title: Cultivation strategies for production of (R)-3-hydroxybutyric acid from simultaneous consumption of glucose, xylose and arabinose by Escherichia coli.
abstract: BACKGROUND
  Lignocellulosic waste is a desirable biomass for use in second generation biorefineries. Up to 40% of its sugar content consist of pentoses, which organisms either take up sequentially after glucose depletion, or not at all. A previously described Escherichia coli strain, PPA652ara, capable of simultaneous consumption of glucose, xylose and arabinose was in the present work utilized for production of (R)-3-hydroxybutyric acid (3HB) from a mixture of glucose, xylose and arabinose.
  
  
  RESULTS
  The Halomonas boliviensis genes for 3HB production were for the first time cloned into E. coli PPA652ara, leading to product secretion directly into the medium. Process design was based on comparisons of batch, fed-batch and continuous cultivation, where both excess and limitation of the carbon mixture was studied. Carbon limitation resulted in low specific productivity of 3HB (<2 mg g(-1) h(-1)) compared to carbon excess (25 mg g(-1) h(-1)), but the yield of 3HB/cell dry weight (Y3HB/CDW) was very low (0.06 g g(-1)) during excess. Nitrogen-exhausted conditions could be used to sustain a high specific productivity (31 mg g(-1) h(-1)) and to increase the yield of 3HB/cell dry weight to 1.38 g g(-1). Nitrogen-limited fed-batch process design led to further increased specific productivity (38 mg g(-1) h(-1)) but also to additional cell growth (Y3HB/CDW=0.16 g g(-1)). Strain PPA652ara did under all processing conditions simultaneously consume glucose, xylose and arabinose, which was not the case for a reference wild type E. coli, which also gave a higher carbon flux to acetic acid.
  
  
  CONCLUSIONS
  It was demonstrated that by using E. coli PPA652ara, it was possible to design a production process for 3HB from a mixture of glucose, xylose and arabinose where all sugars were consumed. An industrial 3HB production process is proposed to be divided into a growth and a production phase, and nitrogen depletion/limitation is a potential strategy to maximize the yield of 3HB/CDW in the latter. The specific productivity of 3HB reported here from glucose, xylose and arabinose by E. coli is further comparable to the current state of the art for production from glucose sources.
authors.affiliation: School of Biotechnology, Division of Industrial Biotechnology, KTH Royal Institute of Technology, SE 106 91, Stockholm, Sweden. johanjar@kth.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Jarmander
authors.affiliation: School of Biotechnology, Division of Industrial Biotechnology, KTH Royal Institute of Technology, SE 106 91, Stockholm, Sweden. jarosl@kth.se.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Belotserkovsky
authors.affiliation: School of Biotechnology, Division of Industrial Biotechnology, KTH Royal Institute of Technology, SE 106 91, Stockholm, Sweden. gustavsj@kth.se.
authors.forename: Gustav
authors.initials: G
authors.lastname: Sjöberg
authors.affiliation: School of Biotechnology, Division of Industrial Biotechnology, KTH Royal Institute of Technology, SE 106 91, Stockholm, Sweden. mguevara@kth.se.|Center of Biotechnology, Faculty of Science and Technology, Universidad Mayor de San Simón, Cochabamba, Bolivia. mguevara@kth.se.
authors.forename: Mónica
authors.initials: M
authors.lastname: Guevara-Martínez
authors.affiliation: School of Biotechnology, Division of Industrial Biotechnology, KTH Royal Institute of Technology, SE 106 91, Stockholm, Sweden. mnpz@kth.se.|Center of Biotechnology, Faculty of Science and Technology, Universidad Mayor de San Simón, Cochabamba, Bolivia. mnpz@kth.se.
authors.forename: Mariel
authors.initials: M
authors.lastname: Pérez-Zabaleta
authors.affiliation: Center of Biotechnology, Faculty of Science and Technology, Universidad Mayor de San Simón, Cochabamba, Bolivia. jorgeqs@supernet.com.bo.
authors.forename: Jorge
authors.initials: J
authors.lastname: Quillaguamán
authors.affiliation: School of Biotechnology, Division of Industrial Biotechnology, KTH Royal Institute of Technology, SE 106 91, Stockholm, Sweden. gen@kth.se.
authors.forename: Gen
authors.initials: G
authors.lastname: Larsson
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000096:biosynthesis*; D000101:Acetyl-CoA C-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D001089:Arabinose / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018533:Biomass; D019149:Bioreactors / Q000382:microbiology; D002849:Chromatography, Gas; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D020632:Halomonas / Q000201:enzymology / Q000235:genetics; D060847:Metabolic Engineering / Q000379:methods; D015203:Reproducibility of Results; D014994:Xylose / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D014994:Xylose; D001089:Arabinose; D000429:Alcohol Oxidoreductases; C023744:acetoacetyl-CoA reductase; D000101:Acetyl-CoA C-Acetyltransferase; D005947:Glucose; D020155:3-Hydroxybutyric Acid