Evaluation of startup and operation of four anaerobic processes treating a synthetic meat waste

Two continuous stirred tanks reactors (CSTR) and four anaerobic fluidized bed reactors (AFBR) were used to study the treatment of a synthetic meat waste during single-and two-stage anaerobic treatment. Four configurations were investigated; a single-stage CSTR and AFBR and the two-stage systems CSTR-AFBR and AFBR-AFBR. Startup of the anaerobic reactors was achieved within 50 days by use of a regime that included stepped increases in influent COD, methanol substitution of the substrate, and addition of essential trace metals such as cobalt and nickel. Two-stage reactors removed up to 85% of influent COD concentrations of 5000 mg/L, whereas the single-stage AFBR and CSTR removed 76 and 9%, respectively. The proportion of methane in the effluent gases increased as the influent COD concentration was increased. Volumetric production of methane was greatest for the first stage of the AFBR-AFBR system. Solids retention times calculated for the AFBRs ranged from 7 to 12 days, sufficient to support methanogenesis. The AFBRs and two-stage systems were more resistant to an influent pH shock from the operating value of pH 6.8 down to pH 3 than the CSTRs and single-stage reactors. It was concluded that high-rate anaerobic treatment systems were applicable to meat industry wastewaters and that two-stage digestion produced a better quality effluent.     

Bonding Form Analysis of Metals and Sulfur Fractionation in Methanol‐Grown Anaerobic Granular Sludge

This study investigates the metal and sulfur bonding form distribution in mesophilic (30 °C, pH 7) methanol‐grown anaerobic granular sludge from upflow anaerobic sludge bed reactors operating at an organic loading rate of 3.8 g CH₃OH‐COD/L d. This was achieved by applying a modified Tessier sequential extraction scheme to investigate the metal bonding forms and a sequential extraction scheme for sulfur and simultaneously extracted metals to granular sludge samples of the reactors after 0, 22, 35 and 43 days of operation. Metals were also determined in the sulfur extracts. Co and Ni predominated in their oxidizable bonding forms, which increased together with the pseudo‐total content during reactor operation. An omission of Co and Ni from the influent led to only a minor decline of the pseudo‐total content in the sludge, mainly from the acid‐soluble fraction. The ratio of simultaneously extracted metals (Co, Fe, Mn, Ni) to acid‐volatile sulfides was lower than 1, indicating that the sludge contained sufficient sulfide to bind the metals as metal monosulfides. The bioavailability of metals in the methanol‐grown anaerobic granular sludge investigated is therefore mainly controlled by sulfide formation/dissolution.     

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer??s and Parkinson??s disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.     

Improved resistance to transition metals of a cobalt-substituted alcohol dehydrogenase 1 from Saccharomyces cerevisiae

Cobalt-substituted alcohol dehydrogenase 1 was purified from a yeast culture of Saccharomyces cerevisiae. Its reactivity towards different transition metals was tested and compared with the native zinc enzyme. The cobalt enzyme displayed a catalytic efficiency 100-fold higher than that of the zinc enzyme. Copper, nickel and cadmium exerted a mixed-type inhibition, with a scale of inhibition efficiency: Cu(2+)>Ni(2+)>Cd(2+). In general, a higher resistance of the modified protein to the inhibitory action of transition metals was observed, with two orders of magnitude for copper I(50). The presence of nickel in the complexes enzyme-coenzyme-inhibitor-substrate resulted in a decrease of the ampholytic nature of the catalytic site. On the contrary, cadmium and copper exerted an enhancement of this parameter. Electrostatic or other types of interactions may be involved in conferring a good resistance in the basic pH range, making cobalt enzyme very suitable for biotechnological processes.     

Properties of anaerobic granular sludge as affected by yeast extract,cobalt and iron supplements

The effect of yeast extract (YE), iron (Fe) and cobalt (Co) on anaerobic bacterial granules grown in eight laboratory-scale upflow anaerobic sludge blanket reactors was investigated using a factorial design. The experiment was performed in three periods in which different chemical oxygen demand (COD) loading rates were applied to the reactors. The COD digestion rate and the specific activity of the bacteria were positively affected by supplementation of Fe and Co in the feed under a high COD loading rate. YE had a strong positive effect on the bacterial growth rate, but no significant effect on the specific activity of the bacteria. With Fe supplementation, an excellent COD digestion rate was maintained in the reactors, and addition of YE in the feed was not necessary. Granules with better settling properties were developed under a relatively low bacterial growth rate. With the increase in COD loading rate, the percentage of calcium increased rapidly in the granules from the reactors without YE supplementation. The bacteria grown under high COD loading rate and without an Fe supplement could be Fe-deficient. Methanothrix-like rod-shaped bacteria were dominant in the granules from all reactors. Correspondence to: N. Kosaric     

Effects of Nickel, Cobalt, and Molybdenum on Performance of Methanogenic Fixed-Film Reactors

The conversion of acetic acid to methane and carbon dioxide by a mixed methanogenic population from an anaerobic fixed-film digestor was stimulated by the addition of nickel (100 nM) and cobalt (50 nM) and especially by the addition of these elements in combination. Molybdenum addition (50 nM) was only slightly stimulatory when added in combination with both nickel and cobalt. The addition of these trace metals to anaerobic fixed-film digestors, which treat food processing waste, greatly enhanced reactor performance. Total gas and methane productions were increased 42%, greater volumes of waste could be effectively treated, and reactor residence time was shortened. However, the lag period for reactor start-up was not reduced. Tests showed that reactor performance was increased because trace nutrient addition allowed accumulation of a thicker methanogenic fixed film.     

Trace Metal Imaging of Sulfate-Reducing Bacteria and Methanogenic Archaea at Single-Cell Resolution by Synchrotron X-Ray Fluorescence Imaging

Metal cofactors are required for many enzymes in anaerobic microbial respiration. This study examined iron, cobalt, nickel, copper, and zinc in cellular and abiotic phases at the single-cell scale for a sulfate-reducing bacterium (Desulfococcus multivorans) and a methanogenic archaeon (Methanosarcina acetivorans) using synchrotron X-ray fluorescence microscopy. Relative abundances of cellular metals were also measured by inductively coupled plasma mass spectrometry. For both species, zinc and iron were consistently the most abundant cellular metals. M. acetivorans contained higher nickel and cobalt content than D. multivorans, likely due to elevated metal requirements for methylotrophic methanogenesis. Cocultures contained spheroid zinc sulfides and cobalt/copper sulfides.     

A Review of Processes Responsible for Metal Removal in Wetlands Treating Contaminated Mine Drainage

Many reports have documented wetlands removing a wide variety of contaminants in mine drainage, including aluminum, arsenic, cadmium, cobalt, copper, cyanide, iron, lead, manganese, nickel, selenium, uranium, and zinc. This article reviews biogeochemical processes responsible for their ability to transform and retain metals into insoluble forms. Shallow depth and large inputs of organic matter are key characteristics of wetlands that promote chemical and biological processes effecting metal removal. Aquatic macrophytes play an essential role in creating and maintaining this environment, but their uptake of metals usually accounts for a minor proportion of the total mass removed. Sorption onto organic matter is important in metal removal, particularly for copper, nickel, and uranium. Aluminum, iron, and manganese are often removed by hydrolysis, with the resulting acidification of water buffered by alkalinity produced in wetland sediments by anaerobic bacteria. Bacterial sulfate reduction accounts for much of this alkalinity. It can also contribute significantly to metal removal by formation of insoluble sulfides. Other important processes include the formation of insoluble carbonates, reduction to nonmobile forms, and adsorption onto iron oxides and hydroxides. Examples from field studies are presented throughout the review to illustrate these processes.     

Influence of pH shocks on trace metal dynamics and performance of methanol fed granular sludge bioreactors

The influence of pH shocks on the trace metal dynamics and performance of methanol fed upflow anaerobic granular sludge bed (UASB) reactors was investigated. For this purpose, two UASB reactors were operated with metal pre-loaded granular sludge (1mM Co, Ni and Fe; 30°C; 96h) at an organic loading rate (OLR) of 5gCOD l reactor^–1d^–1. One UASB reactor (R1) was inoculated with sludge that originated from a full scale reactor treating alcohol distillery wastewater, while the other reactor (R2) was inoculated with sludge from a full scale reactor treating paper mill wastewater. A 30h pH shock (pH 5) strongly affected the metal retention dynamics within the granular sludge bed in both reactors. Iron losses in soluble form with the effluent were considerable: 2.3 and 2.9% for R1 and R2, respectively, based on initial iron content in the reactors, while losses of cobalt and nickel in soluble form were limited. Sequential extraction of the metals from the sludge showed that cobalt, nickel, iron and sulfur were translocated from the residual to the organic/sulfide fraction during the pH shock in R2, increasing 34, 47, 109 and 41% in the organic/sulfide fraction, respectively. This is likely due to the modification of the iron sulfide precipitate stability, which influences the extractability of iron and trace metals. Such a translocation was not observed for the R1 sludge during the first 30h pH shock, but a second 4day pH shock induced significant losses of cobalt (18%), iron (29%) and sulfur (29%) from the organic/sulfide fraction, likely due to iron sulfide dissolution and concomitant release of cobalt. After the 30h pH shock, VFA accumulated in the R2 effluent, whereas both VFA and methanol accumulated in R1 after the 4day pH shock. The formed VFA, mainly acetate, were not converted to methane due to the loss of methanogenic activity of the sludge on acetate. The VFA accumulation gradually disappeared, which is likely to be related to out-competition of acetogens by methanogens. Zinc, copper and manganese supply did not have a clear effect on the acetate removal and methanol conversion, but zinc may have induced the onset of methanol degradation after day 152 in R1.     

Synthesis, characterisation, X-ray structure and biological activity of three new 5-formyluracil thiosemicarbazone complexes

Three new complexes of transition metals as copper, nickel and cobalt with 5-formyluracil thiosemicarbazone (H3ut) have been synthesised and characterised by single-crystal X-ray diffraction. In all compounds the ligand behaves as SNO terdentate. In the copper complex the coordination geometry is square pyramidal with the ligand lying on the basal plane and two water molecules that complete the metal environment, the nickel compound is surrounded by six donor atoms (three of the ligand, two water oxygen atoms and a chlorine atom) in an octahedral fashion, and cobalt also shows an octahedral geometry but determined only by two terdentate ligand molecules. These three compounds have been tested on human leukemic cell lines K562 and CEM. The nickel and cobalt complexes have demonstrated low activity in cell growth, while the copper complex that is more active has been tested also on a third leukemic human cell line (U937), but it was not able to induce apoptosis on all cell lines.     

Multiple roles of siderophores in free-living nitrogen-fixing bacteria

Free-living nitrogen-fixing bacteria in soils need to tightly regulate their uptake of metals in order to acquire essential metals (such as the nitrogenase metal cofactors Fe, Mo and V) while excluding toxic ones (such as W). They need to do this in a soil environment where metal speciation, and thus metal bioavailability, is dependent on a variety of factors such as organic matter content, mineralogical composition, and pH. Azotobacter vinelandii, a ubiquitous gram-negative soil diazotroph, excretes in its external medium catechol compounds, previously identified as siderophores, that bind a variety of metals in addition to iron. At low concentrations, complexes of essential metals (Fe, Mo, V) with siderophores are taken up by the bacteria through specialized transport systems. The specificity and regulation of these transport systems are such that siderophore binding of excess Mo, V or W effectively detoxifies these metals at high concentrations. In the topsoil (leaf litter layer), where metals are primarily bound to plant-derived organic matter, siderophores extract essential metals from natural ligands and deliver them to the bacteria. This process appears to be a key component of a mutualistic relationship between trees and soil diazotrophs, where tree-produced leaf litter provides a living environment rich in organic matter and micronutrients for nitrogen-fixing bacteria, which in turn supply new nitrogen to the ecosystem.     

Nutrient requirement for UASB process: a review

In literature, numerous studies regarding nutrients dosing are available in UASB reactors. Various nutrients and tracemetals used in UASB studies include nitrogen, phosphorous, yeast extract, magnesium, potassium, calcium, sulphur, iron, aluminium, zinc, nickel, cobalt, molybdenum, manganese, copper, boron, selenium, citrate, resazurine, EDTA, and hydrochloric acid. Often, there is a wide variation in the composition and quantification of nutrients and tracemetals, used to supplement the influent feed in UASB reactors. In this paper, nutrients and tracemetals formulations used in different studies on UASB reactors are compiled and critically analysed. In order to have uniformity, concentrations of nutrients and tracemetals have been converted into equivalent terms as g nutrients or tracemetals/g of waste COD. The ranges for this ratio for all the constituents of nutrients and tracemetals are given. Besides, the ranges associated with minimum start-up periods are also obtained. It is hoped that the information presented in this study would facilitate the nutrients dosing in UASB reactors.     

Nickel enhances telomeric silencing in Saccharomyces cerevisiae

Certain nickel compounds including crystalline nickel sulfide (NiS) and subsulfide (Ni3S2) are potent human and animal carcinogens. In Chinese hamster embryo cells, an X-linked senescence gene was inactivated following nickel-induced DNA methylation. Nickel also induced the inactivation of the gpt reporter gene by chromatin condensation and a DNA methylation process in a transgenic gpt+ Chinese hamster cell line (G12), which is located near a heterochromatic region. To determine if nickel can cause gene silencing independently of DNA methylation, based only on the induction of changes in chromatin structure, we measured its effect on gene silencing in Saccharomyces cerevisiae. Growth of yeast in the presence of nickel chloride repressed a telomeric marker gene (URA3) and resulted in a stable epigenetic switch. This phenomenon was dependent on the number of cell doubling prior to selection and also on the distance of the marker gene from the end of the chromosome. The level of TPE (telomeric position effect) increased linearly with elevations of nickel concentration. Addition of magnesium inhibited this effect, but magnesium did not silence the reporter gene by itself. The level of silencing was also assessed following treatment with other transition metals: cobalt, copper and cadmium. In the sublethal range, cobalt induced similar effects as nickel, while copper and cadmium did not change the basal level of gene expression. Silencing by copper and cadmium were evident only at concentrations of those metals where the viability was very low.     

Susceptibility to Heavy Metals and Cadmium Accumulation in Aerobic and Anaerobic Thermophilic Microorganisms Isolated from Deep-Sea Hydrothermal Vents

Thirty thermophilic strains isolated from heavy metal-rich hydrothermal vent sites at Lau Basin were tested for their susceptibility to cadmium, zinc, cobalt, and nickel. The 14 aerobic spore formers belonging to the genus Bacillus, 6 anaerobic fermenters from the order Thermotogales, and 10 anaerobic sulfur reducers from the order Thermococcales could be clearly distinguished according to their metal susceptibilities. The Thermococcales were found to exhibit the highest resistance to cadmium and zinc, whereas Thermotogales were highly sensitive to these metals. In contrast, the Thermotogales displayed the highest resistance to cobalt ions. No clear distinction could be established between the metal susceptibilities of these strains and seven reference organisms used for comparative studies. Cadmium resistance, slightly inducible in some cadmium-resistant bacilli, was not plasmid mediated. The amount of cadmium immobilized by the Thermotogales was related to their level of resistance to this metal. Received: 24 February 2000 / Accepted: 28 March 2000     

Metal‐responsive RNA polymerase extracytoplasmic function (ECF) sigma factors

In order to survive, bacteria must adapt to multiple fluctuations in their environment, including coping with changes in metal concentrations. Many metals are essential for viability, since they act as cofactors of indispensable enzymes. But on the other hand, they are potentially toxic because they generate reactive oxygen species or displace other metals from proteins, turning them inactive. This dual effect of metals forces cells to maintain homeostasis using a variety of systems to import and export them. These systems are usually inducible, and their expression is regulated by metal sensors and signal‐transduction mechanisms, one of which is mediated by extracytoplasmic function (ECF) sigma factors. In this review, we have focused on the metal‐responsive ECF sigma factors, several of which are activated by iron depletion (FecI, FpvI and PvdS), while others are activated by excess of metals such as nickel and cobalt (CnrH), copper (CarQ and CorE) or cadmium and zinc (CorE2). We focus particularly on their physiological roles, mechanisms of action and signal transduction pathways.     

Effect of nutrients supplementation on anaerobic sludge development and activity for treating distillery effluent

Startup of laboratory anaerobic reactors and treatment efficiency were investigated by supplementing the distillery effluent feed with macronutrients (Ca, P) and micronutrients (Ni, Fe and Co) under mesophilic conditions. Calcium and phosphate were deterimental to the treatment efficiency and sludge granulation. Traces of salts of iron, nickel and cobalt, individually and in combinations improved the COD removal efficiency and sludge granulation process.     

Metal complexes of the schiff bases 2-pyridinylhydrazine and 2-quinolinyl-hydrazine with 2-pyridinecarboxaldehyde N-oxide,including some N-oxide-bridged antiferromagnetic complexes of cobalt(II) and nickel(II)

Metal complexes of 2-pyridine carboxaldehyde 2′-pyridinylhydrazone 1-oxide (poph) and 2-pyridinecarboxaldehyde 2′-quinolinylhydrazone 1-oxide (poqh) are reported with copper(II), nickel(II), cobalt(II), iron(II) and manganese(II). Each ligand appears to function as an ONN donor, via the pyridine N-oxide oxygen, the imine nitrogen, and a pyridine or quinoline nitrogen. The complexes have been characterised by magnetic susceptibility measurements to liquid nitrogen temperature, and also by electronic, infrared, X-ray powder diffraction, and Mössbauer spectra. No magnetic interaction was detected with the copper(II) complexes. All the complexes of metal nitrates appear to be monomers.The complexes of poph with the halides and thiocyanates of nickel(II) and cobalt(II) appear to be six-coordinate and N-oxide-bridged; they exhibit varying degress of antiferromagnetic interaction and the magnetic data for the nickel(II) complexes have been fitted to various models. In contrast, the bulky ligand poqh produces halide-bridged six-coordinate nickel(II) complexes and monomeric five-coordinate cobalt(II) complexes.This behaviour by poqh resembles that of the related NNN ligands paphy and paqhy, which are the Schiff bases of 2-pyridinecarboxaldehyde with 2-pyridinylhydrazine and 2-quinolinylhydrazine, respectively.     

Nickel enhances telomeric silencing in Saccharomyces cerevisiae

Certain nickel compounds including crystalline nickel sulfide (NiS) and subsulfide (Ni₃S₂) are potent human and animal carcinogens. In Chinese hamster embryo cells, an X-linked senescence gene was inactivated following nickel-induced DNA methylation. Nickel also induced the inactivation of the gpt reporter gene by chromatin condensation and a DNA methylation process in a transgenic gpt+ Chinese hamster cell line (G12), which is located near a heterochromatic region. To determine if nickel can cause gene silencing independently of DNA methylation, based only on the induction of changes in chromatin structure, we measured its effect on gene silencing in Saccharomyces cerevisiae. Growth of yeast in the presence of nickel chloride repressed a telomeric marker gene (URA3) and resulted in a stable epigenetic switch. This phenomenon was dependent on the number of cell doubling prior to selection and also on the distance of the marker gene from the end of the chromosome. The level of TPE (telomeric position effect) increased linearly with elevations of nickel concentration. Addition of magnesium inhibited this effect, but magnesium did not silence the reporter gene by itself. The level of silencing was also assessed following treatment with other transition metals: cobalt, copper and cadmium. In the sublethal range, cobalt induced similar effects as nickel, while copper and cadmium did not change the basal level of gene expression. Silencing by copper and cadmium were evident only at concentrations of those metals where the viability was very low.     

大肠杆菌拓扑异构酶I结合重金属的特性及功能影响

【背景】大肠杆菌拓扑异构酶Ⅰ(Escherichia coli topoisomerase I,E.coli TopA)在DNA复制、转录、重组和基因表达调控等过程发挥关键作用。研究表明E.coli TopA只有结合锌离子才具有活性,然而E.coli TopA能否结合其他金属离子尤其是重金属离子,以及结合其他金属后是否具有活性,目前仍不清楚。【目的】探究大肠杆菌拓扑异构酶Ⅰ是否结合环境中常见重金属离子,研究重金属离子结合E.coli TopA蛋白后对其活性的影响。【方法】在分别添加有锌、钴、镍、镉、铁、汞、砷、铬、铅、铜离子的M9基础培养中表达、纯化出E.coli TopA蛋白,并对纯化得到的蛋白用电感耦合等离子体质谱仪进行相应金属离子含量的测定;利用表达E.coli TopA锌指结构的突变体蛋白鉴定重金属离子的结合位点;通过体外超螺旋DNA松弛实验测定不同金属结合E.coli TopA的拓扑异构酶活性;通过测定蛋白内源性荧光推测不同金属结合E.coli TopA的空间构象差异。【结果】E.coli TopA在体内除了能结合锌和铁之外,还能够结合钴、镍、镉3种离子,但是不能结合汞、砷、铬、铅、铜离子。钴、镍、镉结合形式的E.coli TopA,每个蛋白分子最多可以结合3个相应的金属离子,他们与TopA蛋白的结合位点也是位于3个锌指结构域,而且每个锌指结构域结合1个金属离子。此外,E.coli TopA结合钴、镍、镉离子后,其DNA拓扑异构酶活性并未受到影响,可能是由于钴、镍、镉离子结合形式的E.coli TopA蛋白,其空间构象与锌结合形式相比并未发生显著变化。【结论】由于DNA拓扑异构酶在维持细胞正常生理功能中发挥关键作用,研究表明E.coli TopA的功能不会受到常见重金属的干扰(不结合或者结合后活性无影响),这也有可能是大肠杆菌在进化过程中产生的对抗环境中重金属离子毒害作用的一种自我保护和耐受机制,具有重要的生理意义。