Specific Ethanol Production Rate in Ethanologenic <i>Escherichia coli</i> Strain KO11 Is Limited by Pyruvate Decarboxylase

Abstract

Modification of ethanol productivity and yield, using mineral medium supplemented with glucose or xylose as carbon sources, was studied in ethanologenic Escherichia coli KO11 by increasing the activity of five key carbon metabolism enzymes. KO11 efficiently converted glucose or xylose to ethanol with a yield close to 100% of the theoretical maximum when growing in rich medium. However, when KO11 ferments glucose or xylose in mineral medium, the ethanol yields decreased to only 70 and 60%, respectively. An increase in GALP_Ec (permease of galactose-glucose-xylose) or PGK_Ec (phosphoglycerate kinase) activities did not change xylose or glucose and ethanol flux. However, when PDC_Zm (pyruvate decarboxylase from Zymomonas mobilis) activity was increased 7-fold, the yields of ethanol from glucose or xylose were increased to 85 and 75%, respectively, and organic acid formation rates were reduced. Furthermore, as a response to a reduction in acetate and ATP yield, and a limited PDC_Zm activity, an increase in PFK_Ec (phosphofructokinase) or PYK_Bs (pyruvate kinase from Bacillus stearothermophilus) activity drastically reduced glucose or xylose consumption and ethanol formation flux. This experimental metabolic control analysis showed that ethanol flux in KO11 is negatively controlled by phosphofructokinase and pyruvate kinase, and positively influenced by the PDC_Zm activity level.

Biohydrogen production using psychrophilic bacteria isolated from Antarctica

“…A02, N04, GA051 and GAOF, cumulated between 6.28 and 6.76 g/l ethanol, which corresponded to a yield of 0.31e0.35 g ethanol/g glucose. These values are comparable to those reported for the alcohologenic microorganisms used for bioethanol production [33]. This finding is also relevant since it is possible to develop processes using these strains for simultaneous production of hydrogen and ethanol, which today is the more i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 4 ) 1 e7…”

Metabolic engineering and adaptive evolution ofEscherichia coliKO11 for ethanol production through the Entner-Doudoroff and the pentose phosphate pathways

“…Under non‐aerated conditions the ethanologenic E. coli strain KO11 produces ethanol efficiently by using glucose as carbon source through the glycolytic pathway with a yield of 2 mol of ethanol per mol of glucose . It also produces acetate (with concomitant production of ATP), formate and lactate . In this study, we found that strain KO11 Δ pgi is not able to grow under non‐aerated conditions in minimal medium with glucose (Fig.…”

“…Specific rates of glucose consumption (q S ), ethanol production (q Et‐OH ), and organic acid formation (acetate, formate and lactate) were estimated during the exponential phase. These rates were converted to product flux as reported elsewhere …”

Can Microbially Derived Advanced Biofuels Ever Compete with Conventional Bioethanol? A Critical Review

“…Therefore, it is apparent that extensive research is required to convert both C6 and C5 sugars to advanced biofuels in reasonable titer and yield. (Nakamura and Whited 2003;Atsumi et al 2008;Huerta-Beristain et al 2008;Whited et al 2010;Wang et al 2011;Huffer et al 2012 Despite the high robustness and industrial relevance of S. cerevisiae, the strain naturally does not ferment pentose sugars (Palmqvist and Hahn-Hagerdal 2000). In addition to integrating xylose and arabinose utilization pathways (e.g., expression of XYL1, XYL2, and XYL3 genes), there have been several efforts focusing on the over expression of specific pentose transporters and the genes of the non-oxidative part of pentose phosphate pathways (Kuyper et al 2005;Hahn-Hagerdal et al 2007).…”