Biology Reference
In-Depth Information
11
CHAPTER
Synthetic Biology of
Microbial Biofuel
Production: From Enzymes
to Pathways to Organisms
Gregory Bokinsky
1
, Dan Groff
1
and Jay Keasling
1,2,3
1
Joint BioEnergy Institute, Emeryville, CA, USA
2
University of California, CA, USA
3
Lawrence Berkeley National Laboratory, Berkeley, CA, USA
207
INTRODUCTION
The microbial generation of hydrocarbons, either from inexpensive plant biomass or directly
from sunlight, could provide a renewable and carbon-neutral source of liquid transportation
fuels, so long as the biomass is grown and harvested sustainably.
1,2
The explosive advances
in synthetic biology and metabolic engineering have dramatically accelerated efforts to
engineer microbes for fuel production (
Table 11.1
). Thanks to an ever-decreasing cost of
DNA synthesis and new, robust tools for DNA manipulation, our abilities to install
whatever DNA sequence we can imagine into a widening range of host microbes are more
powerful than ever, even up to the scale of installing whole genomes into cells.
3
The sheer
number of enzymes available in gene databases, and the incredible breadth of chemical
transformations they catalyze, represents vast biosynthetic versatility that can be harnessed
in simple cloning steps. These capabilities are already being applied to engineer microbial
production of valuable chemicals, such as pharmaceuticals, fragrances, and vitamins.
However, the current low cost of petrochemicals is a tremendous barrier to an economy-
wide adoption of microbially produced bulk compounds such as fuels and plastics.
Biologically generated commodity compounds will only be competitive with petrochemicals
when inexpensive bioprocesses are finally developed. These processes will feature robust
microbes capable of high product titers at near-theoretical yields. Achieving this ambitious
goal will likely require every trick known to synthetic biology.
Synthetic biologists have already taken many of the steps towards this goal. Microbial
production of biofuels with combustion properties similar to existing fuels has been
repeatedly demonstrated at proof-of-concept levels.
4
7
However, we still cannot
underestimate the challenge of genetically rewiring the physiology and metabolism of
microbes to reliably generate chemicals at a commodity scale. Our understanding of how
synthetic DNA sequences will behave once they are inside a cell still severely lags behind
