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The catholyte required a higher flow rate likely due to the continuous evaporation of liquid from the open-cathode chamber. Several MFC studies have tested a range of operation temperatures and demonstrated consistently higher power densities with higher temperatures, within the limits of the microbial pop- ulations Choi ; Moon et al. Carver et al. The MFC utilized an anaerobic, glass reactor design in combination with a cathode chamber submersed in anolyte.

Rather than having an extensive layers of gaskets, membrane, carbon paper, and polycarbonate as in the previous design Min and Angeladaki , the cathode chamber had a single-rubber O-ring that is able to prevent liquid or air crossover. The components of the cathode assembly, including the stainless screws, foil and graphite disks, have all been shown to be conducive and were securely connected.

Analyses of the glucose-fed thermophilic MFC showed improved performance over h with an increased maximum power of 3. The polari- zation curve has three distinct sections of irreversible voltage losses: activation loss, ohmic loss, and mass transfer loss.

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The typical initial and drastic voltage drop was not apparent, indicating lower than normal activation losses Carver et al. This is attributed to increased reaction rates at thermophilic temperatures that lowered the activation energy and therefore the voltage necessary to maintain active, anaerobic metabolism. Ohmic loss can be observed in the center of the polarization curve with the gradual decrease of voltage as current density increases Carver et al.

The slope of this overpotential section, equivalent to voltage over current, yielded an internal resistance of 9. This value is in the general range reported for other MFCs, although the experimental conditions are not comparable among the studies reviewed in the literature He et al. The results suggest the potential for stable, thermophilic MFC operation although optimization of biological and engineering components is necessary prior to application of the design. Even though the Pt-based cathode demonstrates high electrochemical activity, the use of Pt is undesirable due to high costs and easy inhibition by CO Logan ; Herrmann et al.

Even at small concentrations, CO can fully cover the Pt surface, thereby reducing the reaction site. CO is easily able to absorb to Pt due to the negative free energy of adsorption Baschuk and Li A maximum power density of 6. However, the high impeller speeds require a high-power input Henstra et al. As a solution, a bubble-free gas transfer to liquid has been accomplished by the selection of a membrane system with a high selectivity for the gaseous substrate.

Silicone membranes have also been used. These are dense membranes, which offer the advantage of high mechanical strength, flexibility, and stability under high temperature and pressures. Other promising alternatives to the conventional STRs for increased gas—liquid mass transfer include monolith packing and columnar reactors. Monolith packing consists of a number of narrow, straight, and parallel flow channels with a large-open frontal area which allows for a low flow resistance, leading to low pressure drops and low energy losses.

Similarly, columnar reactors such as bubble column, trickle bed, and airlift reactors offer the advantage of a high gas—liquid mass transfer rate with low operational and maintenance costs. Biomass consists of cellu- lose, hemicellulose, and lignin, and the latter of which is extremely resistant to degradation.

These pre-treatments are designed to allow the carbohydrate portion of the biomass to be broken down into simple sugars, for example, by enzymatic hydrolysis using exogenously added cellulases to release fermentable sugars Carere et al. Such approaches have been found to be expensive and rate-limiting Datar et al. Alternatively, processes using cellulolytic microorganisms Cl.

Biomass is available on a renewable basis, either through natural processes or anthropogenic activities e. It has been estimated that out of a global energy potential from modern biomass of EJ per year in , only 9 EJ 3. The use of existing waste streams such as municipal organic waste also differentiates itself from other feedstocks such as dedicated energy crops because these wastes are available today at economically attractive prices, and they are often already aggregated and require less indirect land use. Tapping into these sources using microbial fermentation process essentially con- verts existing toxic waste gas streams into valuable commodities such as biofuels.

The overall process of gas fermentation is outlined in Fig. CO ethanol , Liu et al. Due to petroleum products shortage during World War II, this technology flourished in some European countries providing fuel for both civilians and militaries Dasappa et al. More recently, in the s and s, synthesis gas was successfully used in the USA and Europe for heat and electricity Faaij This idea is not new and has been developed in the past few decades Wilhelm et al. Nevertheless, these are expensive processes subjected to high pressures and temperatures Takeguchi et al. Some synthesis gas transformations to biofuels such as ethanol, butanol, and hydrogen can be performed using chemical as well as bio- logical catalysts Fig.

Production of biofuel from syngas is either performed using inorganic or metal-based catalysts known as Fischer—Tropsch FT process or microbial catalysts known as syngas fermentation Mohammadi et al. The CO and H2 present in syngas are substrates for microbial metabolism, which can be exploited for the synthesis of various interesting products. It is expected that syngas fermentation will play a role in the conversion of biomass, wastes, and residues that form poor substrates for direct fermentation.

Since then, microbial fermentation of syngas produced from cellulosic materials has been studied by many and has even been demonstrated in full-scale operation. Although most strains showed the formation of acetate, formate, butyrate, ethanol, and butanol were also reported as products. Additionally, several purple non-sulfur bacteria were isolated that are able to convert CO to H2 in a process similar to the WGS reaction Table 4. These include the homoacetogens acetogenic microorganisms that produce acetate as major fermentation product Table 4.

Mesophilic Carboxydotrophs that Produce Acetate Eubaterium limosum isolated from various environments, e. Other homoacetogens, including Clostridium aceticum Wieringa , and Acetobacterium woodii Balch et al. In , spores of the original strain were serendipitously found and reactivated Braun et al. Acetate is produced from growth-supporting substrates including H2, CO2, CO, and a range of sugars fructose, ribose, glutamate, fumarate, malate, and pyruvate.

With fructose, small amounts of ethanol have been reported under certain conditions Buschhorn et al. Recently, the genome of A. Most recently published research on A. Other thermophiles, such as M. Moorella thermoacetica is considered a model acetogen Drake and Daniel and it was used by Wood and Ljungdahl Wood and later by Ragsdale and Pierce to elucidate the Wood—Ljungdahl pathway. Over the past 10 years, new Moorella strains have been isolated and explored for both acetate and ethanol production, although only very low ethanol productivities have been reported Balk et al.

Due to its role in the elucidation of the Wood—Ljungdahl pathway, M. In , M. Archaeoglobus fulgidus is a strict anaerobic hyperthermophilic archaeon that oxidizes lactate completely to CO2 with sulfate as electron acceptor Stetter The genome sequence of A. In the presence of CO and sulfate, the culture OD increased to 0. Accumulation of formate was transient. Hydrogen was never detected. Under the conditions tested, the observed concentrations of acetate 18 mM and formate 8.

Methylviologen-dependent formate dehydrogenase FDH activity 1. It is speculated that formate formation proceeds through hydrolysis of formyl-methanofuran or form- yltetrahydromethanopterin. Moorella thermoautotrophica, previously known as C. No supple- mental amino acids were required for growth of the adapted strain, and nicotinic acid was the sole essential vitamin. Neither N2 nor nitrate could replace ammonium as the nitrogen source, and biotin was preferentially stimulatory for glucose cell lines.

Another Moorella strain that produce acetate is Moorella stamsii. This strain was isolated from anaerobic sludge from a municipal solid waste digester Alves et al. The pH range for growth is between 5. In addition, the isolate was able to grow with CO as the sole carbon and energy source. CO oxidation was coupled to H2 and CO2 formation.

Desulfotomaculum kuznetsovii and D. The co-cultures of C. When C. At the end of the experiment, 4. Under shaken conditions, H2 accumu- lates rapidly, and its further conversion occurs slowly. Sulfate reduction is inhibited only 0. More acetate 6. Under shaken conditions, H2 is formed fast, but only after all CO is converted, the H2 concen- tration decreased and SO4 is reduced Pashina et al. Acetate concentration is 4 mM in standing cultures and 7. Thermoanaerobacter kivui formerly A. The original genus Acetogenium was named because organism principally produces acetic acid from substrates Leigh et al.

Although ethanol production from synthesis gas was detected, the main product was acetate. Klasson et al. This increased both ethanol and cell concentrations. Adding reducing agents to the media seemed to alter electron flow to NADH formation and, in turn, increased ethanol production. Investigations also showed that C. It is able to grow and uptake CO and H2 in the presence of up to 2. This is relevant since syngas contains a considerable amount of these gases.

This organism favors the production of acetate during its active growth phase, while ethanol is produced primarily as a non-growth-related product Klasson The production of acetate is favored at higher pH 5—7 , whereas the production of ethanol is favored at lower values pH 4—4. A few years after C.

It is also capable of using CO2 and H2, as well as organic compounds such as pyruvate, xylose, arabinose, fructose, rhamnose, and L-glutamate as sub- strates Abrini Minimal research was done on C. Only low-level ethanol production of 0. It was found to produce acetate, ethanol, butyrate, and butanol from CO to H2 Liou et al. It is motile, Gram-positive, and spore-forming and forms acetate, ethanol, butyrate, and butanol as end products. The optimum pH range for this strain is 5. Currently, the most attractive syngas fermentation process is using C.

Clostridium ragsdalei or strain P11 was isolated from duck pond sediment by researchers from The University of Oklahoma and Oklahoma State University and is described in a patent Huhnke et al. In a L STR, an ethanol concentration of This was notably carried out at an initial pH between 7. Thermophilic Carboxydotrophs that Produce Ethanol Moorella sp. HUC is a thermophilic microorganism capable of producing ethanol from synthesis gas Sakai et al.

Even when the pH and the cell recycle were lowered, the ethanol production was improved only fold 1—15 mM and an ethanol:acetate molar ratio of Sakai et al. Aldh was shown to catalyze the thioester cleavage of acetyl-CoA, as well as the thioester condensation from CoASH and acetaldehyde.

This enzyme can also use NAD H as a cofactor but with decreased activity. AdhC showed no activity with any of the cofactors used. Surprisingly, the highest activities were toward n-butylaldehyde and isobutylalde- hyde, even though this organism has not been shown to produce butanol. Butyribacterium methylotrophicum is a catabolically versatile spore-forming anaerobe Zeikus et al.

It also possesses the advantageous ability to produce butanol from synthesis gas Grethlein et al. It is one of the most versatile CO-utilizing bacteria Grethlein et al. Other fermentation products are eth- anol, acetate, and butyrate. Notably, growth on high CO more than kPa, 1 atm concentrations and the production of butyrate and butanol from CO were dependent on the selection of a CO-adapted strain.

After some changes in fermentation setup, such as operation at pH 5. Another interesting, but less studied, strain for butanol production is C. Being able to produce up to four times more ethanol than butanol from CO or producer gas, this strain has mostly been studied for its ethanol production capabilities Datar et al. Products include acetate, ethanol, butanol, and butyrate. Draft genome sequences are available for C. Bruant et al. The two-carbon acetyl segment of acetyl-CoA is con- verted to the four carbon butyryl-CoA through thiolase, 3-hydroxybutyryl-CoA dehydrogenase, crotonase, and butyryl-CoA dehydrogenase as in ABE fermentation organism C.

Clostridium drakei was isolated from an acidic coal mine pond Liou et al. Thermophilic Carboxydotrophs that Produce Butanol Nguyen et al. To assess the biochemical basis for their ability to produce butanol from CO, CODH and butanol dehydrogenase activities were assessed for each of the isolates. All isolates showed evidence of CODH and BDH enzyme activities, with the majority exhibiting higher activities compared with the known carboxydotroph, B. Even though several anaerobic carboxydotrophs have been isolated with the ability to convert synthesis gas to biofuels, they are predominantly mes- ophilic Table 4.

So far, very few attempts have been made to isolate thermo- philic microorganisms that can produce organic compounds from syngas. Growth temperatures by thermophiles at high temperatures could be advantageous as less cooling of the syngas is required before it is introduce into the bioreactor. More- over, higher temperatures can lead to higher conversion rates, although higher temperatures do have a negative impact on the solubility of CO and H2 Henstra et al.

Rhodospirillum rubrum, Rhodopseudomonas palustris P4, Citrobacter sp. The former catalyzes the oxidation of CO, and hydrogenase mediates the reduction of protons to H2 Maness et al. Therefore, minimum energy requirements and low process cost are expected Ismail et al. Rhodospirillum rubrum grows quickly and reaches high cell concentrations that uptake CO more rapidly than other similar organisms capable of performing the GWS reaction Klasson et al.

It also tolerates small amounts of O2 and sulfur often present in syngas Klasson et al. As a result, this strain is the favorite organism for studies investigating biohydrogen production from syngas.

Introduction

This type of bioreactor was stable for continuous operation for 27 days Ismail et al. Rubrivivaxgelatinosus CBS is another promising strain for its use in syngas-to- hydrogen conversion. Its tolerance for oxygen Maness and Weaver and its capacity to use CO as the sole carbon and energy source Markov and Weaver make it an attractive biocatalyst. All isolated species are capable of chemolithotrophic growth on CO. So far, there exists no evidence of growth inhibition by high levels of CO.

Some isolates also grow by fermentation or anaerobic respiration. Because of simultaneous H2 production and acceptor reduction, it is unknown whether CO is a direct electron donor in anaerobic res- piration or H2 acts as an intermediate. Later it was found capable to ferment pyruvate to acetate Svetlichnyi et al. Caldanaerobacterium subterraneus subsp. It was isolated from a submarine hydrothermal vent. Besides CO, it also grows organotrophically on several mono- and disaccharides, cellulose, and starch.

The reductive acetyl-CoA pathway is not cyclic like the Calvin cycle or the reverse TCA cycle in that it is formed by two branches Fig. These branches have been called the Eastern or carbonyl and Western or methyl branches and were the research focus of Lars Ljungdahl and Harland Wood, respectively Ragsdale The Eastern branch produces the methyl group of acetyl-CoA, and the Western produces the carbonyl group. The methyl group is formed from the reduction of CO2 to formate which is converted to formyltetrahydrofolate and is reduced to methyltetrahydrofolate. These steps involve FDH and a series of tetrahydrofolate-dependent enzymes Drake CODH is the central enzyme in this pathway Wood et al.

In chemolithoautotrophs, this enzyme also enables the uti- lization of CO as the sole carbon and electron source by catalyzing the oxidation of CO to CO2. In these organisms, energy is conserved through an ETC. In hydrog- enogenic carboxydotrophs, the CODH reaction is the same as chemolithoauto- trophs. However, the electrons are transferred to a membrane-associated hydrogenase that combines the generation of hydrogen with the translocation of protons. Energy in this system is also generated through an ETC.

There has even been found a hyperthermophilic bacterium, C. The Wood—Ljungdahl pathway Fig. CO enters the pathway through two routes. This depends if CO serves as both carbon and energy source, or if an additional energy source such as hydrogen is present which can be utilized in a hydrogenase reaction Fig. The electron production is thermodynamically more favorable from CO than from H2 Hu et al.

Thus, at high CO concentrations, no or only little hydrogen uptake will occur, but it will increase, once CO is utilized and the concentration drops. Ethanol and acetate can be produced according to the following reactions: with CO as the sole carbon an energy source, as in Eqs. The genes encoding the enzymes that operate in the Eastern branch are ubiquitous and in M.

The Western or carbonyl branch Fig. CO can either be used directly, or generated from CO2, and serves as the carbonyl group for acetyl-CoA synthesis. Bacteria and archaea have slightly different acetyl-CoA pathway. For Archaea, a methanofuran-bound formyl reduced from CO2 is converted to tetrahydrometha- nopterin. Because the formation of acetyl-CoA from H2 and CO2 requires energy, acetate is transferred from acetyl-CoA to recover the lost energy from the formation of acetyl-CoA.

Ethanol is produced from the further reduction of acetate.

Two acetyl-CoA molecules yield an acetoacetyl-CoA which further produces butanol and butyrate Henstra et al. Hydrogen production from syngas is metabolized by hydrogenogenic carbo- xydotrophs Fig. Energy-converting hydrogenase ECH receives electrons and reduces protons to yield hydrogen Hedderich ; Singer et al. Used as a starting material for vinyl acetate and acetic anhydride synthesis Wagner , demand for acetic acid has grown over the past decade and is expected to reach Three organisms have been used for acetate or calcium—magnesium—acetate CMA production: C.

While acetic acid has no potential as fuel, some organisms such as oleaginous yeasts are able to convert acetic acid and other volatile fatty acids VFAs into lipids, which could be used as biodiesel Fei et al. An acetogen converts CO2 to acetate, which is then used by oleaginous yeast to produce lipids with CO2 as a by-product which could then be fed back to the acetogen. The reducing power can either come from H2 or electricity.

Most of this ethanol is produced by microbial fermentation of sugars from either sugarcane or corn starch. To make ethanol a commercial fuel contender, the feedstock has to be switched to lignocellulosic biomass. Hydroly- sis—fermentation technology has proven to be expensive and labor-intensive. Moreover, ethanol produced this way has not been able to compete with fossil fuel derivatives such as gasoline and diesel.

In , C. The syngas fermentation into ethanol and other bioproducts is considered to be more attractive due to several inherent merits over the biochemical approach and the Fisher—Tropsch FT process Bredwell et al. Ethanol is the most desirable product in biomass-derived syngas fermentation Schmidt et al. Younesi et al. Under normal growth conditions, the wild-type strain of C.

Several studies focused on improving the ethanol yield in Clostridia through the addition of a reducing agent, the supplementation of additional media constituents, pH shifts, the addition of hydrogen, and providing nutrient-limiting conditions. A condition that induces sporulation has also been found to favor solventogenesis Klasson et al.

Maximum product and cell yields obtained from different studies are summarized in Table 4. Butanol has a number of notable qualities that make it a suitable alter- native fuel. Reports of biological butanol formation date back to Louis Pasteur. Acetone was needed to prepare munitions, and it was in great shortage at the time.

Thus, it alleviates some of the problems asso- ciated with the utilization of lignocellulosic biomass. One of the most critical problems in ABE fermentation is solvent toxicity. The lipophilic solvent butanol is more toxic than others as it disrupts the phos- pholipid components of the cell membrane causing an increase in membrane flu- idity Bowles and Ellefson Moreira et al. They found that 0. Increased membrane fluidity causes destabilization of the membrane and disruption of membrane-associated functions such as various transport processes, glucose uptake, and membrane- bound ATPase activity Bowles and Ellefson Also, butanol is the only solvent produced to the level that becomes toxic to the cells during the fermentation of clostridia Jones and Woods To develop economical and sustainable processes for biobased butanol pro- duction, the metabolic pathways of native producers, such as clostridia, need to be well characterized and optimally redesigned.

However, much improvement is still needed to make an economically competitive process for biobased butanol production. Based on the genome sequence, a genome-scale metabolic model has been successfully reconstructed. Hydrogen introduces no new carbon to the atmosphere and produces no harmful by-products. Thus, hydrogen is considered to be a clean fuel since water is the only by-product when it is burned. Burning hydrogen not only has the potential to meet a wide variety of end-use applications but also does not contribute to greenhouse emission, acid rain, or ozone depletion Kotay and Das Hydrogen can be used either as the fuel for direct combustion in an internal combustion engine or as the fuel for a fuel cell.

It has a wide variety of applica- tions, including fuel for automobiles, distributed and central electricity and thermal energy generation Fig. Although hydrogen is the most abundant element in the universe, it must be produced from other hydrogen- containing compounds such as fossil fuels, biomass, or water. Each method of production requires a source of energy, i. Natural gas and coal SMR are the least expensive known technologies for H2 production.

This process results in a gas mixture of mainly CO and H2. Syngas may also be converted to hydrogen via the WGS reaction. Future research will likely address these issues. Several hydrogenogenic carboxydortrophs belonging to the genera Citrobacter, Peptostreptococcus, Rubrivivax, Rhodo- pseudomonas, R. Research progress for identifying the major technoeconomic bottlenecks of various bioprocesses for commercial production of hydrogen appears promising.

However, high hydrogen yield remains to be the ultimate goal and challenge for the biohydrogen research and development. While a portion of the excess heat can be converted into elec- tricity, some of the heat is also lost to the surroundings. This would greatly reduce the amount of heat that is lost in the process Henstra et al. In order to maximize syngas conversion, the mass transfer rate must be optimized.

In the experiment by Younesi et al. Both these factors increased the mass transfer rate. In the experiment, R. The agitation speed and gas flow rates were varied in order to determine their effects on the mass transfer rate. At low agitation speeds, little carbon monoxide was converted due to the low mixing of reactants. However, when agitation speeds were raised above rpm, the nutrients became toxic due to foaming of the mixture.

However, when high gas rates were used, some of the carbon monoxide passed through the reactor too quickly and was not converted.


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For the experiment by Younesi et al. Gas—liquid mass transfer is a rate-limiting step in syngas fermentation process Worden et al. Mass transfer limitations are inevitable at several points of the diffusion process including the transport of gaseous substrate into gas—liquid interface, its transport into culture media aqueous phase , the transport of the mixed gases into the stagnant liquid layer around the microbes, and the diffusion of the transported gaseous substrate into the microbial cell. The gas—liquid interface mass transfer is the major resistance for gaseous substrate diffusion.

Diffusion limitations of a gaseous substrate into the culture media result in low substrate uptake by microbes and thus lead to low productivity Munasinghe and Khanal Thus, reactor design plays an important role in syngas fer- mentation. Similarly, the bioreactor size greatly depends on the rate of mass transfer for sparingly soluble gases Vega et al.

Recently, metabolic engineering and synthetic biology techniques have been applied to gas fermentation organisms. This work strives to improve microbial productivity and robustness and to introduce pathways for the commercial production of increasingly energy dense fuels and more valuable chemicals. Over the past two decades, genetic techniques for clos- tridia, such as antisense RNA strategies Desai et al. More recently, integration-based techniques such as ClosTron Heap et al. Until the last 5 years, there was a notable lack of tech- niques and tools allowing chromosomal manipulation in gas fermentation organ- isms.

Throughout the literature, many microorganisms have been genetically manipulated for enhanced biofuel production. However, synthesis gas has not been the source of energy or growth for organisms in these experiments.

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This is probably due to the lack of genetic information and tools for syngas utilizing organisms. The work of Nishio and colleagues Inokuma et al. Metabolic engineering of these microorganisms may further facilitate biomass conversion to biofuels as well as lowering the cost of these processes. Syngas fermentation is always associated with acid production, which lowers the culture pH. Low pH provides an unfavorable environment for solvent production by clostridia. Redirecting the metabolic pathway toward solvent production by blocking acid production might enhance ethanol production.

More research is needed in this area. A study reported cell dormancy, hydrogen-uptake shutdowns, and a shift in pathways from acidogenesis to solventogenesis and vice versa, when the syngas was used without conditioning Datar et al. Ahmed and Lewis was able to overcome cell dormancy by introducing a 0.

Nitrous oxide NO was found to be a potential inhibitor of hydrog- enase enzyme activity, which reduced the available carbon for product formation Ahmed and Lewis However, since impurities generated can influence variables involved in the fermentation process, including pH, osmolarity, and redox potential and can directly inhibit enzymes and contribute to cell toxicity, a gas cleanup step is important to ensure a clean syngas is produced which does not contain components which will negatively interfere with the fermentation process Daniell et al.

Impurities in the synthesis and subsequent gas cleanup steps utilized will vary depending on the biomass feedstock Ahmed et al. Some gas cleaning techniques include tar cracking, wet cleaning, and the use of activated carbon and ZnO Boerrigter et al. Tar cracking techniques include catalytic cracking, thermal cracking, plasma cracking, scrubbing with water, and scrubbing with oil Rabou et al. Water- soluble substances are dissolved, including nitric oxide and ammonia.

Ahmed et al. Ultrasonic atomization, vapor recompression, vapor reuse and vacuum distillation, and selective adsorption of water are some of the alternative methods that have been examined in order to reduce the ethanol recovery cost Sato et al. Liquid—liquid extraction is a widely used separation technique for acetic acid recovery.


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A suitable solvent can be used in order to extract a substantially pure acetic acid solution. Fockedey et al. The goal in bioremediation is to stimulate microorganisms with nutrients and other chemicals that will enable them to destroy the contaminants Wu et al. This technology is considered as an effective and eco-friendly alternative to conventional remediation strategies Kazy et al. The bioremediation systems in operation today reply on microorganisms native to the contaminated sites, encouraging them to work by supplying them with the optimum levels of nutrients and other chemicals essential for their metabolism Margesin and Schinner ; Tyagi et al.

However, researchers are currently investigating ways to augment contaminated sites with non-native microbes—including genetically engineered microorganisms —specially suited to degrading the contaminants of concern at particular sites Crowford and Crowford ; Megharaj et al. It is possible that this pro- cess, known as bioaugmentation, could expand the range of possibilities for future bioremediation systems Tyagi et al. Regardless of whether the microbes are native or newly introduced to the site, an understanding of how they destroy contaminants is critical to understanding bioremediation.

The types of microbial processes that will be employed in the cleanup dictate what nutritional supplements the bioremediation system must supply Boopathy ; Crowford and Crowford ; Tiquia ; Megharaj et al. Furthermore, the by-products of microbial processes can provide indicators that the bioremediation is successful. Microorganisms gain energy by catalyzing energy-producing chemical reactions that involve breaking chemical reactions that involve breaking chemical bonds and transferring electrons away from the contaminant.

The contaminant is called the electron donor, while the electron recipient is called the electron acceptor. The energy gained from these electron transfers is then invested, along with some electrons and carbon from the contaminant, to produce more cells. These electron donor and acceptor are essential for cell growth and are called the primary substrates. Many microorganisms use O2 as the electron acceptor.

Why sequence carbon monoxide oxidizing thermophiles?

The process of destroying organic compounds with the aid of O2 is called aerobic respiration. In aerobic respiration, microbes use O2 to oxidize part of the carbon in the contaminants to carbon dioxide CO2 , with the rest of the carbon used to produce new cell mass. In the process, the O2 gets reduced, producing water. Thus, the major by-products of aerobic respiration are CO2, H2O, and an increased population of microorganisms.

Many microorganisms can exist without oxygen, using a process called anaerobic respiration. Researchers think that these carboxydotrophs may be involved in reducing potentially toxic carbon monoxide hotspots by combine with water to form hydrogen, carbon dioxide and acetate, which are in turn used for thermophilic energy conservation and carbon sequestration mechanisms. The project focuses on sequencing two closely related microbes, one of which is Carboxydothermus hydrogenformans.

A strain of C. Additionally, the hydrogen component of syngas can be used in fuel cells. The second microbe being sequenced is C. Department of Energy DOE. CRISPR-Cas9 is a powerful, high-throughput gene-editing tool that can help scientists engineer organisms for bioenergy applications. Cas9 needs guide RNA to lead it to the correct sequence to snip—but not all guides are effective. Skiadas , Hariklia N Gavala. References Publications referenced by this paper. A thermophilic microbial fuel cell design Sarah M.

Carver , Pertti Vuoriranta , Olli H.

Electricity generation from carbon monoxide in a single chamber microbial fuel cell. Carboxydothermus siderophilus sp. Tatiana V Slepova , Tatyana G. Sokolova , Tatyana V. Kolganova , Tatyana P. Tourova , Elizaveta A.