Effect of overexpression of Saccharomyces cerevisiae Pad1p on the resistance to phenylacrylic acids and lignocellulose hydrolysates under aerobic andoxygen-limited conditions
S. Larsson et al., Effect of overexpression of Saccharomyces cerevisiae Pad1p on the resistance to phenylacrylic acids and lignocellulose hydrolysates under aerobic andoxygen-limited conditions, APPL MICR B, 57(1-2), 2001, pp. 167-174
Lignocellulose hydrolysates, obtained by acid hydrolysis for production of
bioethanol, contain, in addition to fermentable sugars, compounds that inhi
bit the fermenting micro-organism. One approach to alleviate the inhibition
problem is to use genetic engineering to introduce increased tolerance. Ph
enylacrylic acid decarboxylase (Pad1p) catalyses a decarboxylation step, by
which aromatic carboxylic acids are converted to the corresponding vinyl d
erivatives. Pad1p-overexpressing Saccharomyces cerevisiae was cultivated in
synthetic medium in the presence of model compounds, ferulic acid [(2 E)-3
-(4-hydroxy-3-methoxyphenyl)prop-2-enoic acid] and cinnamic acid [(2 E)-3-p
henylprop-2-enoic acid], as well as in a dilute acid hydrolysate of spruce
to examine the resistance against fermentation inhibitors. Overexpression o
f S. cerevisiae phenylacrylic acid decarboxylase (Pad1p) resulted in an imp
roved growth rate and ethanol productivity in the presence of ferulic acid,
cinnamic acid, and in a dilute acid hydrolysate of spruce. Vinyl guaiacol
(2-methoxy-4-vinylphenol) was identified as a major metabolite of ferulic a
cid, and dihydroferulic acid [3-(4-hydroxy-3-methoxyphenyl)propanoic acid]
was detected under oxygen-limited conditions. Styrene (vinylbenzene) and di
hydrocinnamic acid (3-phenylpropanoic acid) were identified as metabolites
of cinnamic acid. Transformants overexpressing Pad1p had the ability to con
vert ferulic and cinnamic acid at a faster rate than a control transformant
(PAD(C)) not overexpressing Pad1p. This enabled faster growth for Pad1p-ov
erexpressing transformants under both aerobic and oxygen-limited conditions
. Pad1p activity was also studied using nongrowing cells. The overexpressin
g transformants showed approximately tenfold higher activity than PADc. The
Pad1p overexpressing transformants also showed a 22-25% faster glucose con
sumption rate, a 40-45% faster mannose consumption rate, and a 24-29% faste
r ethanol production rate in the dilute acid hydrolysate of spruce.