cell dry mass. Per mol acetate added, the coculture formed 3.1 mol of H2 (78% of the theoretical maximum). Only 8% of the reducing equivalents was incorporated into biomass. The maximum rate of H2 production was 1300 ml H2 per day and g cell dry mass.Non-standard abbrevations MOPS 2-(N-morpholino) propane sulfonic acid - MSX Methionine sulfoximine - PHA poly--hydroxyalkanoates  相似文献   

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