U Copenhagen team discovers “reverse photosynthesis” process for the breakdown of biomass for fuels or chemicals production
Researchers at the University of Copenhagen have discovered a natural process for the breakdown of biomass they describe as “reverse photosynthesis”—as opposed to the building of biomass as is the case with photosynthesis. Combined with a specific enzyme, the energy of sunlight can break down plant biomass.
Oxidative processes are essential for the breakdown of plant biomass. Lytic polysaccharide monooxygenases (LPMOs)—a class of powerful and widely distributed oxidative enzymes—oxidize the most recalcitrant polysaccharides. These enzymes require extracellular electron donors. In their work, described in an open access paper in the journal Nature Communications, the University of Copenhagen team researchers investigated the effect of using excited photosynthetic pigments as electron donors.
This is a game changer, one that could transform the industrial production of fuels and chemicals, thus serving to reduce pollution significantly. It has always been right beneath our noses, and yet no one has ever taken note: photosynthesis by way of the sun doesn’t just allow things to grow, the same principles can be applied to break plant matter down, allowing the release of chemical substances. In other words, direct sunlight drives chemical processes. The immense energy in solar light can be used so that processes can take place without additional energy inputs.—University of Copenhagen Professor Claus Felby, who led the research
LPMOs are found in fungi, bacteria and viruses, spanning a number of terrestrial and aquatic ecosystems. The enzymes play an essential role, yet not well-understood, in the turnover of organic matter, the Copenhagen researchers noted.
All identified substrates are naturally abundant polysaccharides including cellulose, hemicellulose, starch and chitin; the products are oxidized oligosaccharides and their non-oxidized counterparts.
LPMOs require an extracellular electron donor to complete their catalytic cycle. Proteins and plant-derived molecules have been found to serve as donors, but the specific types of electron donors, as well as the mechanism of electron transfer are still unresolved.
The apparent promiscuity of LPMOs with respect to the source of electrons, prompted us to investigate the effect of one of the most potent electron donors in nature namely chlorophylls, which are essential components of the photosynthetic light-harvesting and reaction centre complexes.—Cannella et al.
The researchers do not yet know how widespread “reverse photosynthesis” using light, chlorophyll and monooxygenases, is in nature, but there are many indications that fungi and bacteria use reverse photosynthesis as a “Thor’s hammer” to access sugars and nutrients in plants.
The discovery means that by using the sun, we can produce biofuels and biochemicals for things like plastics—faster, at lower temperatures and with enhanced energy-efficiency. Some of the reactions, which currently take 24 hours, can be achieved in just 10 minutes by using the sun.—Postdoc David Cannella, lead author
The breakthrough is the result of collaborative, multidisciplinary research at the Copenhagen Plant Science Centre that spans the disciplines of plant science, biotechnology and chemistry.
Reverse photosynthesis has the potential to break down chemical bonds between carbon and hydrogen, a quality that may be developed to convert biogas-plant sourced methane into methanol, a liquid fuel, under ambient conditions. As a raw material, methanol is very attractive, because it can be used by the petrochemicals industry and processed into fuels, materials and chemicals.
Additional research and development is required before the discovery can directly benefit society, but its potential is, “one of the greatest we have seen in years,” according to Professor Felby.
D. Cannella, K. B. Möllers, N.-U. Frigaard, P. E. Jensen, M. J. Bjerrum, K. S. Johansen & C. Felby (2016) “Light-driven oxidation of polysaccharides by photosynthetic pigments and a metalloenzyme” Nature Communications 7, Article number: 11134 doi: 10.1038/ncomms11134