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Yeast bred to bear artificial vanilla
Scientists co-opt fungi to produce flavor more efficiently
Two species of yeast have
been engineered to make
vanillin (right), the dominant
flavor compound in vanilla.
By Rachel Ehrenberg
A jug of wine, a loaf of bread and now,
Yeast has long been pressed into service for making food and drink, and now
scientists have recruited the fungus for a
loftier flavor: vanillin, vanilla’s dominant
compound. Scientists report in the May
Applied and Environmental Microbiology
that they have engineered two strains of
yeast to produce vanillin from glucose,
a greener and cheaper route than previous methods.
“This is absolutely beautiful work,”
says John Rosazza, a medicinal and natural products chemist at the University
of Iowa in Iowa City. There is a huge market for vanillin, Rosazza says.
Vanillin is the dominant compound of
the hundreds that are found in vanilla — an
extract from the seed-bearing pods, called
beans, of orchids in the genus Vanilla.
But real vanilla beans are precious, rare
and costly. Today, less than 1 percent
of the vanillin sold each year is derived
from the orchids. The majority is synthe-
cose, a cheap and available sugar. To make
the yeast convert the glucose to vanillin,
the team added genes that encode for specific enzymes that spur the biochemical
reactions. These genes
included versions of
one from a dung mold, two bacterial genes and a human gene.
The team also knocked out a
gene that directs the conversion of vanillin to an undesirable form. The researchers say
they were pleased with the yields:
Fission yeast made 65 milligrams
per liter of liquid in the flasks,
baker’s yeast 45 mg/l.
To further increase the yeast
yield of vanillin, the researchers
added an additional gene that encodes
for an enzyme that converts the straight
vanillin into a form with a sugar attached,
vanillin beta-D -glucoside. This form isn’t
toxic, says Møller, allowing the yeast to
hold more of the compound. Both the
straight and sugar-laden vanillin could
be used in foods and perfumes.
While synthetic vanillin doesn’t offer
the rich flavors of true vanilla, the artificial
form has its place, says Daphna Havkin-Frenkel, director of research and development at Bakto Flavors in Rutgers, N. J.
sized in chemistry labs, and
typically made from lignin, a
constituent of wood left over
from the paper-making industry, or guaiacol, which is derived from
Scientists previously have used microorganisms to make vanillin, but the precursors are expensive and the process
involves environmentally unfriendly
chemicals, says Jørgen Hansen of Evolva
Biotech’s Copenhagen office. Also, vanillin itself is toxic to many microbes.
Now Hansen, Birger Lindberg Møller
of the University of Copenhagen and
colleagues have created a chemistry lab
within two different species of yeast growing in flasks: Schizosaccharomyces pombe,
also known as fission yeast, and
Saccharo-myces cerevisiae, baker’s or brewer’s yeast.
Instead of using the typical, expensive
starting material, the team turned to glu-
A good look at mimi
bottom: xiao ET AL.,/PLOS BIOLOG Y 2009
Scientists have zoomed in on mimivirus, the enormous
virus with the delicate name that has perplexed researchers since its discovery in 1992. its size (its diameter is
more than 10 times that of the virus that causes the
common cold) and its hodgepodge of genetic and structural traits blur the line of what is alive, says michael
Rossmann of Purdue university in West lafayette, ind.
Rossmann and an international team report the results
of their reconnaissance online april 28 in PLoS Biology.
Cryo-electron microscopy images reveal the details of a
starfish-shaped structure (a, b) that covers an opening in
the virus coat through which Dna might be expelled when
the virus infects a host. the Dna is enveloped in a membrane, seen in gray in reconstructed renderings (C, D).
the new work may help scientists understand if and how
the virus could cause disease. — Rachel Ehrenberg