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1.
Résumé La possibilité de photoproduire de l'hydrogène à partir de soufre et de sulfure par des Chromatiaceae appartenant aux genres Chromatium, Thiocapsa, Thiocystis et Ectothiorhodospira a été examiniée. Sur huit souches testées, six seulement libèrent de l'hydrogène en présence de sulfure. Sur soufre, les Ectothiorhodospira forment du H2 alors que les autres souches excrétent du sulfure. Des expériences manométriques avec une souche d'Ectothiorhodospira montrent que la photoproduction de H2 est étroitement corrélée à l'assimilation du CO2 et que l'utilisation des substrats endogènes est exacerbée par le sulfure.
Photoproduction of hydrogen from sulfur and sulfide by chromatiaceae
H2 photoevolution from sulfur and sulfide by Chromatiaceae belonging to the genera Chromatium, Thiocapsa, Thiocystis and Ectothiorhodospira has been investigated. In the presence of sulfide, six of the eight strains studied evolve hydrogen. With sulfur, Ectothiorhodospira produce H2 but the other strains excrete sulfide. Manometric experiments show a correlation between H2 evolution and CO2 assimilation and an increase of endogenous substrate utilization with sulfide in Ectothiorhodospira.相似文献
2.
Seventeen strains of phototrophic bacteria (4 strains of Chromatium spp., 2 strains of Thiocapsa sp., 4 strains of Ectothiorhodospira spp., 2 strains of Rhodopseudomonas sp., and 5 strains of Chlorobium spp.) have been grown in sulfide-limited continuous cultures to assess the affinity for sulfide. It was found that the affinity (calculated as the initial slope of the specific growth rate versus the concentration of sulfide) is higher in those phototrophic bacteria that deposit elemental sulfur outside the cells, than in those bacteria that store the sulfur inside the cells. A hypothesis is presented to explain this correlation.Dedicated to Prof. Dr. Hans G. Schlegel on the occasion of his 60th birthday 相似文献
3.
A novel type of purple sulfur bacterium was isolated from a hypersaline sulfur spring on the shore of the Dead Sea. The cells of the isolate are irregularly rod-shaped or curved, and motile by means of a tuft of polar flagella. The photosynthetic system, containing bacteriochlorophyll a and carotenoids of the spirilloxanthin series, is located on stacks of lamellar membranes in the cell cytoplasm. The organism can grow either photoautotrophically with sulfide as electron donor, which is oxidized via extracellular sulfur to sulfate, or photoheterotrophically, using acetate, succinate, fumarate, malate or pyruvate as carbon sources. The bacterium is obligately anaerobic, and requires a source of reduced sulfur for growth. The isolate is moderately halophilic, and grows optimally at NaCl concentrations between 3 and 8%, temperatures between 30 and 45°C, and neutral pH. 16S ribosomal RNA oligonucleotide cataloging suggests a close relationship to purple sulfur bacteria of the genus Ectothiorhodospira. As the isolate differs greatly from the described members of the genus Ectothiorhodospira, we describe the isolate as a new species, and propose the name Ectothiorhodospira marismortui sp. nov. 相似文献
4.
The sulfate-reducing bacteriumDesulfobulbus propionicus oxidized sulfide, elemental sulfur, and sulfite to sulfate with oxygen as electron acceptor. Thiosulfate was reduced and
disproportionated exclusively under anoxic conditions. When small pulses of oxygen were added to washed cells in sulfide-containing
assays, up to 3 sulfide molecules per O2 disappeared transiently. After complete oxygen consumption, part of the sulfide reappeared. The intermediate formed was identified
as elemental sulfur by chemical analysis and turbidity measurements. When excess sulfide was present, sulfur dissolved as
polysulfide. This process was faster in the presence of cells than in their absence. The formation of sulfide after complete
oxygen consumption was due to a disproportionation of elemental sulfur (or polysulfide) to sulfide and sulfate. The uncoupler
tetrachlorosalicylanilide (TCS) and the electron transport inhibitor myxothiazol inhibited sulfide oxidation to sulfate and
caused accumulation of sulfur. In the presence of the electron transport inhibitor 2-n-heptyl-4-hydroxyquinoline-N-oxide (HQNO), sulfite and thiosulfate were formed. During sulfur oxidation at low oxygen concentrations, intermediary formation
of sulfide was observed, indicating disproportionation of sulfur also under these conditions. It is concluded that sulfide
oxidation inD. propionicus proceeds via oxidation to elemental sulfur, followed by sulfur disproportionation to sulfide and sulfate.
Dedicated to Prof. Dr. Dr. h.c. Norbert Pfennig on the occasion of his 70th birthday 相似文献
5.
Simone Dannenberg Michael Kroder Waltraud Dilling Heribert Cypionka 《Archives of microbiology》1992,158(2):93-99
All of fourteen sulfate-reducing bacteria tested were able to carry out aerobic respiration with at least one of the following electron donors: H2, lactate, pyruvate, formate, acetate, butyrate, ethanol, sulfide, thiosulfate, sulfite. Generally, we did not obtain growth with O2 as electron acceptor. The bacteria were microaerophilic, since the respiration rates increased with decreasing O2 concentrations or ceased after repeated O2 additions. The amounts of O2 consumed indicated that the organic substrates were oxidized incompletely to acetate; only Desulfobacter postgatei oxidized acetate with O2 completely to CO2. Many of the strains oxidized sulfite (completely to sulfate) or sulfide (incompletely, except Desulfobulbus propionicus); thiosulfate was oxidized only by strains of Desulfovibrio desulfuricans; trithionate and tetrathionate were not oxidized by any of the strains. With Desulfovibrio desulfuricans CSN and Desulfobulbus propionicus the oxidation of inorganic sulfur compounds was characterized in detail. D. desulfuricans formed sulfate during oxidation of sulfite, thiosulfate or elemental sulfur prepared from polysulfide. D. propionicus oxidized sulfite and sulfide to sulfate, and elemental sulfur mainly to thiosulfate. A novel pathway that couples the sulfur and nitrogen cycles was detected: D. desulfuricans and (only with nitrite) D. propionicus were able to completely oxidize sulfide coupled to the reduction of nitrate or nitrite to ammonia. Cell-free extracts of both strains did not oxidize sulfide or thiosulfate, but formed ATP during oxidation of sulfite (37 nmol per 100 nmol sulfite). This, and the effects of AMP, pyrophosphate and molybdate on sulfite oxidation, suggested that sulfate is formed via the (reversed) sulfate activation pathway (involving APS reductase and ATP sulfurylase). Thiosulfate oxidation with O2 probably required a reductive first step, since it was obtained only with energized intact cells.Abbreviations
CCCP
carbonyl cyanide m-chlorophenylhydrazone
-
APS
adenosine phosphosulfate or adenylyl sulfate 相似文献
6.
Ralf Steudel Gabriele Holdt Pieter T. Visscher Hans van Gemerden 《Archives of microbiology》1990,153(5):432-437
Cultures of Chromatium vinosum, devoid of sulfur globules, were supplemented with sulfide and incubated under anoxic conditions in the light. The concentrations of sulfide, polysulfides, thiosulfate, polythionates and elemental sulfur (sulfur rings) were monitored for 3 days by ion-chromatography and reversed-phase HPLC. While sulfide disappeared rapidly, thiosulfate and elemental sulfur (S6, S7 S8 rings) were formed. After sulfide depletion, the concentration of thiosulfate decreased fairly rapidly, but elemental sulfur was oxidized very slowly to sulfate. Neither polysulfides (S
x
2–
), polythionates (SnO
6
2–
, n=4–6), nor other polysulfur compounds could be detected, which is in accordance with the fact that sulfide-grown cells were able to oxidize polysulfide without lag. The nature of the intracellular sulfur globules is discussed. 相似文献
7.
Johannes F. Imhoff Brian J. Tindall William D. Grant Hans G. Trüper 《Archives of microbiology》1981,130(3):238-242
A new phototrophic bacterium was isolated from Jordanian and Kenyan alkaline salt lakes. Cells are rod shaped, 1.5 m wide and 2–4 m long, and motile by polar flagella. They divide by binary fission, and possess photosynthetic membranes as lamellar stacks similar to those in the other species of the genus Ectothiorhodospira and the brown colored Rhodospirillum species. The presence of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series is indicated by the absorption spectra of living cells. Under certain growth conditions the cells form gas vacuoles, may become immotile and float to the top of the culture medium. Sulfide and thiosulfate are used as photosynthetic electron donors. During the oxidation of sulfide to sulfate, elemental sulfur is formed, which is accumulated outside the cells. The organisms are strictly anaerobic, do not require vitamins, are moderately halophilic and need alkaline pH-values for growth. The new species Ectothiorhodospira vacuolata is proposed. 相似文献
8.
Sigurlaug Skirnisdottir Gudmundur O. Hreggvidsson Olle Holst Jakob K. Kristjansson 《Microbiological research》2001,156(1):41
Thermophilic bacteria were isolated from a sulfide-rich, neutral hot spring in Iceland on gelrite minimal medium with 16 mM thiosulfate. The isolates were aerobic, obligate chemolithoautotrophs and used thiosulfate and sulfur as electron donors, producing sulfate from both substrates. No growth was observed with hydrogen as the sole electron donor, and no hydrogenase activity was detected. The cells were gram-negative and usually single, 4—5 μm long and 0.7 μm in diameter and formed sulfur globules after a few days of incubation. By SSU rRNA sequence comparisons, the bacterium was placed in the genus Hydrogenobacter with the closest relative to be Calderobacterium hydrogenophilum with 98.3% sequence similarity. This novel bacterium shows an ecological adaptation to high sulfide springs and is differentiated from its closest known relatives by lack of H2 oxidation, deposition of sulfur and lower growth temperature. 相似文献
9.
Cytochromes c
3 of different strains of sulfatereducing bacteria have been purified and tested for their capacity to reduce colloidal sulfur to hydrogen sulfide. The results are in good agreement with the activities reported for the whole cells. Cytochrome c
3 is the sulfur reductase of some strains of sulfate-reducing bacteria such as Desulfovibrio desulfuricans Norway 4 and sulfate-reducing bacterium strain 9974 from which the sulfur reductase activity can be purified with the cytochrome c
3. In contrast, Desulfovibrio vulgaris Hildenborough cytochrome c
3 is inhibited by the product of the reaction namely hydrogen sulfide. Chloramphenicol has no effect on the sulfur reductase activity of D. desulfuricans Norway 4 when resting cells grown on lactate-sulfate medium are put in the presence of colloidal sulfur. This shows that the sulfur reductase activity is constitutive and corresponds to the fact that colloidal sulfur grown cells do not contain more cytochrome c
3 (or another sulfur reductase) than lactate-sulfate-grown cells. 相似文献
10.
A detailed analysis of the periplasmic electron carriers of the photosynthetic bacterium Ectothiorhodospira sp. has been performed. Two low mid-point redox potential electron carriers, cytochrome c′ and cytochrome c, are detected. A high potential iron–sulfur protein is the only high mid-point redox potential electron transfer component
present in the periplasm. Analysis of light-induced absorption changes shows that this high potential iron–sulfur protein
acts in vivo as efficient electron donor to the photo-oxidized high potential heme of the Ectothiorhodospira sp. reaction center.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
Isolation and Characterization of Strains CVO and FWKO B, Two Novel Nitrate-Reducing, Sulfide-Oxidizing Bacteria Isolated from Oil Field Brine 总被引:9,自引:4,他引:5
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Diane Gevertz Anita J. Telang Gerrit Voordouw Gary E. Jenneman 《Applied microbiology》2000,66(6):2491-2501
Bacterial strains CVO and FWKO B were isolated from produced brine at the Coleville oil field in Saskatchewan, Canada. Both strains are obligate chemolithotrophs, with hydrogen, formate, and sulfide serving as the only known energy sources for FWKO B, whereas sulfide and elemental sulfur are the only known electron donors for CVO. Neither strain uses thiosulfate as an energy source. Both strains are microaerophiles (1% O2). In addition, CVO grows by denitrification of nitrate or nitrite whereas FWKO B reduces nitrate only to nitrite. Elemental sulfur is the sole product of sulfide oxidation by FWKO B, while CVO produces either elemental sulfur or sulfate, depending on the initial concentration of sulfide. Both strains are capable of growth under strictly autotrophic conditions, but CVO uses acetate as well as CO2 as its sole carbon source. Neither strain reduces sulfate; however, FWKO B reduces sulfur and displays chemolithoautotrophic growth in the presence of elemental sulfur, hydrogen, and CO2. Both strains grow at temperatures between 5 and 40°C. CVO is capable of growth at NaCl concentrations as high as 7%. The present 16s rRNA analysis suggests that both strains are members of the epsilon subdivision of the division Proteobacteria, with CVO most closely related to Thiomicrospira denitrifcans and FWKO B most closely related to members of the genus Arcobacter. The isolation of these two novel chemolithotrophic sulfur bacteria from oil field brine suggests the presence of a subterranean sulfur cycle driven entirely by hydrogen, carbon dioxide, and nitrate. 相似文献
12.
Ben -Li Liu Arnold J. Hoff Lian -Quan Gu Liang -Bi Li Pei -Zhen Zhou 《Photosynthesis research》1991,30(2-3):95-106
The relationship between the structure of reconstituted plastoquinone derivatives and their ability to recover the Hill reaction was investigated by extraction and reconstitution of lyophilized chloroplasts from spinach, followed by monitoring DCIP photoreduction at 600 nm. The results show that: It is not essential that the plastoquinone side chain be an isoprenoid or a phytol; the activity increases with increasing length of the side chain up to 13–15 carbon atoms; for chains longer than 15 carbon atoms, the activity is practically constant. Lipophilic groups (such as -Br) in the side chain increased the activity, hydrophilic groups (such as -OH) decreased the activity. Conjugated double bonds in the side chain decreased the activity greatly, but non-conjugated double bonds had almost no effect on the activity, indicating a requirement of flexibility of the side chain. The activity is decreased in the order of PQ, UbiQ and MQ, showing a large effect of the ring structure.Abbreviations DCIP
2,6-dichlorophenolindophenol
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- QA
primary electron acceptor in PS II reaction centers
- QB
secondary electron acceptor in PS II reaction centers
- PQ
n
plastoquinones with an isoprenoid side chain (n, number of the isoprenoid units in the side chain)
- PQ-n
synthetic plastoquinones with alkyl side chain (n, number of the carbon atoms in the alkyl side chain)
- PQ-n
synthetic plastoquinones with a double bond in the alkyl side chain
- UQ
n
ubiquinones with an isoprenoid side chain (n, number of the isoprenoid units in the side chain)
- UQ-n
synthetic ubiquinones with alkyl side chain (n, number of the carbon atoms in the akyl side chain)
- MQ-n
2-alkyl-1,4-naphthoquinone (n, number of the carbon atoms in the alkyl side chain) 相似文献
13.
DNA-DNA hybridization reveals low DNA homologies (about 14%) between the species of Ectothiorhodospira genus and indicate clearly that the degree of divergence within this genus exceeds the interspecific level. The degree of genome similarities of E. mobilis and E. vacuolata (more than 80% homology) is high and characteristic for the strains of one and the same species.The results of rRNA-DNA and secondary DNA-DNA hybridization indicate the following: Ectothiorhodospira and Thiocapsa are far less related than the genera of one and the same family; the genus Ectothiorhodospira is equidistant from both families of purple sulfur and nonsulfur bacteria. Thus Ectothiorhodospira is a taxon of a higher rank than a genus; we agree with Imhoff's proposal of a new family Ectothiorhodospiraceae. 相似文献
14.
Sequences of the 16S rRNA gene were determined from all type strains of the recognized Ectothiorhodospira species and from a number of additional strains. For the first time, these data resolve the phylogenetic relationships of
the Ectothiorhodospiraceae in detail, confirm the established species, and improve the classification of strains of uncertain
affiliation. Two major groups that are recognized as separate genera were clearly established. The extremely halophilic species
were removed from the genus Ectothiorhodospira and reassigned to the new genus Halorhodospira gen. nov., to recognize that the most halophilic eubacteria are species of this genus. These species are Halorhodospira halophila comb. nov., Halorhodospira halochloris comb. nov., and Halorhodospira abdelmalekii comb. nov. Among the slightly halophilic Ectothiorhodospira species, the classification of strains belonging to Ectothiorhodospira mobilis and Ectothiorhodospira shaposhnikovii was improved. Several strains that were tentatively identified as Ectothiorhodospira mobilis form a separate cluster on the basis of their 16S rDNA sequences and are recognized as two new species: Ectothiorhodospira haloalkaliphila sp. nov., which includes the most alkaliphilic strains originating from strongly alkaline soda lakes, and Ectothiorhodospira marina, describing isolates from the marine environment.
Received: 12 October 1995 / Accepted: 1 December 1995 相似文献
15.
Jasmine S. Berg Anne Schwedt Anne-Christin Kreutzmann Marcel M. M. Kuypers Jana Milucka 《Applied and environmental microbiology》2014,80(2):629-636
Zero-valent sulfur is a key intermediate in the microbial oxidation of sulfide to sulfate. Many sulfide-oxidizing bacteria produce and store large amounts of sulfur intra- or extracellularly. It is still not understood how the stored sulfur is metabolized, as the most stable form of S0 under standard biological conditions, orthorhombic α-sulfur, is most likely inaccessible to bacterial enzymes. Here we analyzed the speciation of sulfur in single cells of living sulfide-oxidizing bacteria via Raman spectroscopy. Our results showed that under various ecological and physiological conditions, all three investigated Beggiatoa strains stored sulfur as a combination of cyclooctasulfur (S8) and inorganic polysulfides (Sn2−). Linear sulfur chains were detected during both the oxidation and reduction of stored sulfur, suggesting that Sn2− species represent a universal pool of bioavailable sulfur. Formation of polysulfides due to the cleavage of sulfur rings could occur biologically by thiol-containing enzymes or chemically by the strong nucleophile HS− as Beggiatoa migrates vertically between oxic and sulfidic zones in the environment. Most Beggiatoa spp. thus far studied can oxidize sulfur further to sulfate. Our results suggest that the ratio of produced sulfur and sulfate varies depending on the sulfide flux. Almost all of the sulfide was oxidized directly to sulfate under low-sulfide-flux conditions, whereas only 50% was oxidized to sulfate under high-sulfide-flux conditions leading to S0 deposition. With Raman spectroscopy we could show that sulfate accumulated in Beggiatoa filaments, reaching intracellular concentrations of 0.72 to 1.73 M. 相似文献
16.
Hano N Nakashima Y Shinzawa-Itoh K Yoshikawa S 《Journal of bioenergetics and biomembranes》2003,35(3):257-265
Steady state kinetics of bovine heart NADH: coenzyme Q oxidoreductase using coenzyme Q with two isoprenoid unit (Q2) or with a decyl group (DQ) show an ordered sequential mechanism in which the order of substrate binding and product release is NADH-Q2 (DQ) -Q2H2 (DQH2)-NAD+ in contrast to the order determined using Q1 (Q1-NADH-NAD+-Q1H2) (Nakashima et al., J. Bioenerg. Biomembr.
34, 11–19, 2002). The effect of the side chain structure of coenzyme Q suggests that NADH binding to the enzyme results in a conformational change, in the coenzyme Q binding site, which enables the site to accept coenzyme Q with a side chain significantly larger than one isoprenoid unit. The side chains of Q2 and DQ bound to the enzyme induce a conformational change in the binding site to stabilize the substrate binding, while the side chain of Q1 (one isoprenoid unit) is too short to induce the conformational change. 相似文献
17.
Sulfide utilization by purple nonsulfur bacteria 总被引:1,自引:0,他引:1
Summary The purple nonsulfur bacteria Rhodospirillum rubrum SMG 107, Rhodopseudomonas capsulata SMG 155, Rps. sphaeroides SMG 158 and Rps. palustris SMG 124 were tested for a possible utilization of sulfide. The first three strains were found to oxidize sulfide to extracellular elemental sulfur only, whereas Rps. palustris SMG 124 converted sulfide into sulfate without intermediate accumulation of elemental sulfur. Growth ceased at lower sulfide concentrations than usually found with purple sulfur bacteria. In consequence of the low sulfide tolerance information on the specific growth rates obtainable with sulfide as photosynthetic electron donor could not be provided by cultivation in batch cultures. Sulfide-limited chemostat cultures of Rps. capsulata SMG 155 showed that the maximum specific growth rate was close to 0.14 h-1 (doubling time 5 h). Sulfide was converted into extracellular elemental sulfur at all dilution rates tested. The maximum specific growth rate of Rps. palustris SMG 124 was found to be much lower (less than 0.03 h-1). Sulfate was the only product of the conversion of sulfide.These data show that at least some purple nonsulfur bacteria may play a role in the dissimilatory sulfur cycle in nature. Taxonomic implications of our results are discussed.Abbreviation SMG
Sammlung für Mikroorganismen, Göttingen 相似文献
18.
Transformation of galena to pyromorphite produces bioavailable sulfur for neutrophilic chemoautotrophy
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The aqueous concentration of lead [Pb(II)] in geochemical environments is controlled by the solubility of Pb‐bearing minerals and their weathering products. In contaminated soils, a common method for in situ stabilization of Pb(II) is the addition of phosphate to convert more redox sensitive sulfide minerals into sparingly soluble pyromorphite [Pb5(PO4)3X]. In this study, we conducted experimental studies to investigate the fate of reduced sulfur during the conversion of galena [PbS] to chloropyromorphite [Pb5(PO4)3Cl]. Powder X‐ray diffraction analysis indicated that the reaction of phosphate with galena under oxic conditions resulted in the oxidation of sulfide and formation of elemental sulfur [S8]. Under oxic abiotic conditions, the S8 was retained in the solid phase, and negligible concentrations of sulfur as sulfide and thiosulfate were detected in the aqueous phase and only a small amount of sulfate. When PbS reacted in the presence of the chemoautotrophic organism Bosea sp. WAO, the S8 in the secondary mineral was oxidized to sulfate. Strain WAO produced significantly more sulfate from the secondary S8 than from the primary galena. Microscopic analysis of mineral–microbe aggregates on mineral‐embedded slide cultures showed that the organism was colocalized and increased in biomass over time on the secondary mineral surface supporting a microbial role. The results of this study indicate that stimulation of sulfur‐oxidizing activity may be a direct consequence of phosphate amendments to Pb(II)‐contaminated soils. 相似文献
19.
Günter A. Peschek 《Archives of microbiology》1978,119(3):313-322
Photosynthesis by Anacystis nidulans was studied in presence of reduced sulfur or nitrogen compounds, or of hydrogen. O2 evolution and CO2 fixation were depressed by sulfide, sulfite, cysteine, thioglycollate, hydroxylamine and hydrazine. Sulfite, cysteine and hydrazine inhibited O2 evolution much more strongly than CO2 fixation, indicating ability to supply electrons for CO2 photoreduction; DCMU suppressed these photoreductions. In contrast, some anoxygenic photosynthetic CO2 fixation insensitive to DCMU was found with sulfide, thiosulfate and hydrogen. Emerson enhancement studies confirmed that sulfite, cysteine and hydrazine acted on photosystem II, while photoreduction supported by sulfide, thiosulfate and hydrogen needed photosystem I only.Sulfite was photooxidized to sulfate, sulfide to elemental sulfur, and thiosulfate to sulfate plus elemental sulfur; the sulfur accumulated inside the cells. Results on the stoichiometries of the photoreductions were consistent with the photooxidation products determined. Inhibitor studies suggested photosynthetic CO2 fixation through the Calvin cycle.While photoreduction by all reductants used was found to be constitutive in Anacystis, the process was stimulated by anaerobic preincubation with the reductants only in the cases of hydrogen and thiosulfate; this adaptation was prevented by chloramphenicol and by O2. Anaerobic photoautotrophic growth of Anacystis was, however, not observed; the increase in dry weight with H2 and thiosulfate was not accompanied by cell multiplication or by an increase in chlorophyll content. Parallel short-term experiments with Chlorella did not reveal any constitutive photoreduction in this eukaryotic alga.Abbreviations CAP
chloramphenicol
- CCCP
carbonyl cyanide m-chlorophenylhydrazone
- DBMIB
dibromothymoquinone
- DCMU
dichlorophenyl dimethyl urea
- DSPD
disalicylidenepropane diamine-(1,3)
- EDAC
1-ethyl-3(3-dimethylaminopropyl-) carbodiimide 相似文献
20.
H. H. Thiele 《Antonie van Leeuwenhoek》1968,34(1):341-349
Thiocapsa floridana strain 1711, andChromatium strains 1611 and 6412 can grow with molecular hydrogen replacing sulfide as the electron donor. Sulfate suffices as the sulfur source. The incorporation of radioactive sulfur from35S-sulfate was measured in growing cells in which molecular hydrogen or acetate was the electron donor. In cells pre-grown in sulfide, the incorporation of radioactivity began slowly after a lag period; in contrast, cells grown in sulfate took up the marker at a faster rate and without a lag. The radioactivity appeared in protein as cysteine and methionine. No elimination of sulfide was detected during growth. Thus, the reduction of sulfate was purely assimilatory. 相似文献