title: Complex physiology and compound stress responses during fermentation of alkali-pretreated corn stover hydrolysate by an Escherichia coli ethanologen.
abstract: The physiology of ethanologenic Escherichia coli grown anaerobically in alkali-pretreated plant hydrolysates is complex and not well studied. To gain insight into how E. coli responds to such hydrolysates, we studied an E. coli K-12 ethanologen fermenting a hydrolysate prepared from corn stover pretreated by ammonia fiber expansion. Despite the high sugar content (∼6% glucose, 3% xylose) and relatively low toxicity of this hydrolysate, E. coli ceased growth long before glucose was depleted. Nevertheless, the cells remained metabolically active and continued conversion of glucose to ethanol until all glucose was consumed. Gene expression profiling revealed complex and changing patterns of metabolic physiology and cellular stress responses during an exponential growth phase, a transition phase, and the glycolytically active stationary phase. During the exponential and transition phases, high cell maintenance and stress response costs were mitigated, in part, by free amino acids available in the hydrolysate. However, after the majority of amino acids were depleted, the cells entered stationary phase, and ATP derived from glucose fermentation was consumed entirely by the demands of cell maintenance in the hydrolysate. Comparative gene expression profiling and metabolic modeling of the ethanologen suggested that the high energetic cost of mitigating osmotic, lignotoxin, and ethanol stress collectively limits growth, sugar utilization rates, and ethanol yields in alkali-pretreated lignocellulosic hydrolysates.
authors.affiliation: Great Lakes Bioenergy Research Center, Madison, Wisconsin, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Schwalbach
authors.forename: David H
authors.initials: DH
authors.lastname: Keating
authors.forename: Mary
authors.initials: M
authors.lastname: Tremaine
authors.forename: Wesley D
authors.initials: WD
authors.lastname: Marner
authors.forename: Yaoping
authors.initials: Y
authors.lastname: Zhang
authors.forename: William
authors.initials: W
authors.lastname: Bothfeld
authors.forename: Alan
authors.initials: A
authors.lastname: Higbee
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Grass
authors.forename: Cameron
authors.initials: C
authors.lastname: Cotten
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Reed
authors.forename: Leonardo
authors.initials: L
authors.lastname: da Costa Sousa
authors.forename: Mingjie
authors.initials: M
authors.lastname: Jin
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Balan
authors.forename: James
authors.initials: J
authors.lastname: Ellinger
authors.forename: Bruce
authors.initials: B
authors.lastname: Dale
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Kiley
authors.forename: Robert
authors.initials: R
authors.lastname: Landick
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000693:Anaerobiosis; D048168:Escherichia coli K12 / Q000254:growth & development / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism* / Q000633:toxicity*; D005285:Fermentation; D020869:Gene Expression Profiling; D005947:Glucose / Q000378:metabolism; D013312:Stress, Physiological; D003313:Zea mays / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D000431:Ethanol; D005947:Glucose