In the attempt to find alternative sources of energy, scientists are probing possibilities in almost the entire world of life. This includes plant life, of course, with trees, corn (maize), switch grass, and other crops in the list. It also includes smaller forms of plant life, in particular algae. Even smaller forms of life and the photosynthetic precursor to plants are cyanobacteria. The attempts to produce hydrocarbons from bacteria are all over the map, literally and figuratively. Even though bacteria reproduce very rapidly, their ability to produce hydrocarbons is difficult to scale – to make in quantity – because feedstocks (what they live on) and processing (extraction) can be costly.
Researcher Xinyao Liu and Professor Roy Curtiss at Arizona State University’s Biodesign Institute (USA) believe they have a viable approach. They have genetically modified the common cyanobacteria to not only produce lipids (oil) that can easily be a replacement for petroleum, but the bacteria excrete the oil as a byproduct of their normal life cycle. In short, this is oil production from a living organism that does not need extraction, and does not kill the organism.
The key to the approach was the realization that a previous technique that modified cyanobacteria to produce energy rich fatty acids could be accelerated so that the cyanobacteria would naturally expel the excess production through the cell membrane (a process of diffusion). To achieve the acceleration a specific enzyme, thioesterase, was introduced into the cyanobacteria. This enzyme frees fatty acids from more complex proteins and allows them to accumulate until the cell secretes them. (This was a technique first described for E. Coli bacteria by John Cronan of the University of Illinois more than ten years ago.)
A further genetic modification was then used to produce cyanobacteria with a cell membrane that allows fatty acids to more easily escape the cell. This modification increased the fatty acid yield by a factor of three (3x). Additional genes were added to ensure overproduction of fatty acid precursors (molecules needed to produce the acids) and they removed some protein production pathways that used cell resources but were not needed for cyanobacteria survival. These changes helped the cyanobacteria use its resources for basic survival and lipid production.
Professor Roy Curtiss, noted that “the seminal advance has been to combine a number of genetic modifications and enzyme activities previously described in other bacteria and in plants in the engineered cyanobacteria strains along with the introduction of newly discovered modifications to increase production and secretion of fatty acids. The results to date are encouraging and we are confident of making further improvements to achieve enhanced productivity in strains currently under construction and development. In addition, optimizing growth conditions associated with scale-up will also improve productivity.”
Like many approaches to using bacteria for hydrocarbon production, this one must now go through the ramp-up from laboratory quantities to something akin to commercial level production. In this process, it will be learned if the approach is economically viable – costs of production allowing – and if the oil produced is competitive with other energy sources, including of course, petroleum.