Biological role of nickel

Photodynamic Inactivation of Bacteria Using Nickel(II) Complexes with Catecholate and Phenanthroline Ligands

Metal complexes activated by light can combat infections by triggering the photodynamic inactivation of bacteria. Herein, we report six mixed-ligand nickel(II) complexes with the formulation [Ni(NN)2(L)] (1-6), where NN represents an N,N-donor phenanthroline ligand, specifically 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), while L is an O,O donor bidentate ligand derived from catechol (cat2-, in 1, 3, 5) or esculetin (esc2-, in 2, 4, 6). The paramagnetic d8 octahedral complexes demonstrated good dark and photostability in the solution phase and exhibited significant light absorption in the visible (400-700 nm) region. When exposed to low-energy visible light, these complexes demonstrated significant photodynamic inactivation activity against both Gram-(+) Staphylococcus aureus (S. aureus) and Gram-(-) Escherichia coli (E. coli) bacteria. This resulted in minimum inhibitory concentration (MIC) values ranging from 0.31-9.49 μM. The activity was caused by the cell-damaging singlet oxygen species produced by the complexes under light exposure. Notably, the complexes showed no bacterial inhibition activity under dark conditions. This study marks the first examples of Ni(II) complexes designed for light-triggered antibacterial activity, illuminating the path for Ni(II)-based non-macrocyclic complexes for antibacterial PDT applications.

Genetic Mapping for QTL Associated with Seed Nickel and Molybdenum Accumulation in the Soybean 'Forrest' by 'Williams 82' RIL Population

Understanding the genetic basis of seed Ni and Mo is essential. Since soybean is a major crop in the world and a major source for nutrients, including Ni and Mo, the objective of the current research was to map genetic regions (quantitative trait loci, QTL) linked to Ni and Mo concentrations in soybean seed. A recombinant inbred line (RIL) population was derived from a cross between 'Forrest' and 'Williams 82' (F × W82). A total of 306 lines was used for genotyping using 5405 single nucleotides polymorphism (SNP) markers using Infinium SNP6K BeadChips. A two-year experiment was conducted and included the parents and the RIL population. One experiment was conducted in 2018 in North Carolina (NC), and the second experiment was conducted in Illinois in 2020 (IL). Logarithm of the odds (LOD) of ≥2.5 was set as a threshold to report identified QTL using the composite interval mapping (CIM) method. A wide range of Ni and Mo concentrations among RILs was observed. A total of four QTL (qNi-01, qNi-02, and qNi-03 on Chr 2, 8, and 9, respectively, in 2018, and qNi-01 on Chr 20 in 2020) was identified for seed Ni. All these QTL were significantly (LOD threshold > 2.5) associated with seed Ni, with LOD scores ranging between 2.71-3.44, and with phenotypic variance ranging from 4.48-6.97%. A total of three QTL for Mo (qMo-01, qMo-02, and qMo-03 on Chr 1, 3, 17, respectively) was identified in 2018, and four QTL (qMo-01, qMo-02, qMo-03, and qMo-04, on Chr 5, 11, 14, and 16, respectively) were identified in 2020. Some of the current QTL had high LOD and significantly contributed to the phenotypic variance for the trait. For example, in 2018, Mo QTL qMo-01 on Chr 1 had LOD of 7.8, explaining a phenotypic variance of 41.17%, and qMo-03 on Chr 17 had LOD of 5.33, with phenotypic variance explained of 41.49%. In addition, one Mo QTL (qMo-03 on Chr 14) had LOD of 9.77, explaining 51.57% of phenotypic variance related to the trait, and another Mo QTL (qMo-04 on Chr 16) had LOD of 7.62 and explained 49.95% of phenotypic variance. None of the QTL identified here were identified twice across locations/years. Based on a search of the available literature and of SoyBase, the four QTL for Ni, identified on Chr 2, 8, 9, and 20, and the five QTL associated with Mo, identified on Chr 1, 17, 11, 14, and 16, are novel and not previously reported. This research contributes new insights into the genetic mapping of Ni and Mo, and provides valuable QTL and molecular markers that can potentially assist in selecting Ni and Mo levels in soybean seeds.

Synthesis, characterization, solution chemistry and anticancer activity of [NiCl2(Ph2P-N(R)-PPh2)] (R = 2-CH2Py, CH2Ph and p-tol) complexes

In this work three Ni²⁺ complexes with general formula [NiCl₂(Ph₂P-N(R)-PPh₂)], R = 2-CH₂Py (Py = pyridine) - 1, CH₂Ph (Ph = phenyl) - 2 and p-tol (p-tol = p-tolyl) - 3, were synthesized and characterized. These complexes were obtained in high yield by the reaction of NiCl₂.6H₂O and the corresponding diphenylphosphinoamine ligand (Ph₂P-N(R)-PPh₂) in CH₂Cl₂/MeOH (1:1) solution, at room temperature (∼25 °C), and characterized by ¹H and ³¹P {¹H} NMR, vibrational spectroscopy in the infrared region, electronic spectroscopy in the UV-Vis regions, elemental analysis (%C, %H, %N) and single-crystal X-ray diffraction. The solution chemistry was studied in CDCl₃/dmso-d⁶ (dimethylsulfoxide) or neat dmso-d⁶ using complex 2 as a model. The complexes were evaluated as cytotoxic agents against two cancer cells lines, A549 (lung cancer cells), B16F10 (melanoma cells) and the health cells HaCaT (human epithelial keratinocytes).

Biogenesis and Application of Nickel Nanoparticles: A Review

Biogenic synthesis of Nanoparticles (NPs) is attractive due to their ecological benefits and cheap, rapid, and sustainable nature. Among them, Nickel Oxide NPs (NiO-NPs) are acquired for their varied catalytic and clinical applications, as they have antibacterial, antifungal, cytotoxic, anticancer, antioxidant, remediation, and enzyme inhibition properties. Though several chemical-dependent methods were applied for the fabrication of nanoparticles, due to their substantial disadvantages, mainly toxicity and higher cost synthesis methods, the more secure, greener, eco-friendly, cost-effective, and synthetic methods are in demand. Greener approaches can take away the arduousness and complications of physicochemical methods. The present review is aimed at displaying the recent advancement related to the catalytic activity, antimicrobial activity, cytotoxicity, and antioxidant application of green synthesized Nickle. In this study, nickle oxide nanoparticles have been highlighted along with their sustainable synthesis options.

Nickel and arsenite-induced differential oxidative stress and antioxidant responses in two Anabaena species

In recent years, release of chemical pollutants has increased due to anthropogenic activities. Heterocystous filamentous cyanobacteria constitute dominant paddy microflora and are excellent biofertilizers augmenting rice productivity. Cyanobacteria are frequently exposed to toxic metals, nickel and arsenic are one of the major toxicants present. We exposed two species of diazotrophic cyanobacteria Anabaena sp. PCC 7120 and Anabaena doliolum, to sub-lethal concentrations (15.0 and 9.0 μM) of Ni²⁺ and (17.0 and 11 mM) of arsenite (AsIII) and analyzed at different days of treatments (0, 1, 7, and 15 days) for oxidative damage and antioxidative biomarkers. Lipid peroxidation was enhanced (1.5- to 2.5-fold increase in MDA content), indicating damaging effects of Ni²⁺ and As(III) on membrane. Although Ni²⁺ and As(III), both induced oxidative stress in both species, Anabaena PCC 7120 experienced less stress than A. doliolum. This could be explained by a higher activity of antioxidant enzymes catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) in Anabaena PCC 7120 (4.6-, 2.0- and 1.4-fold [Ni²⁺ ] 3.2-, 2.5-, and 2.08-fold [As]) compared to A. doliolum (4.2-, 2.5-, and 1.3-fold [Ni²⁺ ] and 3.2-, 3.33-, and 1.8-fold [As]). Moreover, superoxide dismutase registered less inhibition in Anabaena sp. PCC 7120 (1.5 and 1.8) compared to A. doliolum (1.8 and 2.3) under Ni²⁺ and As(III) stress. In addition to, IBR revealed that As(III) imposes severe impact on both strain, however, A. doliolum suffers most. Therefore, the study demonstrates interspecies variation in survival strategy of two Anabaena species and difference in potential of two different toxicants to produce oxidative stress.

Influence of inhibitors on the adhesion of SRB to the stainless steel in circulating cooling water

Influence of the surface characteristics of three stainless steels (SS304, 316L and 317) and presence of scale inhibitors on adhesion kinetics of sulfate reducing bacteria (SRB) in circulating cooling water, were investigated by evaluating surface free energy, adhesion kinetic constants in a parallel plate flow chamber. Results show that the surface free energy values of SS317, SS316L and SS304 are -31.69, -24.18 and -13.92 mJ m^-2, respectively. SS317 surface had higher surface hydrophobicity than SS316L and SS304. In the process of bacteria cells adhesion onto SS surfaces, electrostatic interaction for SS is slightly more than hydrophobic interaction. The number of adhering bacteria and the adhesion kinetic constants are different on the three types of stainless steel. The adhesion kinetic constants for SS317 and 316L are greater than that for SS304, which are 0.0354, 0.0282 and 0.0190 min^-1, respectively. Scale inhibitors of hydrosy ethyl fork phosphonic acid (HEDP) and phosphono butane-1, 2, 4-tricarboxylic acid (PBTCA) have a certain influence on the initial adhesion of bacteria cell and adhesion kinetics constants are reduced in the presence of HEDP and PBTCA.

A newly synthesized nickel chelate can selectively target and overcome multidrug resistance in cancer through redox imbalance both in vivo and in vitro

Induction of undesired toxicity and emergence of multidrug resistance (MDR) are the major obstacles for cancer treatment. Moreover, aggressive cancers are less sensitive towards existing chemotherapeutics. Therefore, selective targeting of cancers without inducing undesired side effects and designing proper strategies to overcome MDR has utmost importance in modern chemotherapy. Previously we revealed the anticancer properties of some transition metal chelates of Schiff base, but the effectiveness of nickel complex is still unrevealed. Herein, we synthesized and characterized a Schiff base nickel chelate, nickel-(II) N-(2-hydroxyacetophenone) glycinate (NiNG), through different spectroscopic means. NiNG proves to be a broad spectrum anticancer agent with considerable efficacy to overcome MDR in cancer. Antiproliferative effects of NiNG was evaluated using drug-resistant (CEM/ADR5000; NIH-MDR-G185; EAC/Dox), drug-sensitive aggressive (Hct116; CCRF-CEM; EAC/S) and normal (NIH-3T3) cells that reveal the selective nature of NiNG towards drug resistant and sensitive cancer cells without inducing any significant toxicity in normal cells. Moreover, NiNG involves reactive oxygen species (ROS)-mediated redox imbalance for induction of caspase 3-dependent apoptosis in aggressive drug-sensitive Hct116 and drug-resistant NIH-MDR-G185 cells through disruption of mitochondrial membrane potential. Moreover, intraperitoneal (i.p.) application of NiNG at non-toxic doses caused significant increase in the life-span of Swiss albino mice bearing sensitive and doxorubicin-resistant subline of Ehrlich ascites carcinoma cells. It is noteworthy that, in vitro NiNG can only overcome P-glycoprotein-mediated MDR while in vivo NiNG can overcome MRP1-mediated MDR in cancer. Therefore, NiNG has therapeutic potential to target and overcome MDR in cancer.

In-vitro anti-inflammatory and mosquito larvicidal efficacy of nickel nanoparticles phytofabricated from aqueous leaf extracts of Aegle marmelos Correa

In recent years there is a tremendous growth in the interdisciplinary world of nanotechnology across the globe and emergence of its potential applications remains as a big revolution to the industry. Fusion of green nanotechnology and medicine represents one of the major breakthroughs of modern science with the aim of developing nanomaterials for diagnosis, treatment, prevention of various diseases and overall improving health for the beneficial of mankind. In the present study phytofabrication of nickel nanoparticles (nickel NPs) was carried out by using indigenous Aegle marmelos Correa aqueous leaf extracts as a reducing, stabilizing and capping agents. Nickel NPs were characterized by UV-spectroscopy, FTIR, XRD, SEM, AFM and TGA studies. Phytosynthesis of nickel NPs was monitored both at room temperature (25°C) and at 60°C for 5h. The green synthesis of triangular shape nickel NPs phytofabricated from A. marmelos Correa aqueous leaf extracts having face centered cubic structure showing an average particle size of 80-100nm which is in consistent with the particle size calculated by XRD Scherer equation. We further explored and compared nickel NPs of A. marmelos Correa with crude leaf extracts of A. marmelos Correa for its in-vitro anti-inflammatory and mosquito larvicidal efficacy against three blood feeding parasites. The results obtained clearly gives an idea that nickel NPs of A. marmelos Correa (NiNPs of AmC) possess an enhanced anti-inflammatory and larvicidal activity when compared to crude leaf extracts of A. marmelos Correa.

Complexation of nickel (II) ion with B3 vitamin in aqueous dimethyl sulfoxide

The stability change of nickel(II) ion complexes including one and two nicotinamide (B3 vitamin) molecules in aqueous dimethyl sulfoxide (XDMSO = 0–0.85 m.f.) was studied at 298.2±0.1 K and 0.25 ionic strength value (NaClO4) using the potentiometric method. The first stage constant of complexation increased until organic solvent concentration was 0.5 m.f. and reduced at higher DMSO content. The difference between complex and central ions solvation is a dominating contribution into the Gibbs energy change of mononicotinamide complex formation reaction. When the second ligand molecule was bonded into the coordination compound, the nicotinamide contribution to ΔtrGr rose and became prevailing at XDMSO = 0.7–0.85. The ligand was found to replace a water molecule in the coordination sphere of the cation according to spectrophotometric study results.

Activated acetic acid by carbon fixation on (Fe,Ni)S under primordial conditions

In experiments modeling the reactions of the reductive acetyl-coenzyme A pathway at hydrothermal temperatures, it was found that an aqueous slurry of coprecipitated NiS and FeS converted CO and CH3SH into the activated thioester CH3-CO-SCH3, which hydrolyzed to acetic acid. In the presence of aniline, acetanilide was formed. When NiS-FeS was modified with catalytic amounts of selenium, acetic acid and CH3SH were formed from CO and H2S alone. The reaction can be considered as the primordial initiation reaction for a chemoautotrophic origin of life.

Structure-function relationships among the nickel-containing hydrogenases

The enzymology of the heterodimeric (NiFe) and (NiFeSe) hydrogenases, the monomeric nickel-containing hydrogenases plus the multimeric F420-(NiFe) and NAD(+)-(NiFe) hydrogenases are summarized and discussed in terms of subunit localization of the redox-active nickel and non-heme iron clusters. It is proposed that nickel is ligated solely by amino acid residues of the large subunit and that the non-heme iron clusters are ligated by other cysteine-rich polypeptides encoded in the hydrogenase operons which are not necessarily homologous in either structure or function. Comparison of the hydrogenase operons or putative operons and their hydrogenase genes indicate that the arrangement, number and types of genes in these operons are not conserved among the various types of hydrogenases except for the gene encoding the large subunit. Thus, the presence of the gene for the large subunit is the sole feature common to all known nickel-containing hydrogenases and unites these hydrogenases into a large but diverse gene family. Although the different genes for the large subunits may possess only nominal general derived amino acid homology, all large subunit genes sequenced to date have the sequence R-X-C-X-X-C fully conserved in the amino terminal region of the polypeptide chain and the sequence of D-P-C-X-X-C fully conserved in the carboxyl terminal region. It is proposed that these conserved motifs of amino acids provide the ligands required for the binding of the redox-active nickel. The existing EXAFS (Extended X-ray Absorption Fine Structure) information is summarized and discussed in terms of the numbers and types of ligands to the nickel and the various redox species of nickel defined by EPR spectroscopy. New information concerning the ligands to nickel is presented based on site-directed mutagenesis of the gene encoding the large subunit of the (NiFe) hydrogenase-1 of Escherichia coli. Based on considerations of the biochemical, molecular and biophysical information, ligand environments of the nickel in different redox states of the (NiFe) hydrogenase are proposed.

Resistance to cadmium, cobalt, zinc, and nickel in microbes

The divalent cations of cobalt, zinc, and nickel are essential nutrients for bacteria, required as trace elements at nanomolar concentrations. However, at micro- or millimolar concentrations, Co2+, Zn2+, and Ni2+ (and "bad ions" without nutritional roles such as Cd2+) are toxic. These cations are transported into the cell by constitutively expressed divalent cation uptake systems of broad specificity, i.e., basically Mg2+ transport systems. Therefore, in case of a heavy metal stress, uptake of the toxic ions cannot be reduced by a simple down-regulation of the transport activity. As a response to the resulting metal toxicity, metal resistance determinants evolved which are mostly plasmid-encoded in bacteria. In contrast to that of the cation Hg2+, chemical reduction of Co2+, Zn2+, Ni2+, and Cd2+ by the cell is not possible or sensible. Therefore, other than mutations limiting the ion range of the uptake system, only two basic mechanisms of resistance to these ions are possible (and were developed by evolution): intracellular complexation of the toxic metal ion is mainly used in eucaryotes; the cadmium-binding components are phytochelatins in plant and yeast cells and metallothioneins in animals, plants, and yeasts. In contrast, reduced accumulation based on an active efflux of the cation is the primary mechanism developed in procaryotes and perhaps in Saccharomyces cerevisiae. All bacterial cation efflux systems characterized to date are plasmid-encoded and inducible but differ in energy-coupling and in the number and types of proteins involved in metal transport and in regulation. In the gram-positive multiple-metal-resistant bacterium Staphylococcus aureus, Cd2+ (and probably Zn2+) efflux is catalyzed by the membrane-bound CadA protein, a P-type ATPase. However, a second protein (CadC) is required for full resistance and a third one (CadR) is hypothesized for regulation of the resistance determinant. The czc determinant from the gram-negative multiple-metal-resistant bacterium Alcaligenes eutrophus encodes proteins required for Co2+, Zn2+, and Cd2+ efflux (CzcA, CzcB, and CzcC) and regulation of the czc determinant (CzcD). In the current working model CzcA works as a cation-proton antiporter, CzcB as a cation-binding subunit, and CzcC as a modifier protein required to change the substrate specificity of the system from Zn2+ only to Co2+, Zn2+, and Cd2+.

Toxicity and carcinogenicity of nickel compounds

The toxicity and carcinogenicity of nickel compounds are considered in three broad categories: (1) systemic toxicology, (2) molecular toxicology, and (3) carcinogenicity. The systemic toxicity of nickel compounds is examined based upon human and animal studies. The major organs affected are discussed in three categories: (1) kidney, (2) immune system, and (3) other organs. The second area of concentration is molecular toxicology, which will include a discussion of the chemistry of nickel, its binding to small and large molecular weight ligands, and, finally, its cellular effects. The third major area involves a discussion of the carcinogenicity and genotoxicity of nickel compounds. This section focuses on mechanisms, using studies conducted in vivo and in vitro. It also includes a discussion of the assessment of the carcinogenicity of nickel compounds.

The three classes of hydrogenases from sulfate-reducing bacteria of the genus Desulfovibrio

Three types of hydrogenases have been isolated from the sulfate-reducing bacteria of the genus Desulfovibrio. They differ in their subunit and metal compositions, physico-chemical characteristics, amino acid sequences, immunological reactivities, gene structures and their catalytic properties. Broadly, the hydrogenases can be considered as 'iron only' hydrogenases and nickel-containing hydrogenases. The iron-sulfur-containing hydrogenase ([Fe] hydrogenase) contains two ferredoxin-type (4Fe-4S) clusters and an atypical iron-sulfur center believed to be involved in the activation of H2. The [Fe] hydrogenase has the highest specific activity in the evolution and consumption of hydrogen and in the proton-deuterium exchange reaction and this enzyme is the most sensitive to CO and NO2-. It is not present in all species of Desulfovibrio. The nickel-(iron-sulfur)-containing hydrogenases [( NiFe] hydrogenases) possess two (4Fe-4S) centers and one (3Fe-xS) cluster in addition to nickel and have been found in all species of Desulfovibrio so far investigated. The redox active nickel is ligated by at least two cysteinyl thiolate residues and the [NiFe] hydrogenases are particularly resistant to inhibitors such as CO and NO2-. The genes encoding the large and small subunits of a periplasmic and a membrane-bound species of the [NiFe] hydrogenase have been cloned in Escherichia (E.) coli and sequenced. Their derived amino acid sequences exhibit a high degree of homology (70%); however, they show no obvious metal-binding sites or homology with the derived amino acid sequence of the [Fe] hydrogenase. The third class is represented by the nickel-(iron-sulfur)-selenium-containing hydrogenases [( NiFe-Se] hydrogenases) which contain nickel and selenium in equimolecular amounts plus (4Fe-4S) centers and are only found in some species of Desulfovibrio. The genes encoding the large and small subunits of the periplasmic hydrogenase from Desulfovibrio (D.) baculatus (DSM 1743) have been cloned in E. coli and sequenced. The derived amino acid sequence exhibits homology (40%) with the sequence of the [NiFe] hydrogenase and the carboxy-terminus of the gene for the large subunit contains a codon (TGA) for selenocysteine in a position homologous to a codon (TGC) for cysteine in the large subunit of the [NiFe] hydrogenase. EXAFS and EPR studies with the 77Se-enriched D. baculatus hydrogenase indicate that selenium is a ligand to nickel and suggest that the redox active nickel is ligated by at least two cysteinyl thiolate and one selenocysteine selenolate residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Transport and accumulation of nickel ions in the cyanobacterium Anabaena cylindrica

The uptake of nickel ions by the cyanobacterium Anabaena cylindrica was studied. Nickel transport was dependent on the membrane potential of the cells and the rate of uptake was decreased in the dark or by the addition of inhibitors, including uncouplers and electron transport inhibitors, which decreased or abolished the membrane potential of cells. The transport process obeyed hyperbolic kinetics, with a high affinity (apparent Km = 17 +/- 11 (SEM) nM) and low turnover number (maximum velocity = 22.3 +/- 5.4 (SEM) pmol h-1 mg dry wt-1 of cells or flux rate of 3.1 nmol h-1 m-2 of plasma membrane surface area). The process was also apparently specific for Ni2+, the rate being unaffected by the presence of a range of other metal ions in large excess. Equilibrium experiments showed that, over a range of nickel ion concentrations, the cells concentrated Ni2+ by a factor of 2700 +/- 240 (SEM)-fold, corresponding to a chemical diffusion potential for Ni2+ of 101 mV. It was concluded that the cells transport nickel ions by a carrier-facilitated transport process with the concentration factor for the ions being determined by the cell membrane potential according to the Nernst equation.

The use of nickel to probe the role of hydrogen metabolism in cyanobacterial nitrogen fixation

The hydrogenase activities of the heterocystous cyanobacteria Anabaena cylindrica and Mastigocladus laminosus are nickel dependent, based on their inability to consume hydrogen with various electron acceptors or produce hydrogen with dithionite-reduced methyl viologen, after growth in nickel-depleted medium. Upon addition of nickel ions to nickel-deficient cultures of A. cylindrica, the hydrogenase activity recovered in a manner which was protein synthesis-dependent, the recovery being inhibited by chloramphenicol. We have used the nickel dependence of the hydrogenase as a probe of the possible roles of H2 consumption in enhancing nitrogen fixation, and particularly for protecting nitrogenase against oxygen inhibition. Although at the usual growth temperatures (25 degrees for A. cylindrica and 40 degrees for M. laminosus), the cells consume H2 vigorously in an oxyhydrogen reaction after growth in the presence of nickel ions, we have not found that the reaction confers any significant additional protection of nitrogenase, either at aerobic pO2 (for both organisms) or at elevated pO2 (for A. cylindrica). However, at elevated temperatures (e.g., 40 degrees for A. cylindrica and 48 degrees for M. laminosus) a definite protective effect was observed. At these temperatures both organisms rapidly lost acetylene reduction activity under aerobic conditions. When hydrogen gas (10%) was present, the cells retained approximately 50% of the nitrogenase activity observed under anaerobic conditions (argon gas phase). No such protection by hydrogen gas was observed with nickel-deficient cells. Studies with cell-free extracts of A. cylindrica showed that the predominant effect of temperature was not due to thermal inactivation of nitrogenase.

Regulation of the synthesis of hydrogenase (formate hydrogen-lyase linked) of E. coli

The regulation of synthesis of the hydrogenase which is a component of the formate hydrogen-lyase complex was studied by means of a strain of Escherichia coli possessing a transcriptional fusion of the hydrogenase gene (hyd) with the lacZ gene (hyd::lac fusion). Formation of active hydrogenase in the wild strain requires the presence of nickel in the medium; transcription of the hyd gene, however, is independent from the presence of Ni2+. Ni2+ addition to Ni2+-prestarved cells did not lead to any activation of presumptive hydrogenase apoprotein. Regulatory mutants were isolated in which nitrate repression of hyd::lac expression was relieved. Two main classes of regulatory mutants were identified: (i) Mutants with a defect in nitrate reductase; (ii) mutants with a cis-dominant regulatory mutation closely linked to the hyd::lac fusion. In the presence of formate which acts as an inducer, the hyd::lac fusion was also expressed under aerobic conditions. The results infer that nitrate repression of transcription of the hydrogenase structural gene is not effected by nitrate itself but requires the function of the electron transport chain leading to nitrate and that mutations in the promoter/operator region of the hyd cistron may confer insensitivity to redox control both by oxygen and nitrate.

The bioenergetics of methanogenesis

The reduction of CO2 or any other methanogenic substrate to methane serves the same function as the reduction of oxygen, nitrate or sulfate to more reduced products. These exergonic reactions are coupled to the production of usable energy generated through a charge separation and a protonmotive-force-driven ATPase. For the understanding of how methanogens derive energy from C-1 unit reduction one must study the biochemistry of the chemical reactions involved and how these are coupled to the production of a charge separation and subsequent electron transport phosphorylation. Data on methanogenesis by a variety of organisms indicates ubiquitous use of CH3-S-CoM as the final electron acceptor in the production of methane through the methyl CoM reductase and of 5-deazaflavin as a primary source of reducing equivalents. Three known enzymes serve as catalysts in the production of reduced 5-deazaflavin: hydrogenase, formate dehydrogenase and CO dehydrogenase. All three are potential candidates for proton pumps. In the organisms that must oxidize some of their substrate to obtain electrons for the reduction of another portion of the substrate to methane (e.g., those using formate, methanol or acetate), the latter two enzymes may operate in the oxidizing direction. CO2 is the most frequent substrate for methanogenesis but is the only substrate that obligately requires the presence of H2 and hydrogenase. Growth on methanol requires a B12-containing methanol-CoM methyl transferase and does not necessarily need any other methanogenic enzymes besides the methyl-CoM reductase system when hydrogenase is present. When bacteria grow on methanol alone it is not yet clear if they get their reducing equivalents from a reversal of methanogenic enzymes, thus oxidizing methyl groups to CO2. An alternative (since these and acetate-catabolizing methanogens possess cytochrome b) is electron transport and possible proton pumping via a cytochrome-containing electron transport chain. Several of the actual components of the methanogenic pathway from CO2 have been characterized. Methanofuran is apparently the first carbon-carrying cofactor in the pathway, forming carboxy-methanofuran. Formyl-FAF or formyl-methanopterin (YFC, a very rapidly labelled compound during 14C pulse labeling) has been implicated as an obligate intermediate in methanogenesis, since methanopterin or FAF is an essential component of the carbon dioxide reducing factor in dialyzed extract methanogenesis. FAF also carries the carbon at the methylene and methyl oxidation levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Anaerobic waste stabilization

The present knowledge of the microbiology, physiology and regulation of anaerobic digestion in conventional or advanced processes is reviewed. In all systems the carbon flow from biopolymers to biogas is determined by syntrophic interactions of fermentative or acetogenic bacteria with methanogens at the level of interspecies hydrogen transfer. Inhibitors or heavy metal ions may interfere at different levels. The stabilization of waste at mesophilic and thermophilic temperatures is compared and the process stability as well as the inactivation of pathogens is discussed. Characteristics of conventional digestion systems and of recently developed advanced processes with solids and liquids uncoupling are compared and selection criteria with respect to the type of sludge are outlined. Areas of future research for a better understanding of the biochemistry, the physiology and the regulation of the degradation of pollutants are suggested.

Nickel transport in Methanobacterium bryantii

Methanobacterium bryantii, grown autotrophically on H2-CO2, transported nickel against a concentration gradient by a high-affinity system (Km = 3.1 microM). The system had a pH optimum of 4.9 and a temperature optimum of 49 degrees C with an energy of activation of 7.8 kcal/mol (ca. 32.6 kJ/mol). A headspace of H2-CO2 (4:1, vol/vol) was required for maximum rate of transport. The system was highly specific for nickel and was unaffected by high levels of all monovalent and divalent ions tested (including Mg2+) with the sole exception of Co2+. Kinetic experiments indicated that accumulated nickel became increasingly incorporated into cofactor F430 and protein. Nickel transport was inhibited by nigericin, monensin, and gramicidin but not by carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone, carbonyl cyanide-m-chlorophenyl hydrazone, N,N'-dicyclohexylcarbodiimide, valinomycin plus potassium, or acetylene. The ineffectiveness of carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone, carbonyl cyanide-m-chlorophenyl hydrazone, and N,N'-dicyclohexylcarbodiimide may be related to difficulties in the penetration of these compounds through the outer cell barriers. Nickel uptake was greatly stimulated by an artificially imposed pH gradient (inside alkaline). The data suggest that nickel transport is not dependent on the membrane potential or on intracellular ATP, but is coupled to proton movement.

Studies on the Ni-content of the centriole

Nickel-containing organelles or subcellular structures have not yet been described in the literature; only some Ni-containing enzymes or "factors" acting at the cellular level have been studied. In the present study the nickel-content of centrioles and basal bodies were detected by using a new histochemical method. The centrioles and basal bodies are able to take up nickel. Evidence has also been presented that low concentrations of Ni (10(-5) M) enhance the growth rate of Tetrahymena.