Engineered Microbial Consortium for the Efficient Conversion of Biomass to Biofuels Page: 17
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1.9 Transcriptomic Profiling of Zymomonas mobilis Under Ethanol Stress [69]
Ethanol acts as an inhibitor of the cell growth and metabolism in Z. mobilis, thus resulting
in the decrease of the rate of sugar conversion to ethanol [69]. Michel et al. [70] found that
differential expression of related proteins are involved in ethanol-shock response, and the first
genome sequence of Z. mobilis ZM4 by Jeffries [71] suggested that sigma factor (E ZMO4104)
may play an important role in resisting ethanol stress. In a recent study by He et al. [69], microarray
technology was used to investigate the expression profiling of the ethanologenic Z. mobilis in
response to ethanol stress. 1800 gene fragments were amplified by PCR and spotted onto a glass
slide and using the microarray, the global transcriptional response of Z. mobilis ZM4 to ethanol
stress was examined at 24 h post-inoculation under normal (media with no ethanol) and stress
conditions (media with 5% ethanol). Of the 1800 genes examined by microarray analysis, 127
genes (7% of the total number of open reading frames represented on the array) were identified as
being significantly up- or down-regulated (fold change > 2.0, P<0.05) during ethanol stress
condition. Eighty-nine genes were up-regulated after 24 h post-inoculation under ethanol stress
condition and 38 genes were down-regulated. Approximately 34% of the genes down-regulated in
the presence of ethanol were related to metabolism. In the presence of ethanol, about 62% of the
genes related to regulation, cell processes, transport and unknown function showed greater
expression as compared to normal conditions. Nearly 24% of the genes, including plasmid
encoding genes, showed greater expression under stress condition. Twenty-three Entner-
Doudoroff pathway mRNAs such as glk, zwf pgl, pgk and eno, as well as ethanol fermentation-
related genes like pdc and adhB were shown to be less abundant under stress conditions but at
levels not considered significant. The ORFs related to stress shock-responsive molecular
chaperone complex proteins, such as DnaK, DnaJ, GrpE, HSP-33, etc. were also not affected17
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Anieto, Ugochukwu Obiakornobi. Engineered Microbial Consortium for the Efficient Conversion of Biomass to Biofuels, dissertation, August 2014; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc699973/m1/28/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .