title: Identification of enhanced hydrogen and ethanol Escherichia coli producer strains in a glycerol-based medium by screening in single-knock out mutant collections.
abstract: BACKGROUND
  Earth's climate is warming as a result of anthropogenic emissions of greenhouse gases from fossil fuel combustion. Bioenergy, which includes biodiesel, biohydrogen and bioethanol, has emerged as a sustainable alternative fuel source. For this reason, in recent years biodiesel production has become widespread but this industry currently generates a huge amount of glycerol as a by-product, which has become an environmental problem in its own right. A feasible possibility to solve this problem is the use of waste glycerol as a carbon source for microbial transformation into biofuels such as hydrogen and ethanol. For instance, Escherichia coli is a microorganism that can synthesize these compounds under anaerobic conditions.
  
  
  RESULTS
  In this work an experimental procedure was established for screening E. coli single mutants to identify strains with enhanced ethanol and/or H2 productions compared to the wild type strain. In an initial screening of 150 single mutants, 12 novel strains (gnd, tdcE, rpiA nanE, tdcB, deoB, sucB, cpsG, frmA, glgC, fumA and gadB) were found to provide enhanced yields for at least one of the target products. The mutations, that improve most significantly the parameters evaluated (gnd and tdcE genes), were combined with other mutations in three engineered E. coli mutant strains in order to further redirect carbon flux towards the desired products.
  
  
  CONCLUSIONS
  This methodology can be a useful tool to disclose the metabolic pathways that are more susceptible to manipulation in order to obtain higher molar yields of hydrogen and ethanol using glycerol as main carbon source in multiple E. coli mutants.
authors.affiliation: Department of Biomedicine, Biotechnology and Public Health-Biochemistry and Molecular Biology, Campus de Excelencia Internacional Agroalimentario (ceiA3), Institute of Biomolecules, University of Cádiz, Avda República Saharui s/n, 11510, Puerto Real, Cádiz, Spain. antonio.valle@uca.es.
authors.forename: Antonio
authors.initials: A
authors.lastname: Valle
authors.affiliation: Department of Chemical Engineering and Food Technology, Campus de Excelencia Internacional Agroalimentario (ceiA3), University of Cádiz, Avda República Saharui s/n, 11510, Puerto Real, Cádiz, Spain. gema.cabrera@uca.es.
authors.forename: Gema
authors.initials: G
authors.lastname: Cabrera
authors.affiliation: Department of Chemical Engineering and Food Technology, Campus de Excelencia Internacional Agroalimentario (ceiA3), University of Cádiz, Avda República Saharui s/n, 11510, Puerto Real, Cádiz, Spain. domingo.cantero@uca.es.
authors.forename: Domingo
authors.initials: D
authors.lastname: Cantero
authors.affiliation: Department of Biomedicine, Biotechnology and Public Health-Biochemistry and Molecular Biology, Campus de Excelencia Internacional Agroalimentario (ceiA3), Institute of Biomolecules, University of Cádiz, Avda República Saharui s/n, 11510, Puerto Real, Cádiz, Spain. jorge.bolivar@uca.es.
authors.forename: Jorge
authors.initials: J
authors.lastname: Bolivar
mesh_terms: D003470:Culture Media / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D055786:Gene Knockout Techniques; D005818:Genetic Engineering; D005990:Glycerol / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D009154:Mutation
chemical_list: D003470:Culture Media; D000431:Ethanol; D006859:Hydrogen; D005990:Glycerol