On Light-Induced Photoconversion of B800 Bacteriochlorophylls in the LH2 Antenna of the Purple Sulfur Bacterium Allochromatium vinosum.

The B800-850 LH2 antenna from the photosynthetic purple sulfur bacterium Allochromatium vinosum exhibits an unusual spectral splitting of the B800 absorption band; i.e., two bands are well-resolved at 5 K with maxima at 805 nm (B800R) and 792 nm (B800B). To provide more insight into the nature of the B800 bacteriochlorophyll (BChl) a molecules, high-resolution hole-burning (HB) spectroscopy is employed. Both white light illumination and selective laser excitations into B800R or B800B lead to B800R → B800B phototransformation. Selective excitation into B800B leads to uncorrelated excitation energy transfer (EET) to B800R and subsequent B800R → B800B phototransformation. The B800B → B800R EET time is 0.9 ± 0.1 ps. Excitation at 808.4 nm (into the low-energy side of B800R) shows that the lower limit of B800R → B850 EET is about 2 ps, as the B800R → B800B phototransformation process could contribute to the corresponding zero-phonon hole width. The phototransformation of B800R leads to a ∼ 200 cm-1 average blue-shift of transition energies, i.e., B800R changes into B800B. We argue that it is unlikely that B800-B850 excitonic interactions give rise to a splitting of the B800 band. We propose that the latter is caused by different protein conformations that can lead to both strong or weak hydrogen bond(s) between B800 pigments and the protein scaffolding. Temperature-dependent absorption spectra of B800, which revealed a well-defined isosbestic point, support a two-site model, likely with strongly and weakly hydrogen-bonded B800 BChls. Thus, BChls contributing to B800R and B800B could differ in the position of the proton in the BChl carbonyl-protein hydrogen bond, i.e., proton dynamics along the hydrogen bond may well be the major mechanism of this phototransformation. However, the effective tunneling mass is likely larger than the proton mass.

Arsenic removal in a sulfidogenic fixed-bed column bioreactor.

In the present study, the bioremoval of arsenic from synthetic acidic wastewater containing arsenate (As(5+)) (0.5-20mg/L), ferrous iron (Fe(2+)) (100-200mg/L) and sulfate (2,000 mg/L) was investigated in an ethanol fed (780-1,560 mg/L chemical oxygen demand (COD)) anaerobic up-flow fixed bed column bioreactor at constant hydraulic retention time (HRT) of 9.6h. Arsenic removal efficiency was low and averaged 8% in case iron was not supplemented to the synthetic wastewater. Neutral to slightly alkaline pH and high sulfide concentration in the bioreactor retarded the precipitation of arsenic. Addition of 100mg/L Fe(2+) increased arsenic removal efficiency to 63%. Further increase of influent Fe(2+) concentration to 200mg/L improved arsenic removal to 85%. Decrease of influent COD concentration to its half, 780 mg/L, resulted in further increase of As removal to 96% when Fe(2+) and As(5+) concentrations remained at 200mg/L and 20mg/L, respectively. As a result of the sulfidogenic activity in the bioreactor the effluent pH and alkalinity concentration averaged 7.4 ± 0.2 and 1,736 ± 239 mg CaCO3/L respectively. Electron flow from ethanol to sulfate averaged 72 ± 10%. X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the nature of the precipitate generated by sulfate reducing bacteria (SRB) activity. Precipitation of arsenic in the form of As2S3 (orpiment) and co-precipitation with ferrous sulfide (FeS), pyrite (FeS2) or arsenopyrite (FeAsS) were the main arsenic removal mechanisms.

Kinetic properties of adenosine triphosphate sulfurylase of intestinal sulfate-reducing bacteria.

The investigation of specific activity of ATP sulfurylase and kinetic properties of the enzyme in cell-free extracts of intestinal bacterial strains Desulfovibrio piger Vib-7 and Desulfomicrobium sp. Rod-9 is presented. The microbiological, biochemical, biophysical and statistical methods were used in the work. The optimal temperature (35°C) and pH 8.0-8.5 for enzyme reaction were determined. An analysis of kinetic properties of ATP sulfurylase has been carried out. Initial (instantaneous) reaction velocity (V0), maximum amount of the product of reaction (Pmax), the reaction time (half saturation period, τ) and maximum velocity of the ATP sulfurylase reaction (Vmax) have been defined. Michaelis constants (Km(Sulfate), Km(ATP), Km(APS), and Km(Pyrophosphate)) of the enzyme reaction were demonstrated for both D. piger Vib-7 and Desulfomicrobium sp. Rod-9 intestinal bacterial strains.

Metal precipitation in an ethanol-fed, fixed-bed sulphate-reducing bioreactor.

A batch upflow fixed-bed sulphate-reducing bioreactor has been set up and monitored for the treatment of synthetic solutions containing divalent iron (100mg/L and 200mg/L), zinc (100mg/L and 200mg/L), copper (100mg/L and 200mg/L), nickel (100mg/L and 200mg/L) and sulphate (1700 mg/L and 2130 mg/L) at initial pH 3-3.5, using ethanol as the sole electron donor. The reactor has been operated at the theoretical stoichiometric ethanol/sulphate ratio. Complete oxidation of ethanol has been achieved through complete oxidation of the intermediately, microbially produced acetate. This is mainly attributed to the presence of Desulfobacter postgatei species which dominated the sulphate-reducing community in the reactor. The reduction of sulphate was limited to about 85%. Quantitative precipitation of the soluble metal ions has been achieved. XRD and SEM-EDS analyses performed on samples of the produced sludge showed poorly crystalline phases of marcasite, covellite and wurtzite as well as several mixed metal sulphides.

[Biosorption properties of extracellular polymeric substances produced by sulfate-reducing bacteria towards Cu(II) ion].

The purpose of the present study was to investigate the Cu2+ biosorption properties of extracellular polymeric substances (EPS) produced by sulfate-reducing bacteria. The composition and physicochemical characteristics of EPS were determined. The adsorption characteristics of EPS towards Cu2+ were examined using thermodynamic equilibrium equations and determined by FTIR and SEM-EDS. The EPS was shown to have a strong copper-binding capacity and the biosorption data obtained were well described by the Freundlich isotherm model. The results of FTIR spectra and SEM-EDS confirmed the importance of the C-O-C group, -OH group and carbonyl group from polysaccharides and proteins in Cu2+ sorption by EPS. These findings suggest the potential of EPS produced by sulfate-reducing bacteria for the removal of Cu(II) ion from aqueous solution.

Hydrogenotrophic sulfate reduction in a gas-lift bioreactor operated at 9 degrees C.

The viability of low temperature sulfate reduction with hydrogen as electron donor was studied with a bench-scale gas-lift bioreactor (GLB) operated at 9 degrees C. Prior to the GLB experiment, the temperature range of sulfate reduction of the inoculum was assayed. The results of the temperature gradient assay indicated that the inoculum was a psychrotolerant mesophilic enrichment culture that had an optimal temperature for sulfate reduction of 31 degrees C, and minimum and maximum temperatures of 7 degrees C and 41 degrees C, respectively. In the GLB experiment at 9 degrees C, a sulfate reduction rate of 500-600 mg L(-1) d(-1), corresponding to a specific activity of 173 mg SO(4)(2-) g VSS(-1) d(-1), was obtained. The electron flow from the consumed H(2)-gas to sulfate reduction varied between 27% and 52%, while the electron flow to acetate production decreased steadily from 15% to 5%. No methane was produced. Acetate was produced from CO(2) and H(2) by homoacetogenic bacteria. Acetate supported the growth of some heterotrophic sulfate-reducing bacteria. The sulfate reduction rate in the GLB was limited by the slow biomass growth rate at 9 degrees C and low biomass retention in the reactor. Nevertheless, this study demonstrated the potential sulfate reduction rate of psychrotolerant sulfate-reducing mesophiles at sub-optimal temperature.

Desulfovibrio portus sp. nov., a novel sulfate-reducing bacterium in the class Deltaproteobacteria isolated from an estuarine sediment.

A strictly anaerobic, mesophilic, sulfate-reducing bacterial strain (MSL79T) isolated from an estuarine sediment in the Sea of Japan of the Japanese islands was characterized phenotypically and phylogenetically. Cells were Gram-negative, motile with a polar flagellum, non-spore-forming, curved rods. Cells had desulfoviridin and c-type cytochrome. Catalase and oxidase activities were not detected. The optimum NaCl concentration for growth was 2.0% (wt/vol). The optimum temperature was 35 degrees C and the optimum pH was 6.5. Strain MSL79T utilized H2, formate, pyruvate, lactate, fumarate, malate, succinate, ethanol, propanol and butanol as electron donors for sulfate reduction. The organic electron donors were incompletely oxidized to mainly acetate. Sulfite and thiosulfate were used as electron acceptors with lactate as an electron donor. Without electron acceptors, pyruvate, fumarate and malate supported the growth. The genomic DNA G+C content was 62.1 mol%. Menaquinone MK-6(H2) was the major respiratory quinone. Major cellular fatty acids were C16:0, iso-C15:0, anteiso-C15:0, iso-C17:0, anteiso-C17:0 and iso-C17:1omega9. Phylogenetic analysis based on the 16S rRNA gene sequence as well as the alpha-subunit of dissimilatory sulfite reductase gene sequence assigned the strain to the family Desulfovibrionaceae within the class Deltaproteobacteria. The closest validly described species based on the 16S rRNA gene sequences were Desulfovibrio aespoeensis (sequence similarity; 95.0%) and Desulfovibrio profundus (94.3%). On the basis of the significant differences in the 16S rRNA gene sequences and the phenotypic characteristics between strain MSL79T and each of the most closely related species, Desulfovibrio portus sp. nov. is proposed. The type strain is MSL79T (=JCM 14722T=DSM 19338T).

Resonance Raman fingerprinting of multiheme cytochromes from the cytochrome c3 family.

Resonance Raman (RR) spectroscopy was used to investigate conformational characteristics of the hemes of several ferricytochromes of the cytochrome c3 family, electron transfer proteins isolated from the periplasm and membranes of sulfate-reducing bacteria. Our analysis concentrated on the low-frequency region of the RR spectra, a fingerprint region that includes vibrations for heme-protein C-S bonds [nu(C(a)S)]. It has been proposed that these bonds are directly involved in the electron transfer process. The three groups of tetraheme cytochrome c3 analyzed, namely Type I cytochrome c (3) (TpIc (3)s), Type II cytochrome c (3) (TpIIc (3)s) and Desulfomicrobium cytochromes c3, display different frequency separations for the two nu(C(a)S) lines that are similar among members of each group. These spectral differences correlate with differences in protein structure observed among the three groups of cytochromes c3. Two larger cytochromes of the cytochrome c3 family display RR spectral characteristics for the nu(C(a)S) lines that are closer to TpIIc3 than to TpIc3. Two other multiheme cytochromes from Desulfovibrio that do not belong to the cytochrome c3 family display nu(C(a)S) lines with reverse relative areas in comparison with the latter family. This RR study shows that the small differences in protein structure observed among these cytochrome c3 correlate to differences on the heme-protein bonds, which are likely to have an impact upon the protein function, making RR spectroscopy a sensitive and useful tool for characterizing these cytochromes.

Sulfato/thiosulfato reducing bacteria characterization by FT-IR spectroscopy: a new approach to biocorrosion control.

Sulfato and Thiosulfato Reducing Bacteria (SRB, TRB) can induce corrosion process on steel immersed in seawater. This phenomenon, called biocorrosion, costs approximatively 5 billion euros in France each year. We provide the first evidence that Fourier Transformed InfraRed (FTIR) spectroscopy is a competitive technique to evaluate the sulfurogen flora involved in biocorrosion in comparison with time consuming classical identification methods or PCR analyses. A great discrimination was obtained between SRB, TRB and some contamination bacteria known to be present in seawater and seem to be able to reduce sulfate under particular conditions. Moreover, this preliminary study demonstrates that FTIR spectroscopic and genotypic results present a good correlation (these results are confirmed by other data obtained before or later, data not shown here). The advantages gained by FTIR spectroscopy are to give information on strain phenotype and bacterial metabolism which are of great importance in corrosion processes.

Zero valent iron as an electron-donor for methanogenesis and sulfate reduction in anaerobic sludge.

Zero valent iron (ZVI) is a reactive media commonly utilized in permeable reactive barriers (PRBs). Sulfate reducing bacteria are being considered for the immobilization of heavy metals in PRBs. The purpose of this study was to evaluate the potential of ZVI as an electron donor for sulfate reduction in natural mixed anaerobic cultures. The ability of methanogens to utilize ZVI as an electron-donor was also explored since these microorganisms often compete with sulfate reducers for common substrates. Four grades of ZVI of different particle sizes (1.120, 0.149, 0.044, and 0.010 mm diameter) were compared as electron donor in batch bioassays inoculated with anaerobic bioreactor sludge. Methanogenesis was evaluated in mineral media lacking sulfate. Sulfate reduction was evaluated in mineral media containing sulfate and the specific methanogenic inhibitor, 2-bromoethane sulfonate. ZVI contributed to significant increases in methane production and sulfate reduction-compared to endogenous substrate controls. The rates of methane formation or sulfate reduction were positively correlated with the surface area of ZVI. The highest rates of 0.310 mmol CH4 formed/mol Fe0.day and 0.804 mmol SO4(2-) reduced/mol Fe0.day were obtained with the finest grade of ZVI (0.01 mm). The results demonstrate that ZVI is readily utilized as a slow-release electron donor for methanogenesis and sulfate reduction in anaerobic sludge; and therefore, has a promising potential in bioremediation applications.

The effect of sulfate-reducing bacteria on adsorption of 137Cs by soils from arid and tropical regions.

Soils from different climatic regions of Australia were studied to determine their adsorption of (137)Cs, and the effect of microbial sulfate reduction on this adsorption. The soils consisted of a surface and regolith samples from the site of a proposed low and intermediate level radioactive waste repository in arid South Australia, and two red earth loam soils from an experimental plot in the tropical Northern Territory. The process of bacterial sulfate reduction substantially decreased the adsorption of (137)Cs to the arid and tropical soils, although extended incubation resulted in greater adsorption to the regolith sample. This could have implications for the mobility of radionuclides entering these soil ecosystems.

Sediment microbial community composition and methylmercury pollution at four mercury mine-impacted sites.

Mercury pollution presents a globally significant threat to human and ecosystem health. An important transformation in the mercury cycle is the conversion of inorganic mercury to methylmercury, a toxic substance that negatively affects neurological function and bioaccumulates in food chains. This transformation is primarily bacterially mediated, and sulfate-reducing bacteria (SRB) have been specifically implicated as key mercury methylators in lake and estuarine sediments. This study used phospholipid fatty acid (PLFA) analysis to investigate sediment microbial community composition at four abandoned mercury mine-impacted sites in the California Coast Range: the Abbott, Reed, Sulphur Bank, and Mt. Diablo mines. Differences in watershed and hydrology among these sites were related to differences in microbial community composition. The Abbott and Sulphur Bank mines had the highest levels of methylmercury. Floc (a type of precipitate that forms when acid mine drainage contacts lake or river water) and sediment samples differed in terms of several important environmental variables and microbial community composition, but did not have statistically different methylmercury concentrations. Quantification of PLFA biomarkers for SRB (10Mel6:0 for Desulfobacter and i17:1 for Desulfovibrio) revealed that Desulfobacter and Desulfovibrio organisms made up higher percentages of overall microbial biomass at the Sulphur Bank and Mt. Diablo mines than at the Abbott and Reed mines. Correlations between these SRB biomarker fatty acids and methylmercury concentrations suggest that Desulfobacter and Desulfovibrio organisms may contribute to methylmercury production in the Abbott, Reed, and Sulphur Bank mines but may not be important contributors to methylmercury in the Mt. Diablo Mine.

Characterization of electrostatic binding sites of extracellular polymers by linear programming analysis of titration data.

Electrostatic binding sites of extracellular polymeric substances (EPS) were characterized from titration data using linear programming analysis. Test results for three synthetic solutions of given solutes comprising amino, carboxyl, and phenolic groups indicated that this method was able to identify the electrostatic binding sites. For the six sites with pK(a) between 3 and 10, the estimated pK(a) deviated 0.11 +/- 0.09 from the theoretical values, and the estimated concentrations deviated 3.0% +/- 0.9% from the actual concentrations. Two EPS samples were then extracted from a hydrogen-producing sludge (HPS) and a sulfate-reducing biofilm (SRB). Analysis of charge excess data in titration from pH 3 to 11 indicated that the EPS of HPS comprised of five electrostatic binding sites with pK(a) ranging from 3 to 11. The pK(a) values of these binding sites and the possible corresponding functional groups were pK(a) 4.8 (carboxyl), pK(a) 6.0 (carboxyl/phosphoric), pK(a) 7.0 (phosphoric), pK(a) 9.8 (amine/phenolic), and pK(a) 11.0 (hydroxyl). EPS of the SRB comprised five of similar binding sites (with corresponding pK(a) values of 4.4, 6.0, 7.4, 9.4, and 11.0), plus one extra site at pK(a) 8.2, which was likely corresponding to the sulfhydryl group. The total electrostatic binding site concentration of EPS extracted from HPS were 10.88 mmol/g-EPS, of which the highest concentration was from the site of pK(a) 11.0. The corresponding values for the EPS extracted from SRB were 16.44 mmol/g-EPS and pK(a) 4.4. The total concentrations of electrostatic binding sites found in this study were 20- to 30-fold of those reported for bacterial cell surface, implying that EPS might be more crucial in biosorption of metals than bacterial cell surface in wastewater treatment and in bioremediation.

Monoalkylether phospholipids in the sulfate-reducing bacteria Desulfosarcina variabilis and Desulforhabdus amnigenus.

In this study, cellular lipid compositions of two mesophilic sulfate-reducing bacteria were analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS). In Desulfosarcina variabilis and Desulforhabdus amnigenus, alkylether-containing phospholipids were detected which had previously only been found in significant amounts in deeply branching hyperthermophilic bacteria and archaea. Combining information from HPLC-MS analysis and chemical degradation experiments, ether lipids were identified as 1-alkyl-2-acyl-phosphatidyl ethanolamines, glycerols and cholines. In Desulforhabdus amnigenus, n-penta-, n-hexa- and n-heptadecyl ethers were present (in order of decreasing abundance), whereas Desulfosarcina variabilis solely contained n-hexadecyl ether side chains.

Reclassification of Desulfobacterium phenolicum as Desulfobacula phenolica comb. nov. and description of strain SaxT as Desulfotignum balticum gen. nov., sp. nov.

A mesophilic, sulfate-reducing bacterium (strain SaxT) was isolated from marine coastal sediment in the Baltic Sea and originally described as a 'Desulfoarculus' sp. It used a large variety of substrates, ranging from simple organic compounds and fatty acids to aromatic compounds as electron donors. Autotrophic growth was possible with H2, CO2 and formate in the presence of sulfate. Sulfate, thiosulfate and sulfite were used as electron acceptors. Sulfur and nitrate were not reduced. Fermentative growth was obtained with pyruvate, but not with fumarate or malate. Substrate oxidation was usually complete leading to CO2, but at high substrate concentrations acetate accumulated. CO dehydrogenase activity was observed, indicating the operation of the CO dehydrogenase pathway (reverse Wood pathway) for CO2 fixation and complete oxidation of acetyl-CoA. The rod-shaped cells were 0.8-1.0 microm wide and 1.5-2.5 microm long. Spores were not produced and cells stained Gram-negative. The temperature limits for growth were between 10 and 42 degrees C (optimum growth at 28-32 degrees C). Growth was observed at salinities ranging from 5 to 110 g NaCl l(-1), with an optimum at 10-25 g NaCl l(-1). The G+C content of the DNA was 62.4 mol%. Vitamins were required for growth. Based on the 16S rRNA gene sequence, strain SaxT represents a new genus within the delta-subclass of the Proteobacteria. The name Desulfotignum balticum gen. nov., sp. nov. is proposed. After the 16S rDNA sequences of all members of the genus Desulfobacterium were published (GenBank accession nos. AJ237601-AJ237604, AJ237606, AJ237607), the need to reclassify most members of the genus Desulfobacterium became obvious due to their strong phylogenetic affiliation to other genera. Here, we propose to reclassify Desulfobacterium phenolicum as Desulfobacula phenolica comb. nov. Desulfotignum balticum, Desulfobacterium phenolicum and Desulfobacula toluolica contain cellular fatty acids which have so far only been found in members of the genus Desulfobacter.

Phylogenetic diversity of a SRB-rich marine biofilm.

This study was conducted to characterize the phylogenetic diversity of a corrosive marine biofilm based on 16S rDNA. Results of phylogenetic analysis indicated that, out of the 112 clones developed, 52 clones (46.4%) were affiliated with two families of sulfate-reducing bacteria: Desulfovibrionaceae and Desulfobacteriaceae. Another 44 clones (39.3%) were affiliated with the Clostridiaceae family of low G+C, gram-positive bacteria. Three clones (2.7%) were closely related to Chlorobium vibrioforme, a green sulfur bacterium.

A fast and simple turbidimetric method for the determination of sulfate in sulfate-reducing bacterial cultures.

A standard turbidimetric assay for the determination of sulfate in water was modified with the objective of achieving a quick and simple method for monitoring the decrease of sulfate in cultures of sulfate-reducing bacteria. The effects of sulfate concentration, mixing time and the ratio of sample to conditioning reagent were optimized using a central composite face-centered response surface model design. The results suggested that a mixing time of 30 s resulted in smaller absorbance variance, the variance in absorbance measurements tended to increase with concentration of sulfate and that the ratio between the amount of conditioning reagent and sample had no significant influence on the absorbance variance. The modified assay thus developed is simple and quick, and covers a comparatively large sulfate concentration range (0-5 mM) compared to the standard turbidimetric assay.

Community structure, cellular rRNA content, and activity of sulfate-reducing bacteria in marine arctic sediments.

The community structure of sulfate-reducing bacteria (SRB) of a marine Arctic sediment (Smeerenburgfjorden, Svalbard) was characterized by both fluorescence in situ hybridization (FISH) and rRNA slot blot hybridization by using group- and genus-specific 16S rRNA-targeted oligonucleotide probes. The SRB community was dominated by members of the Desulfosarcina-Desulfococcus group. This group accounted for up to 73% of the SRB detected and up to 70% of the SRB rRNA detected. The predominance was shown to be a common feature for different stations along the coast of Svalbard. In a top-to-bottom approach we aimed to further resolve the composition of this large group of SRB by using probes for cultivated genera. While this approach failed, directed cloning of probe-targeted genes encoding 16S rRNA was successful and resulted in sequences which were all affiliated with the Desulfosarcina-Desulfococcus group. A group of clone sequences (group SVAL1) most closely related to Desulfosarcina variabilis (91.2% sequence similarity) was dominant and was shown to be most abundant in situ, accounting for up to 54. 8% of the total SRB detected. A comparison of the two methods used for quantification showed that FISH and rRNA slot blot hybridization gave comparable results. Furthermore, a combination of the two methods allowed us to calculate specific cellular rRNA contents with respect to localization in the sediment profile. The rRNA contents of Desulfosarcina-Desulfococcus cells were highest in the first 5 mm of the sediment (0.9 and 1.4 fg, respectively) and decreased steeply with depth, indicating that maximal metabolic activity occurred close to the surface. Based on SRB cell numbers, cellular sulfate reduction rates were calculated. The rates were highest in the surface layer (0.14 fmol cell(-1) day(-1)), decreased by a factor of 3 within the first 2 cm, and were relatively constant in deeper layers.

Sediment microbial community structure and mercury methylation in mercury-polluted Clear Lake, California.

Spatial and temporal variations in sediment microbial community structure in a eutrophic lake polluted with inorganic mercury were identified using polar lipid fatty acid (PLFA) analysis. Microbial community structure was strongly related to mercury methylation potential, sediment organic carbon content, and lake location. Pore water sulfate, total mercury concentrations, and organic matter C/N ratios showed no relationships with microbial community structure. Seasonal changes and changes potentially attributable to temperature regulation of bacterial membranes were detectable but were less important influences on sediment PLFA composition than were differences due to lake sampling location. Analysis of biomarker PLFAs characteristic of Desulfobacter and Desulfovibrio groups of sulfate-reducing bacteria suggests that Desulfobacter-like organisms are important mercury methylators in the sediments, especially in the Lower Arm of Clear Lake.

Heteronuclear NMR and soft docking: an experimental approach for a structural model of the cytochrome c553-ferredoxin complex.

The combination of docking algorithms with NMR data has been developed extensively for the studies of protein-ligand interactions. However, to extend this development for the studies of protein-protein interactions, the intermolecular NOE constraints, which are needed, are more difficult to access. In the present work, we describe a new approach that combines an ab initio docking calculation and the mapping of an interaction site using chemical shift variation analysis. The cytochrome c553-ferredoxin complex is used as a model of numerous electron-transfer complexes. The 15N-labeling of both molecules has been obtained, and the mapping of the interacting site on each partner, respectively, has been done using HSQC experiments. 1H and 15N chemical shift analysis defines the area of both molecules involved in the recognition interface. Models of the complex were generated by an ab initio docking software, the BiGGER program (bimolecular complex generation with global evaluation and ranking). This program generates a population of protein-protein docked geometries ranked by a scoring function, combining relevant stabilization parameters such as geometric complementarity surfaces, electrostatic interactions, desolvation energy, and pairwise affinities of amino acid side chains. We have implemented a new module that includes experimental input (here, NMR mapping of the interacting site) as a filter to select the accurate models. Final structures were energy minimized using the X-PLOR software and then analyzed. The best solution has an interface area (1037.4 A2) falling close to the range of generally observed recognition interfaces, with a distance of 10.0 A between the redox centers.