Cupriavidus Necator
   HOME

TheInfoList



OR:

''Cupriavidus necator'' is a
Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
of the class
Betaproteobacteria ''Betaproteobacteria'' are a class of Gram-negative bacteria, and one of the six classes of the phylum '' Pseudomonadota'' (synonym Proteobacteria). Metabolism The ''Betaproteobacteria'' comprise over 75 genera and 400 species. Together, they ...
.


Taxonomy

''Cupriavidus necator'' has gone through a series of name changes. In the first half of the 20th century, many micro-organisms were isolated for their ability to use hydrogen. Hydrogen-metabolizing chemolithotrophic organisms were clustered into the group ''Hydrogenomonas''. ''C. necator'' was originally named ''Hydrogenomonas eutrophus'' because it fell under the ''Hydrogenomonas'' classification and was "well nourished and robust". Some of the original ''H. eutrophus'' cultures isolated were by Bovell and Wilde. After characterizing cell morphology,
metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
and
GC content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out of ...
, the ''Hydrogenomonas'' nomenclature was disbanded because it comprised many species of microorganisms. ''H. eutrophus'' was then renamed ''Alcaligenes eutropha'' because it was a micro-organism with degenerated peritrichous
flagellation Flagellation (Latin , 'whip'), flogging or whipping is the act of beating the human body with special implements such as whips, Birching, rods, Switch (rod), switches, the cat o' nine tails, the sjambok, the knout, etc. Typically, floggin ...
. Investigating
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...
,
lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...
composition,
fatty acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...
composition and
16S rRNA 16S ribosomal RNA (or 16Svedberg, S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as ...
analysis, ''A. eutropha'' was found to belong to the genus ''Ralstonia'' and named ''Ralstonia eutropha''. Upon further study of the genus, ''Ralstonia'' was found to comprise two phenotypically distinct clusters. The new genus ''Wautersia'' was created from one of these clusters which included ''R. eutropha''. In turn ''R. eutropha'' was renamed ''Wautersia eutropha''. Looking at
DNA–DNA hybridization In genomics, DNA–DNA hybridization is a molecular biology technique that measures the degree of genetic similarity between DNA sequences. It is used to determine the genetic distance between two organisms and has been used extensively in phylo ...
and phenotype comparison with ''Cupriavidus necator'', ''W. eutropha'' was found to be the same species as previously described ''C. necator''. Because ''C. necator'' was named in 1987 far before the name change to ''R. eutropha'' and ''W. eutropha'', the name ''C. necator'' was assigned to ''R. eutropha'' according to Rule 23a of the
International Code of Nomenclature of Bacteria The International Code of Nomenclature of Prokaryotes (ICNP) or Prokaryotic Code, formerly the International Code of Nomenclature of Bacteria (ICNB) or Bacteriological Code (BC), governs the scientific names for Bacteria and Archaea.P. H. A. Sneath ...
.


Metabolism

''Cupriavidus necator'' is a hydrogen-oxidizing bacterium ("knallgas" bacterium) capable of growing at the interface of anaerobic and aerobic environments. It can easily adapt between
heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
ic and
autotroph An autotroph is an organism that can convert Abiotic component, abiotic sources of energy into energy stored in organic compounds, which can be used by Heterotroph, other organisms. Autotrophs produce complex organic compounds (such as carbohy ...
ic lifestyles. Both organic compounds and hydrogen can be used as a source of energy ''C. necator'' can perform
aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cellu ...
or
anaerobic respiration Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing ...
by
denitrification Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
of nitrate and/or nitrite to nitrogen gas. When growing under autotrophic conditions, ''C. necator'' fixes carbon through the reductive pentose phosphate pathway. It is known to produce and sequester
polyhydroxyalkanoate Polyhydroxyalkanoates or PHAs are polyesters produced in nature by numerous microorganisms, including through bacterial fermentation of sugars or lipids. When produced by bacteria they serve as both a source of energy and as a carbon store. More ...
(PHA) plastics when exposed to excess amounts of sugar substrate. PHA can accumulate to levels around 90% of the cell's dry weight. To better characterize the lifestyle of ''C. necator'', the
genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
s of two strains have been
sequenced In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succi ...
.


Hydrogenases

''Cupriavidus necator'' can use hydrogen gas as a source of energy when growing under autotrophic conditions. It contains four different
hydrogenase A hydrogenase is an enzyme that Catalysis, catalyses the reversible Redox, oxidation of molecular hydrogen (H2), as shown below: Hydrogen oxidation () is coupled to the reduction of electron acceptors such as oxygen, nitrate, Ferric, ferric i ...
s that have i-Feactive sites and all perform this reaction: :H2 \rightleftharpoons 2H+ + 2e The hydrogenases of ''C. necator'' are like other typical i-Fehydrogenases because they are made up of a large and a small subunit. The large subunit is where the i-Feactive site resides and the small subunit is composed of e-Sclusters. However, the hydrogenases of ''C. necator'' are different from typical i-Fehydrogenases because they are tolerant to oxygen and are not inhibited by CO. While the four hydrogenases perform the same reaction in the cell, each hydrogenase is linked to a different cellular process. The differences between the regulatory hydrogenase, membrane-bound hydrogenase, soluble hydrogenase and actinobacterial hydrogenase in ''C. necator'' are described below.


Regulatory hydrogenase

The first hydrogenase is a regulatory hydrogenase (RH) that signals to the cell hydrogen is present. The RH is a protein containing large and small i-Fehydrogenase subunits attached to a histidine protein kinase subunit. The hydrogen gas is oxidized at the i-Fecenter in the large subunit and in turn reduces the e-Sclusters in the small subunit. It is unknown whether the electrons are transferred from the e-Sclusters to the protein kinase domain. The histidine protein kinase activates a
response regulator In molecular biology, a response regulator is a protein that mediates a cell's response to changes in its environment as part of a two-component regulatory system. Response regulators are coupled to specific histidine kinases which serve as sens ...
. The response regulator is active in the dephosphorylated form. The dephosphorylated response regulator promotes the transcription of the membrane bound hydrogenase and soluble hydrogenase.


Membrane-bound hydrogenase

The membrane-bound hydrogenase (MBH) is linked to the
respiratory chain An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this ...
through a specific
cytochrome b Cytochrome b is a protein found in the membranes of aerobic cells. In eukaryotic mitochondria (inner membrane) and in aerobic prokaryotes, cytochrome b is a component of respiratory chain complex III () — also known as the bc1 complex or ubiq ...
-related protein in ''C. necator''. Hydrogen gas is oxidized at the i-Feactive site in the large subunit and the electrons are shuttled through the e-Sclusters in the small subunit to the cytochrome b-like protein. The MBH is located on the outer
cytoplasmic membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the cytoplasm, interior of a Cell (biology), cell from the extrac ...
. It recovers energy for the cell by funneling electrons into the respiratory chain and by increasing the
proton gradient An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts: * The chemical gradient, or difference in solute concentration across a membrane. ...
. The MBH in ''C. necator'' is not inhibited by CO and is tolerant to oxygen.


NAD+-reducing hydrogenase

The NAD+-reducing hydrogenase (soluble hydrogenase, SH) creates a
NADH Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an ade ...
-reducing equivalence by oxidizing hydrogen gas. The SH is a heterohexameric protein with two subunits making up the large and small subunits of the i-Fehydrogenase and the other two subunits comprising a reductase module similar to the one of
Complex I Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the respiratory chains of many organisms from bacteria to humans. It catalyzes th ...
. The i-Feactive site oxidized hydrogen gas which transfers electrons to a FMN-a cofactor, then to a e-Scluster relay of the small hydrogenase subunit and the reductase module, then to another FMN-b cofactor and finally to NAD+. The reducing equivalences are then used for fixing carbon dioxide when ''C. necator'' is growing autotrophically. The active site of the SH of ''C. necator'' H16 has been extensively studied because ''C. necator'' H16 can be produced in large amounts, can be genetically manipulated, and can be analyzed with
spectrographic In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system ...
techniques. However, no crystal structure is currently available for the ''C. necator'' H16 soluble hydrogenase in the presence of oxygen to determine the interactions of the active site with the rest of the protein.


Typical anaerobic i-Fehydrogenases

The i-Fehydrogenase from '' Desulfovibrio vulgaris'' and ''D. gigas'' have similar protein structures to each other and represent typical i-Fehydrogenases. The large subunit contains the i-Feactive site buried deep in the core of the protein and the small subunit contains e-Sclusters. The Ni atom is coordinated to the Desulfovibrio hydrogenase by 4
cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...
ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
s. Two of these same cysteine ligands also bridge the Fe of the i-Feactive site. The Fe atom also contains three ligands, one CO and two CN that complete the active site. These additional ligands might contribute to the reactivity or help stabilize the Fe atom in the low spin +2 oxidation state. Typical iFehydrogenases like those of ''D. vulgaris'' and ''D. gigas'' are poisoned by oxygen because an oxygen atom binds strongly to the NiFe active site.


''C. necator'' oxygen-tolerant SH

The SH in ''C. necator'' are unique for other organisms because it is oxygen tolerant. The active site of the SH has been studied to learn why this protein is tolerant to oxygen. A recent study showed that oxygen tolerance as implemented in the SH is based on a continuous catalytically driven detoxification of ef missing  The genes encoding this SH can be up-regulated under heterotrophic growth condition using glycerol in the growth media and this enables aerobic production and purification of the same enzyme.


Applications

The oxygen-tolerant hydrogenases of ''C. necator'' have been studied for diverse purposes. ''C. necator'' was studied as an attractive organism to help support life in space. It can fix carbon dioxide as a carbon source, use the
urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...
in urine as a nitrogen source, and use hydrogen as an energy source to create dense cultures that could be used as a source of protein.
Electrolysis of water Electrolysis of water is using electricity to Water splitting, split water into oxygen () and hydrogen () gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture ...
is one way of creating oxygenic atmosphere in space and ''C. necator'' was investigated to recycle the hydrogen produced during this process. Oxygen-tolerant hydrogenases are being used to investigate biofuels. Hydrogenases from ''C. necator'' have been used to coat electrode surfaces to create hydrogen
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
s tolerant to oxygen and carbon monoxide and to design hydrogen-producing light complexes. In addition, the hydrogenases from ''C. necator'' have been used to create hydrogen sensors. Genetically modified ''C. necator'' can produce
isobutanol Isobutanol (IUPAC nomenclature: 2-methylpropan-1-ol) is an organic compound with the formula (CH3)2CHCH2OH (sometimes represented as ''i''-BuOH). This colorless, flammable liquid with a characteristic smell is mainly used as a solvent either dir ...
from that can directly substitute or blend with
gasoline Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...
. The organism emits the isobutanol without having to be destroyed to obtain it.


Industrial uses

Researchers at UCLA have genetically modified a strain of the species ''C. necator'' (formerly known as ''R. eutropha'' H16) to produce isobutanol from CO2 feedstock using electricity produced by a solar cell. The project, funded by the U.S. Dept. of Energy, is a potential high energy-density
electrofuel Electrofuels, also known as e-fuels, are a class of synthetic fuels which function as drop-in replacement fuels for internal combustion engines. They are manufactured using captured carbon dioxide or carbon monoxide, together with Hydrogen fuel, ...
that could use existing infrastructure to replace oil as a transportation fuel. Chemical and biomolecular engineers at
Korea Advanced Institute of Science and Technology KAIST (originally the Korea Advanced Institute of Science and Technology) is a national university, national research university located in Daedeok Innopolis, Daejeon, South Korea. KAIST was established by the Korean government in 1971 as the ...
has presented a scalable way to convert in the air into a
polyester Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include some natura ...
by means of the ''C. necator''.


References


External links


Type strain of ''Cupriavidus necator'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q148753 Burkholderiaceae Bacteria described in 1969 Formatotrophs