Genetic Tweaking of Microbes Boosts Oil Production

Microbes ooze oil for renewable energy from Biodesign Institute on Vimeo.

Cyanobacteria species Synechocystis is getting a genetic makeover. The bacteria has learned to release its oil without dying -- which may boost oil production significantly.

The researchers had earlier modified these microbes to self-destruct and release their lipid contents. In the group’s latest effort however, the energy-rich fatty acids were extracted without killing the cells in the process. Lead author Xinyao Liu hypothesized that if cyanobacteria could overproduce fatty acids, the accumulation within the cells would eventually cause these fatty acids to leak out through the cell membrane. To accomplish this, Liu introduced genes for the expression of the enzyme thioesterase into the cyanobacteria.

Thioesterase clips the bonds associating the fatty acids with more complex molecules. This use of modified thioesterases to cause secretion of fatty acids was first described for Escherichia coli by John Cronan of the University of Illinois more than a decade ago.

A second series of modifications enhances the secretion process, by genetically deleting or modifying two key layers of the cellular envelop—the S and peptidoglycan layers—allowing fatty acids to more easily escape outside the cell, where their low water solubility causes them to precipitate out of solution, forming a whitish residue on the surface. Study results showed a 3-fold increase in fatty acid yield, after genetic modification of the two membrane layers.

To improve the fatty acid production even further, the group added genes to cause overproduction of fatty acid precursors and removed some cellular pathways that were non-essential to the survival of cyanobacteria. Such modifications ensure that the microbe’s resources are devoted to basic survival and lipid production.

Liu et al. made five successive generations of genetic modifications into the photosynthetic microbe. The mutant strains were able to overproduce fatty acids and secrete them into the medium at an efficiency of up to 133 ± 12 mg/L of culture per day at a cell density of 1.5 × 108 cells/mL (0.23 g of dry weight/liter). _GCC

In other bioenergy news, Michigan State University researchers have concluded that corn stover is the most profitable cellulosic biomass crop in the US. This would be true for the same reasons that sugar cane bagasse would be the most profitable cellulosic biomass crop in Brazil and the tropics. Because it is already there.

Tobacco is increasingly being seen as a potentially profitable crop for bio-oils, bio-sugars, and bio-mass.

A look at biomass feedstocks, and the effect of genetic modification.

It is impossible to adequately cover all the work that is being done worldwide in the development of bioenergy. But it is highly likely that within 10 years, bioenergy will begin to make a strong impression on energy markets. It is quite possible that the positive benefits of biomass bioenergy will help the local and regional economies before they begin to rock the global energy economy.