Anthropogenic climate change and the rising world population, in combination with increasing urbanization, poses global challenges to our societies that can only be solved by technological advancement. The direct biotechnological use of greenhouse gases, including residual biomass flows from agriculture and urban centers, can help industrial production to become independent of fossil raw materials. The biological conversion of materials can thus pave the way for the transformation of industry toward a sustainable, circular economy into which material flows are integrated.
The negative impact of climate change on the global ecosystem is forcing industry and society to rethink and move towards a sustainable, circular economic system [1, 2]. At the heart of these activities are renewable, biobased raw material streams. Their mass and energy efficient conversion by means of combined, tailored biotechnological processes can help to sustainably produce food, materials, chemical base substances, and even pharmaceuticals in biorefineries  in a climate-neutral way. In contrast to first-generation biorefineries, current process chains increasingly use streams of biomass residues (e.g., straw, wood, algae) that do not compete with primary food production. Such processes must quantitatively demonstrate their economic and environmental viability through combined metrics of techno-economic and life cycle analyses . This paper will introduce three biotechnological process routes currently being researched for producing materials and chemical building blocks.
The Green Carbon process for producing CO2-based carbon fiber composites and functional lubricants
Fig. 1 Production of oil-rich algal biomass in cascade photobioreactors under realistic climate simulation at the TUM AlgaeTec Center
Anthropogenic climate change is largely due to excessive CO2 emissions emanating from the use of fossil fuels such as coal and petroleum. On the other hand microalgae, unicellular aquatic microorganisms, can perform photosynthesis to convert sunlight, the greenhouse gas CO2 and inorganic nutrient salts into biomass. They grow up to 10 times faster than terrestrial plants and can be cultivated on fallow land using saline or waste water, so there is no competition with agricultural activities. The photosynthetic efficiency of microalgae is about twice that of terrestrial plants. This makes them suitable biotechnological tools for efficient CO2 fixation and conversion into sustainable raw materials for the food, energy, chemical and cosmetics industries. Certain saltwater algae such as Microchloropsis salina are characterized by rapid growth and their very high CO2 conversion efficiency of up to 97 % (w/w) into biomass . Under metabolic stress such as nitrogen limitation, these algae additionally store oils up to 75 % (w/w) as an intracellular carbon reservoir [6, 7].
Fig. 2 Synergistic biotechnological and chemical conversion cascades from algae oil to carbon fiber composites, biofuels and specialty chemicals
The climate-centered optimization of algae cultivation performed in the globally unique AlgaeTec Center of the Technical University of Munich (TUM) accelerates the industrial application of such technologies, adapting specialized processes to match the climate conditions at ideal production locations such as Greece (Fig. 1). The extraction of algae oil by mechanical or enzymatic processes can pave the way for a wide variety of applications. While algae oil has hitherto been considered primarily for biofuels, a synergistic combination of biotechnological and chemical conversion routes is opening up new fields of application, such as producing carbon fiber composites and biodegradable lubricant components based on algae oil (Fig. 2). The resulting applications in the automotive and aircraft industries are even CO2-negative because they fixate the CO2 bound in the algae oil permanently in the carbon fiber. Since carbon fiber is chemically completely inert and does not degrade over geological time periods, the eventual disposal of carbon fiber materials at the end of their life cycle in, for example, mines would even serve as an efficient CO2 sink. This was confirmed by independent studies in the IPCC Special Report on Global Warming of 1.5 °C (SR1.5) . Applying this technology in the construction sector (e.g. for T-beams) would allow about two gigatons of CO2 per year to be fixated, precisely the amount currently emitted by the cement industry. This shows that innovative biotechnological processes can actively contribute to climate protection.
Sustainable crop protection using bioactive natural substances
Due to the observed increase in the average temperature and the resulting weather variations, climate change is leading to a drastic reduction in the amount of land available to agriculture. It has also been leading to the migration of pest insects previously unknown in Europe. To safeguard crops and thus our food supplies, plant protection measures must be ramped up. Conventional agriculture uses chemical substances to control insects but these are unsustainably produced from petrochemical precursors and can also kill useful insects such as bees [9, 10]. The non-selectivity of such substances and their overuse has led to legislative bans on many chemical insecticides in recent years .
Fig. 3 New concepts for sustainable plant protection (N. Mehlmer)
An alternative approach is to use bioactive natural products such as cembrandiol (CBT-ol), which was originally isolated from woodland tobacco (Nicotiana sylvestris). This natural product acts as a selective insect repellent, not killing the insects but repelling them . It does not show any effect on beneficial insects such as honey bees and thus does not negatively impact biodiversity. Because this natural product is biodegradable, is has no long-term effects on the ecosystem, unlike chemical insecticides. Extracting CBT-ol from tobacco is very costly, so such a process is not economically feasible. However, our research group has succeeded in producing CBT-ol in a genetically modified Escherichia coli strain. Unfortunately the production titers were very low due to the pronounced hydrophobicity of CBT-ol, which negatively affects cellular processes [13, 14]. However, in order to generate CBT-ol in industrially relevant amounts, the designed CBT-ol biosynthetic pathway is currently being transferred into an oil (triglyceride) producing bacterium. Like microalgae, these bacteria form intracellular oil vesicles under metabolic stress. Their intracellular “oil droplets” act as a metabolic sink for hydrophobic substances such as CBT-ol. As a result, significant amounts of CBT-ol accumulate in these oil droplets without exerting any toxic effects on the cell. After cell harvest and mechanical cell lysis, the CBT-ol containing oil droplets can easily be separated gravimetrically from the cell lysate. Interestingly, the metabolism of these oil-producing bacteria can utilize different sugars. This gives rise to the possibility of fermentatively producing CBT-ol from low-cost lignocellulosic residue materials such as straw. In the current research phase, the developed processes are being scaled up and their efficiency tested under realistic conditions. This new technology demonstrates that biotechnological processes can be used for sustainable crop protection to safeguard our future food supplies (Fig. 3).
Sustainable biotechnological production of bioactive natural substances to protect marine biodiversity
Marine ecosystems contain a large proportion of the world's biodiversity. Not only do they provide a significant share of humanity's food supply through fishery, fragile marine ecosystems such as coral reefs also act as a significant CO2 sink and thus as a bulwark against climate change. In addition, the biodiversity of coral reefs offers a hitherto unexploited source of new bioactive natural substances, some of which have completely new pharmaceutical modes of action. These ecosystems are increasingly coming under pressure from climate change and the unsustainable management of the world's oceans. To combat climate change and safeguard the biodiversity of global ecosystems, it is essential to protect marine ecosystems, especially coral reefs. This goes hand in hand with Goal 13 (climate action) and Goal 14 (life below water) of the UN’s Sustainable Development Goals. A prominent example of the unsustainable use of coral reef ecosystems is the extraction of pseudopterosins from the soft coral Antillogorgia elisabethae. These anti-inflammatory, highly effective natural compounds are currently used in skin creams and have already been tested in clinical trials [15, 16]. However, since demand far exceeds the natural resources and the extraction is based on coral harvesting and extraction, it is particularly important to find a sustainable means of production. Total chemical synthesis of natural products is a possible production route. However, due to the complex structures of terpene-based natural products, this involves the use of expensive organometallic catalysts and toxic solvents .
Fig. 4 An example (pseudopterosin) of the biotechnological production of new bioactive natural substances to protect marine biodiversity (M. Ringel)
A sustainable alternative to total chemical synthesis is biotechnological production using E. coli as a whole cell catalytic system (Fig. 4). The incorporation of the terpenoid biosynthetic pathway and a terpene synthase into E. coli, as well as the downstream in vitro functionalization of the terpene backbone, allow a key intermediate on the pathway to pseudopterosin synthesis to be sustainably produced for the first time . While using residue material streams as a nutrient source will be key to a sustainable, circular bioeconomy, producing key intermediates of pseudopterosin biosynthesis constitutes only one of many examples of sustainable biotechnological drug production. However, by incorporating biosynthetic pathways into whole cell catalytic systems such as E. coli, many other potentially bioactive natural products can be sustainably produced, while protecting coral reef biodiversity. This example vividly demonstrates the potential of protecting ecosystems and biodiversity, and at the same time creating value.
The technology platforms described above impressively demonstrate how synthetic biotechnological processes with different objectives can generate sustainable products that are not only climate neutral, but also counteract climate change, protecting our livelihoods and global biodiversity. Biotechnology will therefore be key to creating a sustainable circular economy.
The author of the article’s sections "The Green Carbon process for producing CO2-based carbon fiber composites and functional lubricants" is Professor Dr. Thomas Brück, while the section "Sustainable crop protection using bioactive natural substances" was authored by Dr. Norbert Mehlmer and Professor Dr. Thomas Brück. The author of the article’s section "Sustainable biotechnological production of bioactive natural substances to protect marine biodiversity" is Marion Ringel. Dr. Mahmoud Masri created the images in the section "The Green Carbon process for producing CO2-based carbon fiber composites and functional lubricants”.
Category: Bioeconomy | Synthetic Biotechnology
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Header image: iStock.com | RomoloTavani, IakovKalinin; detail TUM AlgaeTec Center © TUM; Antillogorgia elisabethae © Thomas Brück
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