Conductive magnetic nanowires accelerated electron transfer between C1020 carbon steel and Desulfovibrio vulgaris biofilm

Microbial biofilms are behind microbiologically influenced corrosion (MIC). Sessile cells in biofilms are many times more concentrated volumetrically than planktonic cells in the bulk fluids, thus providing locally high concentrations of chemicals. More importantly, "electroactive" sessile cells in biofilms are capable of utilizing extracellularly supplied electrons (e.g., from elemental Fe) for intracellular reduction of an oxidant such as sulfate in energy metabolism. MIC directly caused by anaerobic biofilms is classified into two main types based on their mechanisms: extracellular electron transfer MIC (EET-MIC) and metabolite MIC (M-MIC). Sulfate-reducing bacteria (SRB) are notorious for their corrosivity. They can cause EET-MIC in carbon steel, but they can also secrete biogenic H2S to corrode other metals such as Cu directly via M-MIC. This study investigated the use of conductive magnetic nanowires as electron mediators to accelerate and thus identify EET-MIC of C1020 by Desulfovibrio vulgaris. The presence of 40 ppm (w/w) nanowires in ATCC 1249 culture medium at 37 °C resulted in 45 % higher weight loss and 57 % deeper corrosion pits after 7-day incubation. Electrochemical tests using linear polarization resistance and potentiodynamic polarization supported the weight loss data trend. These findings suggest that conductive magnetic nanowires can be employed to identify EET-MIC. The use of insoluble 2 μm long nanowires proved that the extracellular section of the electron transfer process is a bottleneck in SRB MIC of carbon steel.

Enhanced bioremediation of acid mine-influenced groundwater with micro-sized emulsified corn oil droplets (MOD) and sulfate-reducing bacteria (Desulfovibrio vulgaris) in a microcosm assay

High concentrations of metals and sulfates in acid mine drainage (AMD) are the cause of the severe environmental hazard that mining operations pose to the surrounding ecosystem. Little study has been conducted on the cost-effective biological process for treating high AMD. The current research investigated the potential of the proposed carbon source and sulfate reduction bacteria (SRB) culture in achieving the bioremediation of sulfate and heavy metals. This work uses individual and combinatorial bioaugmentation and bio-stimulation methods to bioremediate acid-mine-influenced groundwater in batch microcosm experiments. Bioaugmentation and bio-stimulation methods included pure culture SRB (Desulfovibrio vulgaris) and microsized oil droplet (MOD) by emulsifying corn oil. The research tested natural attenuation (T 1), bioaugmentation (T2), biostimulation (T3), and bioaugmentation plus biostimulation (T4) for AM-contaminated groundwater remediation. Bioaugmentation and bio-stimulation showed the greatest sulfate reduction (75.3%) and metal removal (95-99%). Due to carbon supply scarcity, T1 and T2 demonstrated 15.7% and 27.8% sulfate reduction activities. Acetate concentrations in T3 and T4 increased bacterial activity by providing carbon sources. Metal bio-precipitation was substantially linked with sulfate reduction and cell growth. SEM-EDS study of precipitates in T3 and T4 microcosm spectra indicated peaks for S, Cd, Mn, Cu, Zn, and Fe, indicating metal-sulfide association for metal removal precipitates. The MOD provided a constant carbon source for indigenous bacteria, while Desulfovibrio vulgaris increased biogenic sulfide synthesis for heavy metal removal.

Antibiofilm assay for antimicrobial peptides combating the sulfate-reducing bacteria Desulfovibrio vulgaris

In medical, environmental, and industrial processes, the accumulation of bacteria in biofilms can disrupt many processes. Antimicrobial peptides (AMPs) are receiving increasing attention in the development of new substances to avoid or reduce biofilm formation. There is a lack of parallel testing of the effect against biofilms in this area, as well as in the testing of other antibiofilm agents. In this paper, a high-throughput screening was developed for the analysis of the antibiofilm activity of AMPs, differentiated into inhibition and removal of a biofilm. The sulfate-reducing bacterium Desulfovibrio vulgaris was used as a model organism. D. vulgaris represents an undesirable bacterium, which is considered one of the major triggers of microbiologically influenced corrosion. The application of a 96-well plate and steel rivets as a growth surface realizes real-life conditions and at the same time establishes a flexible, simple, fast, and cost-effective assay. All peptides tested in this study demonstrated antibiofilm activity, although these peptides should be individually selected depending on the addressed aim. For biofilm inhibition, the peptide DASamP1 is the most suitable, with a sustained effect for up to 21 days. The preferred peptides for biofilm removal are S6L3-33, in regard to bacteria reduction, and Bactenecin, regarding total biomass reduction.

Influence of nutrition on Cu corrosion by Desulfovibrio vulgaris in anaerobic environment

The eutrophication of seawater is not only harmful to the environment, but also influence microbes' proliferation and then influence biocorrosion of marine engineering materials to a great extent. This study investigated the microbiologically influenced corrosion (MIC) of Cu immersed in the Desulfovibrio vulgaris (a sulfate reducing bacterium) medium with four defined nutritional degrees: total nutrition, P lacking, N lacking, and P&N lacking. When D. vulgaris was cultured in more nutritional medium, more H₂S was generated and more serious corrosion of Cu occurred. The concentration of H₂S corresponding to the medium with total nutrition was as high as 4.9 × 10⁴(±913.0) ppm. The weight loss of Cu in medium with total nutrition increased by at least 50% compared with other nutritional conditions. The depth of pitting pits on Cu increased obviously with more abundant nutrient elements N and P. The electrochemical tests supported the weight loss and also showed that an obvious passivation zone was formed on the anodic polarization curve. This indicated that a protective film was formed on the surface of Cu against uniform corrosion. The analyses of thermodynamics and experiment data indicated that metabolite MIC (M-MIC) account for the Cu corrosion by D. vulgaris.

Anaerobic Transformation and Detoxification of Sulfamethoxazole by Sulfate-Reducing Enrichments and Desulfovibrio vulgaris

Sulfamethoxazole (SMX) is a veterinary antibiotic that is not efficiently removed from wastewater by routine treatment and therefore can be detected widely in the environment. Here, we investigated whether microbial anaerobic transformation can contribute to the removal of SMX in constructed systems. We enriched SMX-transforming mixed cultures from sediment of a constructed wetland and from digester sludge of a wastewater treatment plant. Transformation of SMX was observed in both sulfate-reducing and methanogenic cultures, whereas nitrate-reducing cultures showed no SMX transformation. In sulfate-reducing cultures, up to 90% of an initial SMX concentration of 100-250 μM was removed within 6 weeks of incubation, and the experiments demonstrated that the transformation was microbially catalyzed. The transformation products in sulfate-reducing cultures were identified as the reduced and isomerized forms of the isoxazole SMX moiety. The transformation products did not spontaneously reoxidize to SMX after oxygen exposure, and their antibacterial activity was significantly decreased compared to SMX. Population analyses in sequential transfers of the sulfate-reducing cultures revealed a community shift toward the genus Desulfovibrio. We therefore tested a deposited strain of Desulfovibrio vulgaris Hildenborough for its capacity to transform SMX and observed the same transformation products and similar transformation rates as in the enrichment cultures. Our work suggests that an initial anaerobic step in wastewater treatment can reduce the concentration of SMX in effluents and could contribute to decreased SMX concentrations in the environment.

Sulfur Isotope Fractionation by Sulfate-Reducing Microbes Can Reflect Past Physiology

Sulfur (S) isotope fractionation by sulfate-reducing microorganisms is a direct manifestation of their respiratory metabolism. This fractionation is apparent in the substrate (sulfate) and waste (sulfide) produced. The sulfate-reducing metabolism responds to variability in the local environment, with the response determined by the underlying genotype, resulting in the expression of an "isotope phenotype". Sulfur isotope phenotypes have been used as a diagnostic tool for the metabolic activity of sulfate-reducing microorganisms in the environment. Our experiments with Desulfovibrio vulgaris Hildenborough (DvH) grown in batch culture suggest that the S isotope phenotype of sulfate respiring microbes may lag environmental changes on time scales that are longer than generational. When inocula from different phases of growth are assayed under the same environmental conditions, we observed that DvH exhibited different net apparent fractionations of up to -9‰. The magnitude of fractionation was weakly correlated with physiological parameters but was strongly correlated to the age of the initial inoculum. The S isotope fractionation observed between sulfate and sulfide showed a positive correlation with respiration rate, contradicting the well-described negative dependence of fractionation on respiration rate. Quantitative modeling of S isotope fractionation shows that either a large increase (≈50×) in the abundance of sulfate adenylyl transferase (Sat) or a smaller increase in sulfate transport proteins (≈2×) is sufficient to account for the change in fractionation associated with past physiology. Temporal transcriptomic studies with DvH imply that expression of sulfate permeases doubles over the transition from early exponential to early stationary phase, lending support to the transport hypothesis proposed here. As it is apparently maintained for multiple generations (≈1-6) of subsequent growth in the assay environment, we suggest that this fractionation effect acts as a sort of isotopic "memory" of a previous physiological and environmental state. Whatever its root cause, this physiological hysteresis effect can explain variations in fractionations observed in many environments. It may also enable new insights into life at energetic limits, especially if its historical footprint extends deeper than generational.

Reductive precipitation of sulfate and soluble Fe(III) by Desulfovibrio vulgaris: Electron donor regulates intracellular electron flow and nano-FeS crystallization

Fully understanding the metabolism of SRB provides fundamental guidelines for allowing the microorganisms to provide more beneficial services in water treatment and resource recovery. The electron-transfer pathway of sulfate respiration by Desulfovibrio vulgaris is well studied, but still partly unresolved. Here we provide deeper insight by comprehensively monitoring metabolite changes during D. vulgaris metabolism with two electron donors, lactate and pyruvate, in presence or absence of citrate-chelated soluble Fe^III as an additional competing electron acceptor. H₂ was produced from lactate oxidation to pyruvate, but pyruvate oxidation produced mostly formate. Accumulation of lactate-originated H₂ during lag phases inhibited pyruvate transformation to acetate. Sulfate reduction was initiated by lactate-originated H₂, but MQ-mediated e^- flow initiated sulfate reduction without delay when pyruvate was the donor. When H₂-induced electron flow gave priority to Fe^III reduction over sulfate reduction, the long lag phase before sulfate reduction shortened the time for iron-sulfide crystallite growth and led to smaller mackinawite (Fe_1+xS) nanocrystallites. Synthesizing all the results, we propose that electron flow from lactate or pyruvate towards SO₄^2- reduction to H₂S are through at least three routes that are regulated by the e^- donor (lactate or pyruvate) and the presence or absence of another e^- acceptor (Fe^III here). These routes are not competing, but complementary: e.g., H₂ or formate production and oxidation were necessary for sulfite and disulfide/trisulfide reduction to sulfide. Our study suggests that the e^- donor provides a practical tool to regulate and optimize SRB-predominant bioremediation systems.

Resonance assignment of DVU2108 that is part of the Orange Protein complex in Desulfovibrio vulgaris Hildenborough

We report the 94 % assignment of DVU2108, a protein belonging to the Orange Protein family, that in Desulfovibrio vulgaris Hildenborough forms a protein complex named the Orange Protein complex. This complex has been shown to be implicated in the cell division of this organism. DVU2108 is a conserved protein in anaerobic microorganisms and in Desulfovibrio gigas the homologous protein was isolated with a novel Mo-Cu cluster non-covalently attached to the polypeptide chain. However, the heterologously produced DVU2108 did not contain any bound metal. These assignments provide the means to characterize the interaction of DVU2108 with the proteins that form the Orange Protein complex using NMR methods.

Triple-resonance methods for complete resonance assignment of aromatic protons and directly bound heteronuclei in histidine and tryptophan residues

A set of three experiments is described which correlate aromatic resonances of histidine and tryptophan residues with amide resonances in 13C/15N-labelled proteins. Provided that backbone 1H and 15N positions of the sequentially following residues are known, this results in sequence-specific assignment of histidine 1H(delta2)/13C(delta2) and 1H(epsilon1)/13C(epsilon1) as well as tryptophan 1H(delta1)/13C(delta1), 1H(zeta2)/13C(zeta2), 1H(eta2)/13C(eta2), 1H(epsilon3)/13C(epsilon3), 1H(zeta3)/13C(zeta3) and 1H(epsilon1)/15N(epsilon1) chemical shifts. In the reverse situation, these residues can be located in the 1H-(15)N correlation map to facilitate backbone assignments. It may be chosen between selective versions for either of the two amino acid types or simultaneous detection of both with complete discrimination against phenylalanine or tyrosine residues in each case. The linkages between delta-proton/carbon and the remaining aromatic as well as backbone resonances do not rely on through-space interactions, which may be ambiguous, but exclusively employ one-bond scalar couplings for magnetization transfer instead. Knowledge of these aromatic chemical shifts is the prerequisite for the analysis of NOESY spectra, the study of protein-ligand interactions involving histidine and tryptophan residues and the monitoring of imidazole protonation states during pH titrations. The new methods are demonstrated with five different proteins with molecular weights ranging from 11 to 28 kDa.

Displacement of iron by zinc at the diiron site of Desulfovibrio vulgaris rubrerythrin: X-ray crystal structure and anomalous scattering analysis

X-ray crystal structures of recombinant Desulfovibrio (D.) vulgaris rubrerythrin (Rbr) have shown a diiron site, whereas the crystal structure of Rbr "as-isolated" from D. vulgaris was reported to contain a mixed Zn,Fe binuclear site. To investigate the possibility that zinc had displaced iron during isolation or crystallization of the "as-isolated" D. vulgaris Rbr, the X-ray crystal structure of recombinant D. vulgaris all-iron Rbr that had been incubated with excess zinc sulfate prior to crystallization, yielding a protein labeled Zn,FeRbr, was solved. Analysis of the anomalous scattering data obtained at two different wavelengths showed that zinc had displaced a significant proportion of iron from both iron centers of the diiron site, and that no iron had been displaced from the [Fe(SCys)(4)] site. UV-visible absorption spectra of the redissolved Zn,FeRbr crystals showed 30-40% retention of oxo-bridged diferric sites, and the redissolved crystals had 37% of the peroxidase specific activity of the starting all-iron Rbr, which, together with the crystallographic results, indicate a predominant mixture of Fe1,Fe2 and Zn1,Zn2 sites. The structure of the Zn(Fe)1,Fe(Zn)2 binuclear site in the Zn,FeRbr crystals was very similar to that of the Zn,Fe binuclear site reported for the "as-isolated" D. vulgaris Rbr, including tetrahedral four-coordination at the Zn(Fe)1 site. The diiron sites in the recombinant Zn,FeRbr crystals were likely at least partially reduced during synchrotron irradiation. Our results suggest that the mixed-metal binuclear site reported for the "as-isolated" D. vulgaris Rbr could be due to displacement of iron from a native diiron site by adventitious zinc during isolation and/or crystallization, and that reduced diiron and dizinc sites can adopt very similar structures in Rbr.

Hybrid-cluster protein (HCP) from Desulfovibrio vulgaris (Hildenborough) at 1.6 A resolution

The three-dimensional structure of the hybrid cluster protein from Desulfovibrio vulgaris (Hildenborough) has been determined at 1.6 A resolution using synchrotron X-ray radiation. The protein can be divided into three domains: an N-terminal mainly alpha-helical domain and two similar domains comprising a central beta-sheet flanked by alpha-helices. The protein contains two 4Fe clusters with an edge-to-edge distance of 10.9 A. Four cysteine residues at the N-terminus of the protein are ligands to the iron atoms of a conventional [4Fe-4S] cubane cluster. The second cluster has an unusual asymmetric structure and has been named the hybrid cluster to reflect the variety of protein ligands, namely two mu-sulfido bridges, two mu(2)-oxo bridges, and a further disordered bridging ligand. Anomalous differences in data collected at 1.488 A and close to the iron edge at 1.743 A have been used to confirm the identity of the metal and sulfur atoms. The hybrid cluster is buried in the center of the protein, but is accessible through a large hydrophobic cavity that runs the length of domain 3. Hydrophobic channels have previously been identified as access routes to the active centers in redox enzymes with gaseous substrates. The hybrid cluster is also accessible by a hydrophilic channel. The [4Fe-4S] cubane cluster is close to an indentation on the surface of the protein and can also be approached on the opposite side by a long solvent channel. At the present time, neither the significance of these channels nor, indeed, the function of the hybrid cluster protein is known.

Characterization of novel proteins based on known protein structures

The genome sciences face the challenge to characterize structure and function of a vast number of novel genes. Sequence search techniques are used to infer functional and structural information from similarities to experimentally characterized genes or proteins. The persistent goal is to refine these techniques and to develop alternative and complementary methods to increase the range of reliable inference.Here, we focus on the structural and functional assignments that can be inferred from the known three-dimensional structures of proteins. The study uses all structures in the Protein Data Bank that were known by the end of 1997. The protein structures released in 1998 were then characterized in terms of functional and structural similarity to the previously known structures, yielding an estimate of the maximum amount of information on novel protein sequences that can be obtained from inference techniques. The 147 globular proteins corresponding to 196 domains released in 1998 have no clear sequence similarity to previously known structures. However, 75 % of the domains have extensive structure similarity to previously known folds, and most importantly, in two out of three cases similarity in structure coincides with related function. In view of this analysis, full utilization of existing structure data bases would provide information for many new targets even if the relationship is not accessible from sequence information alone. Currently, the most sophisticated techniques detect of the order of one-third of these relationships.

NADH peroxidase activity of rubrerythrin

P. S. Alban et al. (J. Appl. Microbiol. (1998) 85, 875-882) reported that a mutant H2O2-resistant strain of Spirullum (S.) volutans showed constitutive overexpression of a protein whose amino acid sequence and molecular weight closely resembled that of a subunit of rubrerythrin, a non-heme iron protein with no known function. They also reported that the mutant strain, but not the wild-type, showed NADH peroxidase activity. Here we demonstrate that rubrerythrin and nigerythrin from Desulfovibrio vulgaris and rubrerythrin from Clostridium perfringens show NADH peroxidase activities in an in vitro system containing NADH, hydrogen peroxide, and a bacterial NADH oxidoreductase. The peroxidase specific activities of the rubrerythrins with the "classical" heme peroxidase substrate, o-dianisidine, are many orders of magnitude lower than that of horseradish peroxidase. These results are consistent with the phenotype of the H2O2-resistant strain of S. volutans. The reaction of reduced (i.e., all-ferrous) rubrerythrin with excess O2 takes several minutes, whereas the anaerobic reaction of reduced rubrerythrin with hydrogen peroxide is on the millisecond time scale and results in full oxidation of all iron centers to their ferric states. Rubrerythrins could, thus, function as the terminal components of NADH peroxidases in air-sensitive bacteria and archaea.

Modulation of the redox potentials of FMN in Desulfovibrio vulgaris flavodoxin: thermodynamic properties and crystal structures of glycine-61 mutants

Mutants of the electron-transfer protein flavodoxin from Desulfovibrio vulgaris were made by site-directed mutagenesis to investigate the role of glycine-61 in stabilizing the semiquinone of FMN by the protein and in controlling the flavin redox potentials. The spectroscopic properties, oxidation-reduction potentials, and flavin-binding properties of the mutant proteins, G61A/N/V and L, were compared with those of wild-type flavodoxin. The affinities of all of the mutant apoproteins for FMN and riboflavin were less than that of the wild-type apoprotein, and the redox potentials of the two 1-electron steps in the reduction of the complex with FMN were also affected by the mutations. Values for the dissociation constants of the complexes of the apoprotein with the semiquinone and hydroquinone forms of FMN were calculated from the redox potentials and the dissociation constant of the oxidized complex and used to derive the free energies of binding of the FMN in its three oxidation states. These showed that the semiquinone is destabilized in all of the mutants, and that the extent of destabilization tends to increase with increasing bulkiness of the side chain at residue 61. It is concluded that the hydrogen bond between the carbonyl of glycine-61 and N(5)H of FMN semiquinone in wild-type flavodoxin is either absent or severely impaired in the mutants. X-ray crystal structure analysis of the oxidized forms of the four mutant proteins shows that the protein loop that contains residue 61 is moved away from the flavin by 5-6 A. The hydrogen bond formed between the backbone nitrogen of aspartate-62 and O(4) of the dimethylisoalloxazine of the flavin in wild-type flavodoxin is absent in the mutants. Reliable structural information was not obtained for the reduced forms of the mutant proteins, but if the mutants change conformation when the flavin is reduced to the semiquinone, to facilitate hydrogen bonding between N(5)H and the carbonyl of residue 61, then the change must be different from that known to occur in wild-type flavodoxin.

Regulation of oxidation-reduction potentials through redox-linked ionization in the Y98H mutant of the Desulfovibrio vulgaris [Hildenborough] flavodoxin: direct proton nuclear magnetic resonance spectroscopic evidence for the redox-dependent shift in the pKa of Histidine-98

Flavodoxin from Desulfovibrio vulgaris is a low molecular weight (15 000 Da) acidic flavoprotein that contains a single flavin mononucleotide (FMN) cofactor. A distinguishing feature of the flavodoxin family is the exceptionally low midpoint potential of the semiquinone/hydroquinone couple. Tyrosine-98, which flanks the outer or si face of the FMN, plays an important role in establishing the oxidation-reduction properties of the bound cofactor as demonstrated by the substitution of a number of amino acids at this position [Swenson, R. P., & Krey, G. D. (1994) Biochemistry 33, 8505-8514]. The midpoint potential for the semiquinone/hydroquinone couple increases substantially when basic residues are introduced at this position. The pH dependency in the Y98H mutant is consistent with a redox-linked ionization model in which the favorable electrostatic coupling between the imidazolium cation and the flavin hydroquinone anion is responsible for the higher potential. Such a model predicts an increase in the pKa of 1.5 units for His98 upon complete reduction of the FMN. In this study, proton nuclear magnetic resonance spectroscopy was used to directly determine the intrinsic pKa of His98 as a function of the redox state of the cofactor in this flavodoxin. Values for the pKa of His98 in the oxidized and fully reduced flavodoxin are 7.02 +/- 0.08 and 8.43 +/- 0.11, respectively, an increase in the pKa by 1.41 units, which conforms with the previous prediction. These results provide direct experimental proof of the redox-linked ionization of this residue and provides further evidence of the crucial role of electrostatic interactions, in this case, in the stabilization of the flavin hydroquinone anion. This phenomenon may represent a general mechanism in the modulation of the reduction potential of the flavin cofactor within flavoenzymes in which ionizable groups such as histidine in the active center change ionization states during the catalytic cycle.

Backbone dynamics of oxidized and reduced D. vulgaris flavodoxin in solution

Recombinant Desulfovibrio vulgaris flavodoxin was produced in Escherichia coli. A complete backbone NMR assignment for the two-electron reduced protein revealed significant changes of chemical shift values compared to the oxidized protein, in particular for the flavine mononucleotide (FMN)-binding site. A comparison of homo- and heteronuclear NOESY spectra for the two redox states led to the assumption that reduction is not accompanied by significant changes of the global fold of the protein. The backbone dynamics of both the oxidized and reduced forms of D. vulgaris flavodoxin were investigated using two-dimensional 15N-1H correlation NMR spectroscopy. T1, T2 and NOE data are obtained for 95% of the backbone amide groups in both redox states. These values were analysed in terms of the 'model-free' approach introduced by Lipari and Szabo [(1982) J. Am. Chem. Soc., 104, 4546-4559, 4559-4570]. A comparison of the two redox states indicates that in the reduced species significantly more flexibility occurs in the two loop regions enclosing FMN. Also, a higher amplitude of local motion could be found for the N(3)H group of FMN bound to the reduced protein compared to the oxidized state.

Structural origins of redox potentials in Fe-S proteins: electrostatic potentials of crystal structures

Redox potentials often differ dramatically for homologous proteins that have identical redox centers. For two types of iron-sulfur proteins, the rubredoxins and the high-potential iron-sulfur proteins (HiPIPs), no structural explanations for these differences have been found. We calculated the classical electrostatic potential at the redox site using static crystal structures of four rubredoxins and four HiPIPs to identify important structural determinants of their redox potentials. The contributions from just the backbone and polar side chains are shown to explain major features of the experimental redox potentials. For instance, in the rubredoxins, the presence of Val 44 versus Ala 44 causes a backbone shift that explains a approximately 50 mV lower redox potential in one of the four rubredoxins. This result is consistent with experimental redox potentials of five additional rubredoxins with known sequence. Also, we attribute the unusually lower redox potentials of two of the HiPIPs studied to a less positive electrostatic environment around their redox sites. Finally, molecular dynamics simulations of solvent around static rubredoxin crystal structures indicate that water alone is a major factor in dampening the contribution of charged side chains, in accord with experiments showing that mutations of surface charges produce relatively little effect on redox potentials.

Molecular characterization of two bacteriophages isolated from Desulfovibrio vulgaris NCIMB 8303 (Hildenborough)

A preliminary endonuclease restriction map of a bacteriophage isolated from Desulfovibrio vulgaris has been established. BamHI cleaved whole phage DNA into four fragments while HindIII cut the same DNA into seven fragments. Mapping studies succeeded in linking the four BamHI fragments into two DNA segments; however, no linkage between the two segments was detected. These data imply that two phages were induced from cultures of D. vulgaris and that the two segments represented the DNA from these phages. Support for this hypothesis came from size approximation of restriction enzyme fragments, electron micrographs, and density gradients.

Induction and partial purification of bacteriophages from Desulfovibrio vulgaris (Hildenborough) and Desulfovibrio desulfuricans ATCC 13541

Bacteriophages were induced from cultures of Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans ATCC 13541 by UV light. The optimum time of UV exposure was 1 min and the maximum yield of phage was obtained 9-10 h after UV treatment. The two phage preparations were compared by restriction enzyme analysis and Southern blot hybridization. The nucleic acid from both phages was cut by restriction endonucleases specific for double-stranded DNA. The phage DNAs from D. vulgaris and D. desulfuricans showed different restriction enzyme cleavage patterns. No homology was observed between a 25 kb probe from the D. vulgaris phage DNA and the phage DNA from D. desulfuricans. Protein profiles of the phages from both sources were also studied; the D. vulgaris phage contained two major bands corresponding to Mr values of 37 000 and 56 000 while the D. desulfuricans phage contained only one major band, of Mr 38 000.