Anyone wishing to make money with biotechnological fermentation processes is advised to select the substrate wisely. This is because the bacteria\u2019s \u201cfood\u201d usually consumes around two thirds of total production costs. Professor Peter D\u00fcrre is all too well aware of this particular problem. The experienced biotechnologist from Ulm has long applied his own techniques by feeding his ethanol-producing bacteria on synthesis gases containing carbon instead of the usual starch- or sugar-based substrates. Leading chemical companies in Germany are following D\u00fcrre\u2019s developments with keen interest. BASF, LANXESS, Bayer, Evonik and others are still in the \u201cpassenger seat\u201d, as D\u00fcrre puts it, but this state of affairs is likely to change as soon as the new approaches are seen to be successful.
\nProf. Peter D\u00fcrre coordinates the Clostridium project.\u00a0(\u00a9 University of Ulm)
\nIn Europe at least, the food versus fuel debate has accelerated the use of substrates like cellulose in place of sugar- and starch-based substrates that compete with food production. However, the oil glut and the associated fall in the price of oil have created economic difficulties for many biofuel producers. Patience, it seems, is a virtue on the long and winding road to second generation fuels, patience that British Petroleum ran out of in 2014, when it decided to discontinue all activities related to the production of ethanol from cellulose (Biofuel Digest, 18th January 2015).<\/p>\n
Meanwhile, American LanzaTech \u2013 a long-term cooperation partner of Prof. Peter D\u00fcrre, director of the Institute of Microbiology and Biotechnology at the University of Ulm \u2013 is now working on using synthesis gas for fermentation and has set up large-scale facilities in China with the initial aim of using microorganisms for producing ethanol from gas mixtures. D\u00fcrre is however convinced that more expensive products will follow as soon as the company has enough production organisms available.<\/p>\n
Cheap and available in huge quantities<\/p>\n
As the time is apparently not yet ripe for producing ethanol from cellulose, fermenters tend to resort to gases as alternative carbon sources. Carbon-containing gas mixtures are available in huge quantities in China and many other countries. These gas mixtures are a lot cheaper than crude oil and it is estimated that they will also be available in 50 years’ time.<\/p>\n
Carbon is present as carbon dioxide (CO2) in the emissions of power plants or the steel and cement industries. Carbon dioxide reduction requires hydrogen. Carbon is also available in synthesis gas (or syngas) in the form of carbon monoxide (CO), which has been used by the chemical industry for quite some time. Syngas is a gas mixture consisting mainly of hydrogen and carbon monoxide. Industrial exhaust gases such as carbon monoxide and carbon dioxide are currently either used for combustion or are released into the atmosphere (by steel producers or oil refineries).<\/p>\n
Carbon recycling is economically appealing, but unfortunately can only make a small contribution to reducing the greenhouse effect, as D\u00fcrre explains. In addition to LanzaTech, INEOS Bio and Caskat (also from the USA) also use syngas.<\/p>\n
\u201cSyngas fermentation is a relatively simple process,\u201d says D\u00fcrre. Syngas is fed into the fermentation reactor where the bacteria use it to grow and convert it into fuel and chemicals. Anaerobic, autotrophic bacteria of the genus Clostridium are particularly suitable for this purpose as are potentially aerobic, CO-oxidising bacteria of the genus Oligotropha. D\u00fcrre has been studying Clostridium bacteria for around 30 years. In the absence of oxygen, homoacetogenic, autotrophic bacteria such as those of the genus Clostridium convert the carbon monoxide contained in the syngas into acetate, ethanol and 2,3-butanediol by way of the Wood-Ljungdahl (or reductive acetyl-CoA pathway) where hydrogen is used as an electron donor.<\/p>\n
In order for the bacteria to be able to use syngas effectively, biotechnologists need to develop specific process techniques and reactors as well as modify the bacteria by way of metabolic engineering so that they can produce large quantities of bulk chemicals for the chemical industry and for biofuels. D\u00fcrre is coordinating a BMBF-funded project (“Gases as novel carbon source for biotechnological fermentations”) which is being carried out in cooperation with Prof. Dr.-Ing. Ralf Takors (University of Stuttgart, Institute of Bioprocess Engineering) and Prof. Dr.-Ing. Dirk Weuster-Botz (Munich University of Technology, Department of Bioprocess Engineering). The project got underway on March 1st 2015 and is receiving 3.3 million euros in funding from the BMBF over a period of three years.<\/p>\n
The following bacteria have to prove their suitability as chemical production platforms: Clostridium aceticum, C. carboxidivorans, C. ljungdahlii and C. ragsdalei. The project is specifically focused on the production of long-chain carbon compounds of major industrial importance as starting materials for syntheses, solvents and biofuels, including isobutanol (C4 product), isoprenoids (C5-based product), hexanol (C6 product) and bifunctional molecules such as 1,4-butanediol and 1,6-hexanediol. D\u00fcrre explains that the latter are of prime importance for the chemical industry. The project\u2019s scientific advisory board includes representatives from the chemical industry.<\/p>\n
D\u00fcrre and his colleagues need to solve a fundamental problem of anaerobic bacteria like Clostridia, which only require small amounts of energy for growth. However, genetically modified bacteria with energy-consuming synthesis pathways produce little or no ethanol. The researchers are therefore using Oligotropha carboxidovorans, a group of bacteria that convert carbon monoxide in the presence of oxygen. Transferring this process into industrial application is a delicate matter because the combination of CO and O2 results in a rather explosive mixture. Oligotropha uses oxygen for respiration, so has a respiratory chain and is able to produce energy-rich compounds such as ATP quite effectively. These microorganisms therefore have a lot more energy than anaerobic bacteria.<\/p>\n
The aerobic metabolisation of syngas has the potential to open up access to complex and energy-intensive product syntheses. In the time the project has to run, the researchers expect to have developed syngas-based laboratory-scale processes for the production of 1,4-butanediol, isobutanol, 1,6-hexanediol and hexanol.<\/p>\n
In addition to the BMBF-funded project, D\u00fcrre is also coordinating an EU-funded project (ERA-IB-2, CO2CHEM) on microbial gas fermentation. The project also commenced on March 1st. The consortium, which consists of academics from Frankfurt, Nottingham and Copenhagen and manufacturers from LanzaTech and Siemens, is aiming to develop a commercial fermentation process based on CO2 and H2 within the next three years. The cooperation partners are using Acetobacterium woodii, an anaerobic microbe that produces the platform chemical 3-hydroxypropionic acid (3-HP), to develop a more economical alternative to biotechnological fermentation that requires sugar as substrate.<\/p>\n
D\u00fcrre is excited about this collaboration with LanzaTech and Siemens. The latter uses a device that was originally developed for the production of hydrogen in the chemical industry, and which now has the potential of being used for something completely new.<\/p>\n
Researchers from Baden-W\u00fcrttemberg universities and companies (D\u00fcrre\/University of Ulm; Takors and Hauer\/University of Stuttgart and Syldatk\/KIT) are working on demonstrating that chemical products such as propene, 1,4-butadiene, ethylene glycol, 1,4-butanediol and 1,6-hexanediol can be produced economically from syngas by Clostridium ljungdahlii. The research cluster \u201cSustainable and Efficient Biosyntheses\u201d was established in autumn 2013 and is funded by the Baden-W\u00fcrttemberg Ministry of Science, Research and the Arts. It involves ten research groups that are working on three subprojects.<\/p>\n
D\u00fcrre is convinced that the desired substrate shift is possible and that large-scale microbial syngas fermentation will be implemented within the next five to ten years, which, in his view, will put an end to the food versus fuel debate.<\/p>\n","protected":false},"excerpt":{"rendered":"
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