Cross-reactions between engineered xylose and galactose pathways in recombinant Saccharomyces cerevisiae.
BACKGROUND
Overexpression of the PGM2 gene encoding phosphoglucomutase (Pgm2p) has been shown to improve galactose utilization both under aerobic and under anaerobic conditions. Similarly, xylose utilization has been improved by overexpression of genes encoding xylulokinase (XK), enzymes from the non-oxidative pentose phosphate pathway (non-ox PPP) and deletion of the endogenous aldose reductase GRE3 gene in engineered Saccharomyces cerevisiae strains carrying either fungal or bacterial xylose pathways. In the present study, we investigated how the combination of these traits affect xylose and galactose utilization in the presence or absence of glucose in S. cerevisiae strains engineered with the xylose reductase (XR)-xylitol dehydrogenase (XDH) pathway.


RESULTS
In the absence of PGM2 overexpression, the combined overexpression of XK, the non-ox PPP and deletion of the GRE3 gene significantly delayed aerobic growth on galactose, whereas no difference was observed between the control strain and the xylose-engineered strain when the PGM2 gene was overexpressed. Under anaerobic conditions, the overexpression of the PGM2 gene increased the ethanol yield and the xylose consumption rate in medium containing xylose as the only carbon source. The possibility of Pgm2p acting as a xylose isomerase (XI) could be excluded by measuring the XI activity in both strains. The additional copy of the PGM2 gene also resulted in a shorter fermentation time during the co-consumption of galactose and xylose. However, the effect was lost upon addition of glucose to the growth medium.


CONCLUSIONS
PGM2 overexpression was shown to benefit xylose and galactose fermentation, alone and in combination. In contrast, galactose fermentation was impaired in the engineered xylose-utilizing strain harbouring extra copies of the non-ox PPP genes and a deletion of the GRE3 gene, unless PGM2 was overexpressed. These cross-reactions are of particular relevance for the fermentation of mixed sugars from lignocellulosic feedstock.
Garcia Sanchez
Rosa
R
Department of Applied Microbiology, Lund University, P,O, Box 124, SE-22100 Lund, Sweden. marie-francoise.gorwa@tmb.lth.se.
Hahn-Hägerdal
Bärbel
B
Gorwa-Grauslund
Marie F
MF
Microb Cell Fact. 2010 May 27;9:40
20507616
Appl Environ Microbiol. 2000 Aug;66(8):3381-6
10919795
Appl Environ Microbiol. 1996 Dec;62(12):4648-51
8953736
Eur J Biochem. 1994 Feb 15;220(1):83-96
8119301
Yeast. 2008 Nov;25(11):835-47
19061191
Gene. 1990 Nov 30;96(1):23-8
2265755
J Bacteriol. 1995 Aug;177(15):4517-9
7635834
Appl Environ Microbiol. 2005 Nov;71(11):6465-72
16269670
FEMS Yeast Res. 2002 Aug;2(3):277-82
12702276
Appl Environ Microbiol. 2004 Apr;70(4):2307-17
15066826
Yeast. 2005 Apr 15;22(5):359-68
15806613
J Bacteriol. 1968 May;95(5):1727-31
5650080
Appl Microbiol Biotechnol. 1997 Aug;48(2):218-24
9299780
Gene. 1988 Dec 30;74(2):527-34
3073106
Methods Enzymol. 1982;89 Pt D:599-605
6216393
Biotechnol Bioeng. 2008 Oct 1;101(2):317-26
18421797
Yeast. 1995 Apr 15;11(4):355-60
7785336
J Biol Chem. 2007 Nov 2;282(44):31844-51
17804405
Biotechnol Bioeng. 2006 Mar 5;93(4):665-73
16372361
Appl Environ Microbiol. 1998 May;64(5):1852-9
9572962
FEMS Yeast Res. 2003 Oct;4(1):69-78
14554198
Microbiology (Reading). 2009 Apr;155(Pt 4):1340-1350
19332835
Appl Microbiol Biotechnol. 2007 Apr;74(5):937-53
17294186
Curr Genet. 1990 Dec;18(6):493-500
2127555
Appl Environ Microbiol. 1997 May;63(5):1959-64
9143128
Yeast. 1993 Jul;9(7):761-70
8368010
Appl Environ Microbiol. 1996 Sep;62(9):3187-95
8795209
Microbiol Rev. 1987 Dec;51(4):458-76
2830478
Microbiology (Reading). 2002 Sep;148(Pt 9):2783-2788
12213924
Gene. 1979 May;6(1):23-8
383576
Microb Cell Fact. 2007 Feb 05;6:5
17280608
Appl Environ Microbiol. 2001 Dec;67(12):5668-74
11722921
Enzyme Microb Technol. 2000 Jun 1;26(9-10):688-698
10862874
Mol Microbiol. 1997 Aug;25(3):483-93
9302011
Microb Cell Fact. 2005 Nov 10;4:31
16283927