Not only olive tree, rapeseed and Co – the blue-green algae cyanobacteria can produce oil, researchers have found. The tiny ones therefore have potential for sustainable feed or fuel production, the scientists say. Because the energy source of the cyanobacteria is light, they do not need any arable land and their oil production can possibly be increased in a targeted manner.
Energy-rich substances of a special kind – oils and fats from plants have a fundamental meaning for humans: They serve our nutrition, as feed and form the basis of numerous products – from skin cream to biodiesel. Vegetable oil production is based on the products of photosynthesis – the high-energy compounds are ultimately created by light, water and carbon dioxide. Nevertheless, it is well known that oil production by plants is not necessarily sustainable and climate-friendly: monocultures such as rapeseed fields or palm oil plantations consume enormous areas and are therefore problematic from an ecological perspective. Alternative options for bio-oil production are therefore in demand.
Target photosynthesis microbes
So far, it was assumed that the cyanobacteria were out of the question because only “real” plants were known to have the ability to produce oil. Because although they do photosynthesis and their nickname “blue-green algae” suggests otherwise, these organisms differ significantly in many characteristics from the plants. The cyanobacteria are even less related to rapeseed and Co than to our intestinal bacteria. Nevertheless, there is an interesting connection to the plants: It is assumed that the chloroplasts responsible for photosynthesis in plant cells are, as it were, cyanobacteria incorporated: According to the so-called endosymbiont hypothesis, over a billion years ago, a primal plant cell “swallowed” a cyanobacterium. The bacterium then lived on in the cell and supplied it with photosynthesis products.
This relationship now forms the basis of the current study. The research team led by Peter Dörmann from the University of Bonn has been working on an enzyme that is active in chloroplasts and plays a role in vegetable oil synthesis for some time. So the thought came up: “If the endosymbiont hypothesis is correct, the oil synthesis enzyme of the chloroplasts could also occur in cyanobacteria,” explains Dörmann. He and his colleagues first pursued this possibility through genetic tests. To do this, they searched the genes of Synechocystis cyanobacteria for genes that are similar to the genes for the well-known vegetable oil synthesis enzyme.
“Cyanobacteria oil” detected for the first time
And they found it: the researchers came across a gene for a so-called acyltransferase – this group also includes the oil synthesis enzymes known from plants. In further investigations, they were able to prove that this genetic makeup actually leads to the production of small amounts of previously unknown storage oils in the cyanobacteria examined. The researchers report that these are triacylglycerols and wax esters. As you emphasize, this result is very interesting from an evolutionary biological point of view: it provides evidence that a certain part of the oil synthesis machinery of plant chloroplasts actually goes back to the cyanobacteria.
But perhaps even more important is the practical potential that lies in the knowledge: cyanobacteria may be able to produce sustainable feed or biofuels, the scientists say. Because unlike oil plants like rapeseed, the frugal water dwellers do not need any arable land – a container with culture medium as well as light and heat are sufficient.
“There are already attempts to produce oils from vegetable green algae,” says Dörmann. “But these eukaryotes are difficult to keep and, moreover, they cannot be easily optimized biotechnologically for the highest possible oil production rate.” According to him, this could be different with the prokaryotic cyanobacteria. Dörmann admits that the species examined so far only produces very small amounts of oil. “But it is quite possible that other species are significantly more productive,” says the scientist. In addition, biotechnology offers opportunities: blue-green algae can be genetically modified relatively easily – similar to other bacteria. “So it is quite possible that the oil yield can be increased significantly by biotechnology,” says Dörmann.
Source: Rheinische Friedrich-Wilhelms-Universität Bonn, specialist article: PNAS, doi: 10.1073 / pnas.1915930117