(23c) Engineering Yarrowia Lipolytica for Production of Medium Chain Fatty Acids and Alcohols

Authors: 
Rutter, C., Univeristy of Illinois - Urbana Champaign
Rao, C. V., University of Illinois, Urbana Champaign
Zhang, S., University of Illinois at Urbana Champaign

Engineering Yarrowia
lipolytica
for the Production of Medium Chain Fatty Acids and Alcohols

Lipids are naturally derived
molecules containing long alkyl chains that represent an attractive renewable
alternative to petroleum derived products. Fatty acids can be further converted
to other derivatives including (1) methyl and ethyl esters which can be used as
biodiesel, (2) fatty waxes to be used in cosmetics, food, and paper industries,
(3) fatty alcohols with applications as surfactants and industrial solvents, and
(4) alkanes that can directly be used as fuel[1-4]. Medium chain fatty acids and their
corresponding derivatives, however, more closely match the desired chemical and
physical properties of widely used petroleum-based chemicals. We employed the
oleaginous yeast Yarrowia lipolytica, which is capable of producing
lipids to titers ~20-fold higher than traditional yeasts from sugar substrates,
to produce medium chain fatty acids and alcohols[5, 6].
Five different Acyl-ACP thioesterases with specificity for medium chain
fatty-acyl ACPs were expressed in Y. lipolytica resulting in production
of either decanoic or octanoic acid at up to 40% of the total cell lipids.

Figure 1: Abundance of Total Lipids of specific chain length in strains of Y. lipolytica PO1f expressing five different Acyl-ACP-thioesterases

The reduction in fatty acid chain
length resulted in a two-fold increase in specific lipid productivity. The
yeast's native machinery was able to further modify these medium chain fatty
acids and incorporate them equally into all relevant classes of lipid molecules
including acyl-glycerides, esters, sterols, and free fatty acids. Furthermore,
reduction in fatty acid length resulted in an overall change in the relative
abundance of each lipid class.

Figure 2: Specific lipid yields of Y. lipolytica PO1f strains expressing different Acyl-ACP Thioesterases

Figure3: Abundance of each lipid class in Y. lipolytica PO1f strains expressing different Acyl-ACP Thioesterases

More than twice as much of the
naturally produced sixteen and eighteen carbon fatty acids remained in the form
of free fatty acids compared to the wild-type strain. Concurrent expression of
a fatty acyl-CoA reductase in medium chain fatty acid producing strains
resulted in the formation of the corresponding fatty alcohol.

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