title: High cell density production of multimethyl-branched long-chain esters inEscherichia coliand determination of their physicochemical properties.
abstract: BACKGROUND
  Microbial synthesis of oleochemicals derived from native fatty acid (FA) metabolism has presented significant advances in recent years. Even so, native FA biosynthetic pathways often provide a narrow variety of usually linear hydrocarbons, thus yielding end products with limited structural diversity. To overcome this limitation, we took advantage of a polyketide synthase-based system fromMycobacterium tuberculosisand developed anEscherichia coliplatform with the capacity to synthesize multimethyl-branched long-chain esters (MBE) with novel chemical structures.
  
  
  RESULTS
  With the aim to initiate the characterization of these novel waxy compounds, here, we describe the chassis optimization of the MBE producerE. colistrain for an up-scaled oil production. By carrying out systematic metabolic engineering, we improved the final titer to 138.1 ± 5.3 mg MBE L-1in batch cultures. Fed-batch microbial fermentation process was also optimized achieving a maximum yield of 790.2 ± 6.9 mg MBE L-1with a volumetric productivity of 15.8 ± 1.1 mg MBE (L h)-1. Purified MBE oil was subjected to various physicochemical analyses, including differential scanning calorimetry (DSC) and pressurized-differential scanning calorimetry (P-DSC) studies.
  
  
  CONCLUSIONS
  The analysis of the pour point, DSC, and P-DSC data obtained showed that bacterial MBE possess improved cold flow properties than several plant oils and some chemically modified derivatives, while exhibiting high oxidation stability at elevated temperatures. These encouraging data indicate that the presence of multiple methyl branches in these novel esters, indeed, conferred favorable properties which are superior to those of linear esters.
authors.affiliation: Microbiology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Ocampo y Esmeralda (2000), Rosario, Argentina.
authors.forename: Simón
authors.initials: S
authors.lastname: Menendez-Bravo
authors.affiliation: Microbiology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Ocampo y Esmeralda (2000), Rosario, Argentina.
authors.forename: Julia
authors.initials: J
authors.lastname: Roulet
authors.affiliation: Microbiology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Ocampo y Esmeralda (2000), Rosario, Argentina.
authors.forename: Martín
authors.initials: M
authors.lastname: Sabatini
authors.affiliation: Microbiology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Ocampo y Esmeralda (2000), Rosario, Argentina.
authors.forename: Santiago
authors.initials: S
authors.lastname: Comba
authors.affiliation: US Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, 1815 N. University St, Peoria, IL 61604 USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Dunn
authors.affiliation: Microbiology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Ocampo y Esmeralda (2000), Rosario, Argentina.
authors.forename: Hugo
authors.initials: H
authors.lastname: Gramajo
authors.affiliation: Microbiology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Ocampo y Esmeralda (2000), Rosario, Argentina.
authors.forename: Ana
authors.initials: A
authors.lastname: Arabolaza
keywords: Escherichia coli; Fed-batch fermentation; Metabolic engineering; Oleochemicals; Wax production