Bacteria could one day be making medicines for us from carbon dioxide
Scientists have taken a step towards freeing pharmaceuticals from dependence on fossil fuels
Scientists of diverse fields are exploring different ways to reduce the amounts of greenhouse gases in the atmosphere that threaten to plague societies for decades to come. The direst warnings for the planet are calling for us to go carbon-negative within the next few generations or face intolerable climatic conditions (the climatic disruptions we have seen so far are just the beginning). In addition to increasing carbon sequestration, we will also have to start using CO₂ to make goods and materials to replace everyday petrochemical products. In November, microbiologists from Israel, USA, Switzerland, and Germany announced that they developed a strain of bacteria that can absorb CO₂ from the atmosphere and incorporate it into biomass. That is to say, the organic material that makes up cells.
Plants can do this already, as can, in fact, many naturally-occurring bacteria, such as blue-green algae and hydrogen-consuming bacteria. What has never been done before is to take an organism that normally grows by converting carbs into cell matter, and make it use CO₂ instead. To capture CO₂ into a non-gaseous form is an energy-intensive process is called carbon fixation, which is how photosynthesis works. Other methods, however, can beat photosynthesis in terms of efficiency. Some of the new ways of fixing CO₂ could also produce items for human consumption. Most of the carbon we use in food, textiles, and fuel originates in agriculture and forestry, but this is far from ideal in many cases.
The laws of thermodynamics are pitched against us when we’re out to fix CO₂, because some of the energy that is released from burning fuels (whether it is wood, gasoline, or pop tarts), has to be put back into new chemical bonds. To give you an idea of what a great investment is required, think of the fact that RuBisCO, the key enzyme used for CO₂ fixation during photosynthesis, is probably the most abundant enzyme in existence, weighing in globally at around 700 million metric tons.
Pathway rewiring and targetted evolution for the breatharian lifestyle
Bacteria are extremely adaptable, and many have evolved to be super-efficient in the competition for resources. Nature has in fact, already produced bacteria that can fix CO₂ using light or chemicals that are typical waste products of anaerobic microorganisms, but the low energy available in these products means that these bacteria grow slowly, and are difficult to engineer genetically to produce desirable products. Instead, what the scientists have gone for is E. coli, the most studied species, and a fast-growing industrial beast to boot. By transferring to it four genes found in other bacteria, they added an additional metabolic circuit that allowed it to use the energy from a simple organic compound (formate) to fix CO₂. They also had to disable two native genes in order to ensure reactions didn’t flow the wrong way.
Initially, the organism could not use CO₂ to grow on despite having all the tools in place. It is actually pretty normal for an organism with new genes from another species, that the genes do not activate when expected. To coax the bacteria to start using the genes, they grew the new bacteria with very small amounts of a sugar it naturally uses, along with high levels of CO₂, to ease the switch. As the bacteria replicated, random spontaneous mutations cropped up that fixed the problem, and allow some cells to adapt to their new conditions. These evolved cells outgrew the others, which were still living on the meager sugar ration. The result was a bacterium that could grow with CO₂ as its only carbon source, an amazing feat for E. coli, whose natural habitat is the gut, where it thrives by fermenting carbohydrates.
A green economy is a diverse economy
Naturally, the E. coli strain is not able to fix CO₂ for free, but we can produce the formate that drives the reaction from CO₂ efficiently with electricity. You may have read about “Air Protein”, which is a really similar technology using hydrogen to power food production out of CO₂. In the future we will likely a number of different energy storage modes alongside rechargeable batteries, including hydrogen and formate, adapted to the needs of different applications.
By using bacteria that grow on food produced directly from renewable electricity such as solar or wind, we can free up more food-producing land for nature. It is an appealing prospect to combine the massive untapped renewable energy that our planet has to offer, with the molecular machinery that has been honed by billions of years of evolution (bacteria have been around much longer than other organisms). The solutions needed in order to shift to green technology are going to need to involve this kind of amalgamation of engineering and biology.
The reason is that the earth’s natural resources alone are not sufficient to replace the oil-based products we rely on for a modern standard of living. Most of our consumable carbon originates in carbs, fat, and protein are formed by just a few plants such as maize, soy, cereals, sugar beet, oilseeds, potatoes, and palm oil. These plants have been used for thousands of years, but their success has come at the price of biodiversity, as global demand has necessitated growing them in monocultures with a lot of industrial inputs. To reduce demand, some uses of these products could be diverted to non-plant sources being developed to be more efficient at converting the energy of the sun into biological products. This is because plants only convert a small amount of the sun’s energy into fixed carbon (less than 1% in sugarcane).
We are never going to lose our dependence on the soil for producing the fruits and vegetables we need for a balanced diet that includes all the vitamins and minerals we require, not least because the process and ritual of cooking food is a basic characteristic of the human race. However, many of the ways we use agricultural commodities have nothing to do with food, and we could be producing that carbon by more efficient processes. Biofuels and bioplastics are today made wastefully from oils and starch, which diverts resources from food production. Most medicines are also made from fossil carbon, but some are synthesized by bacteria growing on carbs from valuable hectares of farmland. The carbon is fixed typically in the form of starch or sugar and has to be purified and broken down and into glucose first before it can be used in this way.
Time for pharmaceutical companies to clean up their act
Again, E. coli is the most well-studied organism on the planet, but it is much more than a lab-rat, as it is also grown in order to produce a wide range of protein-based medicines. It has been used to drastically reduce the price of insulin for diabetic patients, and also produce treatments for various cancers, growth hormone deficiency, and hepatitis. While many therapeutic proteins are now produced in yeast and animal cell culture, about 30% are produced in bacteria, which have the edge when it comes to growth efficiency and yields.
Nobody really thinks about the environmental impact of pharmaceuticals though, apart from antibiotics in agriculture, and the hormones originating from sewage that affect fish some ten-twenty years ago now. They were more innocent days, when we still afforded some concern for the quality of life of cold-blooded creatures. Shifting baselines aside, it turns out that our addiction to fossil fuels extends even to our reliance on modern medicine, as scientists from McMaster University in Canada calculated, two years ago. They found that the pharmaceutical industry produces more greenhouse gases than the automotive industry, despite being considerably smaller in economic value.
Granted, those emissions stem from a broad range of sources, and the authors of the Canadian study state that it’s hard to identify the main culprits because the companies involved can be quite secretive and not particularly keen on drawing too much attention to the problem. But if we’re going to have continued access to basic drugs, such as those that the World Health Organization deems essential to any national health system, we need to start reducing our dependence on fossil fuels in this arena as well. The antibiotic-resistance crisis will become irrelevant if we can no longer even produce sufficient quantities of the antibiotics we have come to take for granted.
The new CO₂ -eating E. coli bug is still far from being plugged into the production line at Pfizer or Merck, but it is a step in the right direction to solving a neglected problem. For one thing, the bacterium still grows too slowly to be of practical use, so it still needs some adapting. Evolution has given rise to a range of different ways to fix CO₂, and it may turn out that another pathway is more effective for this novel mode of growth. It may seem odd to use formate for the energy to fix CO₂, resulting in the paradox that the strain actually produces more CO₂ than it consumes. The kicker is that formate is a low-energy carb, that can be easily produced with electricity. If the electricity is generated renewably, growth can be carbon-negative.
Formate and hydrogen can both efficiently be produced with electricity these days, so what is really going to help these technologies take off is when the economy makes the switch from fossil fuels to renewable electricity. We could even see coming to fruition a process that has been in development for about 10 years called “microbial electrosynthesis”. This uses species of bacteria that are able to take electricity, directly from an electrode, to power biochemical reactions. Needless to say, the electric current has to be kept low so it does not frazzle the cells, which limits this approach to really specific applications. What we need to see is more research into these approaches that really give us a fighting chance to sustain modern health care systems through the transition to a fossil fuel-free world
