Hydrogenlyases: Further experiments on the formation of formic hydrogenlyase by Bact. coli

A paean to the ineffable Marjory Stephenson

It is now 75 years since Marjory Stephenson became the second President of the Society for General Microbiology (SGM). Around the time of her death at the end of 1948 many articles appeared extolling Marjory Stephenson’s contribution to the fields of Biochemistry and Microbiology. Not that much has been written about her since that time, which is unfortunate. Therefore, this brief review is intended as a form of redress and aims to highlight the role of this remarkable scientist in establishing the Society and in promoting Microbiology as a discipline. Notwithstanding the significance of these achievements, however, it is her overall impact on the field of ‘Chemical Microbiology’ and what she achieved through her research that are extraordinary, even by today’s standards. Marjory Stephenson recognized that in order to understand a biological system, the ‘whole’ organism must be considered and this can only be achieved by adopting an interdisciplinary approach: inorganic and organic chemistry, biochemistry, genetics, metabolism and ultimately physiology. Her scientific ethos serves today as a beacon for how scientific research should be conducted, and what we as scientists can learn about how to inspire and mentor the next generation. It is impossible to overstate Marjory Stephenson’s scientific legacy, or her overall contribution to Microbiology.

Molecular Hydrogen Metabolism: a Widespread Trait of Pathogenic Bacteria and Protists

Pathogenic microorganisms use various mechanisms to conserve energy in host tissues and environmental reservoirs. One widespread but often overlooked means of energy conservation is through the consumption or production of molecular hydrogen (H2). Here, we comprehensively review the distribution, biochemistry, and physiology of H2 metabolism in pathogens. Over 200 pathogens and pathobionts carry genes for hydrogenases, the enzymes responsible for H2 oxidation and/or production. Furthermore, at least 46 of these species have been experimentally shown to consume or produce H2 Several major human pathogens use the large amounts of H2 produced by colonic microbiota as an energy source for aerobic or anaerobic respiration. This process has been shown to be critical for growth and virulence of the gastrointestinal bacteria Salmonella enterica serovar Typhimurium, Campylobacter jejuni, Campylobacter concisus, and Helicobacter pylori (including carcinogenic strains). H2 oxidation is generally a facultative trait controlled by central regulators in response to energy and oxidant availability. Other bacterial and protist pathogens produce H2 as a diffusible end product of fermentation processes. These include facultative anaerobes such as Escherichia coli, S Typhimurium, and Giardia intestinalis, which persist by fermentation when limited for respiratory electron acceptors, as well as obligate anaerobes, such as Clostridium perfringens, Clostridioides difficile, and Trichomonas vaginalis, that produce large amounts of H2 during growth. Overall, there is a rich literature on hydrogenases in growth, survival, and virulence in some pathogens. However, we lack a detailed understanding of H2 metabolism in most pathogens, especially obligately anaerobic bacteria, as well as a holistic understanding of gastrointestinal H2 transactions overall. Based on these findings, we also evaluate H2 metabolism as a possible target for drug development or other therapies.

Formate hydrogenlyase: A group 4 [NiFe]-hydrogenase in tandem with a formate dehydrogenase

Hydrogenase enzymes are currently under the international research spotlight due to emphasis on biologically produced hydrogen as one potential energy carrier to relinquish the requirement for 'fossil fuel' derived energy. Three major classes of hydrogenase exist in microbes all able to catalyze the reversible oxidation of dihydrogen to protons and electrons. These classes are defined by their active site metal content: [NiFe]-; [FeFe]- and [Fe]-hydrogenases. Of these the [NiFe]-hydrogenases have links to ancient forms of metabolism, utilizing hydrogen as the original source of reductant on Earth. This review progresses to highlight the Group 4 [NiFe]-hydrogenase enzymes that preferentially generate hydrogen exploiting various partner enzymes or ferredoxin, while in some cases translocating ions across biological membranes. Specific focus is paid to Group 4A, the Formate hydrogenlyase complexes. These are the combination of a six or nine subunit [NiFe]-hydrogenase with a soluble formate dehydrogenase to derived electrons from formate oxidation for proton reduction. The incidence, physiology, structure and biotechnological application of these complexes will be explored with attention on Escherichia coli Formate Hydrogenlyase-1 (FHL-1).

The Model [NiFe]-Hydrogenases of Escherichia coli

In Escherichia coli, hydrogen metabolism plays a prominent role in anaerobic physiology. The genome contains the capability to produce and assemble up to four [NiFe]-hydrogenases, each of which are known, or predicted, to contribute to different aspects of cellular metabolism. In recent years, there have been major advances in the understanding of the structure, function, and roles of the E. coli [NiFe]-hydrogenases. The membrane-bound, periplasmically oriented, respiratory Hyd-1 isoenzyme has become one of the most important paradigm systems for understanding an important class of oxygen-tolerant enzymes, as well as providing key information on the mechanism of hydrogen activation per se. The membrane-bound, periplasmically oriented, Hyd-2 isoenzyme has emerged as an unusual, bidirectional redox valve able to link hydrogen oxidation to quinone reduction during anaerobic respiration, or to allow disposal of excess reducing equivalents as hydrogen gas. The membrane-bound, cytoplasmically oriented, Hyd-3 isoenzyme is part of the formate hydrogenlyase complex, which acts to detoxify excess formic acid under anaerobic fermentative conditions and is geared towards hydrogen production under those conditions. Sequence identity between some Hyd-3 subunits and those of the respiratory NADH dehydrogenases has led to hypotheses that the activity of this isoenzyme may be tightly coupled to the formation of transmembrane ion gradients. Finally, the E. coli genome encodes a homologue of Hyd-3, termed Hyd-4, however strong evidence for a physiological role for E. coli Hyd-4 remains elusive. In this review, the versatile hydrogen metabolism of E. coli will be discussed and the roles and potential applications of the spectrum of different types of [NiFe]-hydrogenases available will be explored.

Formate production through carbon dioxide hydrogenation with recombinant whole cell biocatalysts

The biological conversion of CO2 and H2 into formate offers a sustainable route to a valuable commodity chemical through CO2 fixation, and a chemical form of hydrogen fuel storage. Here we report the first example of CO2 hydrogenation utilising engineered whole-cell biocatalysts. Escherichia coli JM109(DE3) cells transformed for overexpression of either native formate dehydrogenase (FDH), the FDH from Clostridium carboxidivorans, or genes from Pyrococcus furiosus and Methanobacterium thermoformicicum predicted to express FDH based on their similarity to known FDH genes were all able to produce levels of formate well above the background, when presented with H2 and CO2, the latter in the form of bicarbonate. In the case of the FDH from P. furiosus the yield was highest, reaching more than 1 g L(-1)h(-1) when a hydrogen-sparging reactor design was used.

INCREASE IN BACTERIOPHAGE AND GELATINASE CONCENTRATION IN CULTURES OF BACILLUS MEGATHERIUM

1. The increase in bacteria, phage concentration, and gelatinase concentration in cultures of B. megatherium has been determined. 2. With lysogenic cultures the phage concentration, gelatinase concentration, and bacteria concentration increase logarithmically at first. The phage and gelatinase concentration then decrease while the bacteria concentration increases to a maximum. 3. The results are the same with sensitive cultures if the ratio of phage to bacteria is small. If the ratio of phage to bacteria is large phage, gelatinase, and bacteria concentration all increase at first and then decrease. The maximum rate of increase coincides approximately with the maximum rate of oxygen consumption of the culture. 4. 60–90 per cent of the phage is free from the cells. 5. The amount of phage produced is determined by the combined phage and not by the total phage. 6. Phage is produced during growth of the cells and not during lysis. 7. In a very narrow range of pH near 5.55 no increase in bacteria occurs but large increases in phage may be obtained.

The formation and stabilization of an adaptive enzyme in the absence of its substrate

It is shown that various substrates accelerate the disappearance of an adaptive enzyme when its own substrate has been removed from the medium. The order of effectiveness of such substrates appears to be connected with their chemical similarity to the adaptive substrate. It is shown that two conditions which are able to inhibit the formation of adaptive enzymes-anaerobiosis and the presence of sodium azide-are equally able to prevent the disappearance of an adaptive enzyme after the removal of its substrate. Finally, it is shown that rapidly growing cultures, under optimal conditions for synthetic activity, are able to maintain and even appreciably to increase their initial content of an adaptive enzyme, in the absence of its specific substrate and in the presence of a normally competitive substrate. In the light of these results, the three major theories of enzyme formation hitherto proposed are evaluated.

Glycine and formic hydrogenlyase

1. A strain of Boot, coli adapted to growth in high glycine concentrations, which had lost the power of producing ‘gas’ from sugars, was shown to be devoid of formic hydrogenlyase.

2. Formic acid was prominent among the products of fermentation of sugars by this strain.

3. The appearance of formic hydrogenlyase in vitro, in bacteria grown in such a way as not to contain the enzyme, was inhibited by glycine at high concentrations.

One of us (J. G.) is indebted to the Medical Research Council for a grant-in-aid for expenses.

Biochemistry of methanogenesis: a tribute to Marjory Stephenson. 1998 Marjory Stephenson Prize Lecture

Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, and Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, Karl-von-Frisch-Straße, D-35032 Marburg, Germany

In 1933, Stephenson & Stickland (1933a) published that they had isolated from river mud, by the single cell technique, a methanogenic organism capable of growth in an inorganic medium with formate as the sole carbon source.

Microbial production of hydrogen: an overview

Production of hydrogen by anaerobes, facultative anaerobes, aerobes, methylotrophs, and photosynthetic bacteria is possible. Anaerobic Clostridia are potential producers and immobilized C. butyricum produces 2 mol H2/mol glucose at 50% efficiency. Spontaneous production of H2 from formate and glucose by immobilized Escherichia coli showed 100% and 60% efficiencies, respectively. Enterobactericiae produces H2 at similar efficiency from different monosaccharides during growth. Among methylotrophs, methanogenes, rumen bacteria, and thermophilic archae, Ruminococcus albus, is promising (2.37 mol/mol glucose). Immobilized aerobic Bacillus licheniformis optimally produces 0.7 mol H2/mol glucose. Photosynthetic Rhodospirillum rubrum produces 4, 7, and 6 mol of H2 from acetate, succinate, and malate, respectively. Excellent productivity (6.2 mol H2/mol glucose) by co-cultures of Cellulomonas with a hydrogenase uptake (Hup) mutant of R. capsulata on cellulose was found. Cyanobacteria, viz., Anabaena, Synechococcus, and Oscillatoria sp., have been studied for photoproduction of H2. Immobilized A. cylindrica produces H2 (20 ml/g dry wt/h) continually for 1 year. Increased H2 productivity was found for Hup mutant of A. variabilis. Synechococcus sp. has a high potential for H2 production in fermentors and outdoor cultures. Simultaneous productions of oxychemicals and H2 by Klebseilla sp. and by enzymatic methods were also attempted. The fate of H2 biotechnology is presumed to be dictated by the stock of fossil fuel and state of pollution in future.

Induced Biosynthesis of Formic Hydrogenlyase in Iron-Deficient Cells of Escherichia coli

Fukuyama, T. (University of Washington, Seattle), and E. J. Ordal. Induced biosynthesis of formic hydrogenlyase in iron-deficient cells of Escherichia coli. J. Bacteriol. 90:673-680. 1965.-Escherichia coli cells were grown aerobically on a lactate-mineral salts medium from which iron had been removed by extraction with 8-hydroxyquinoline and chloroform. These cells carried out induced biosynthesis of formic hydrogenlyase in a reaction mixture containing glucose, formate, and phosphate without the addition of amino acids, providing adequate amounts of iron salts were present. In the absence of iron, glucose was fermented and acids were produced, but no formic hydrogenlyase developed. When iron-deficient E. coli cells were repeatedly washed, the property of carrying out induced biosynthesis of formic hydrogenlyase with glucose, formate, phosphate, and iron was lost, but was restored on addition of acid-hydrolyzed casein to the reaction mixture. An energy source (provided as glucose) was necessary for enzyme production. Iron-deficient cells were devoid of hydrogenase and formic hydrogenlyase but showed formic dehydrogenase activity when adequate amounts of selenium and molybdenum were present in the growth medium. Hydrogenase was consistently absent in iron-deficient cells but appeared concomitantly with formic hydrogenlyase during induced biosynthesis of the latter in iron-deficient cells of E. coli.

Marjory Stephenson, 1885-1948

Images