| Lignocellulosic biomass has long been recognized as a potential sustainable source of mixed sugars. Recent research has focused on the development of recombinant strain for efficient production of ethanol from lignocellulosic hydrolysates, together with high stress tolerance. In this study, we constructed the recombinant xylose-metabolizing strains of Zymomonas mobilis and demonstrated that expression of IrrE, a global regulator for extreme radiation resistance from Deinococcus radiodurans, confers significantly enhanced to tolerance to the environmental stresses in Z. mobilis. Futhermore, enthanol stress-responsive gene expression profiles of Escherichia coli strain and its rpoS mutant strain were analyzed using DNA microarrys.Four genes encoding xylose assimilation and pentose phosphate pathway enzymes (xylA/xylB, talB/tktA) from Escherichia coli and two promoters ( eno and gap) from Z. mobilis were constructed into the shuttle plasmid (pBBR1MCS-1) and transferred into Z. mobilis. The resulting recombinant strain PZ. mobilis fermented both glucose and xylose, which is essential for economical conversion of lignocellulosic biomass to ethanol. Enzymatic analyses of PZM strain grown in RM medium containing xylose of 40g/L showed the presence of XI ( 80U/mg proteins), XK(53U/mg proteins), TAL (1105U/mg proteins) and TKT (180U/mg proteins). The productivity of ethanol from glucose is 81.2% of theory value and 63.1% from xylose.The components (such as acetic acid) in lignocellulosic hydrolysates and the accumulation of ethanol during the fermentation can inhibit the growth and ethanol production of ethanologenic strains. To improve growth and ethanol production of Z. mobilis under the stresses, the D. radiodurans gene irrE were cloned and transferred into Z. mobilis to generate the recombinant strain. The results showed that the expression of IrrE regulator resulted in a significant increase in cell viability and the tolerance to ethanol, acetic acid, salt stresses.To further understand the effect of environmental stresses on the ethanol production in ethanologenic strains, DNA microarrys was used to analyze the expression profiles of E. coli and its rpoS mutant strain under the ethanol stress. The results showed that there are 799 differentially expressed genes by at least twofold in the logarithmic phase cells after 15% (v/v) ethanol shock for 15 min. The expression of 467 genes were up-regulated, while 305 genes were down-regulated. In stationary phase cells, among 1422 differentially expressed genes, 465 genes were up-regulated expression and 943 genes were down-regulated. Six major groups might contribute in various ways to the enhanced stress tolerance: (i) transcription, replication, translation, ribosomal structure and biogenesis, recombination and repair; (ii) energy production and conversion; (iii) lipid transport and metabolism; inorganic ion transport and metabolism, secondary metabolites biosynthesis, transport and catabolism, carbohydrate transport and metabolism, amino acid transport and metabolism, nucleotide transport and metabolism; (iv) signal transduction mechanisms, cell wall/membrane/envelope biogenesis, coenzyme transport and metabolism; (v)cell cycle control, cell division, chromosome partitioning; defense mechanisms, cell motility; (vi) posttranslational modification, protein turnover, chaperones.Analysis of these differentially expressed genes showed. Two osmotregulated trehalose synthesis genes otsAB and the betaine transport gene yehZ, were down-regulated, which may lead to trehalose and betaine decrease in mutant. In response to ethanol shock, the glutamate decarboxylase and related genes gadABC were down–regulated in mutant, which are important for stress-tolerance in E. coli. These results indicated RpoS play a global regulator role in ethanol tolerance in E. coli.
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