Microbial production of 1-octanol: A naturally excreted biofuel with diesel-like properties

Abstract

The development of sustainable, bio-based technologies to convert solar energy and carbon dioxide into fuels is a grand challenge. A core part of this challenge is to produce a fuel that is compatible with the existing transportation infrastructure. This task is further compounded by the commercial desire to separate the fuel from the biotechnological host. Based on its fuel characteristics, 1-octanol was identified as an attractive metabolic target with diesel-like properties. We therefore engineered a synthetic pathway specifically for the biosynthesis of 1-octanol in Escherichia coli BL21(DE3) by over-expression of three enzymes (thioesterase, carboxylic acid reductase and aldehyde reductase) and one maturation factor (phosphopantetheinyl transferase). Induction of this pathway in a shake flask resulted in 4.4 mg 1-octanol L−1 h−1 which exceeded the productivity of previously engineered strains. Furthermore, the majority (73%) of the fatty alcohol was localised within the media without the addition of detergent or solvent overlay. The deletion of acrA reduced the production and excretion of 1-octanol by 3-fold relative to the wild-type, suggesting that the AcrAB–TolC complex may be responsible for the majority of product efflux. This study presents 1-octanol as a potential fuel target that can be synthesised and naturally accumulated within the media using engineered microbes.

Tolerance engineering in bacteria for the production of advanced biofuels and chemicals

“…The AcrAB-TolC system, and specifically the AcrB protein, have been used in directed-evolution studies to further improve its activity for solvents such as 1-hexene [75], a-pinene, and 1-octanol [76] and several mutations that may affect substrate specificity or protein assembly have been identified (Figure 2). AcrAB-TolC was also found to be required for wild type tolerance and maximal production of aromatic compounds such as styrene [75] and the long-chain alcohol 1-octanol [77] in E. coli. In the case of 1-octanol, deletion of acrA led to a threefold reduction in total levels of the final product attributed specifically to reduced levels in the media fraction, indicating that AcrAB-TolC exports this compound and is required for optimal production [77].…”

An overview of the effects of fuel molecular structure on the combustion and emissions characteristics of compression ignition engines

“…Although much focus has been placed on the identification of non-edible feedstocks for the production of biodiesel, 17 a wide range of chemical and biological processes are currently under study with potential for the production of fuel molecules suitable for compression ignition combustion. Alkanes, alkenes, alcohols, methane and hydrogen can be produced from genetically modified micro-organisms including photosynthetic micro-algae, [18][19][20][21] whereas catalytic upgrading of fermentation products can result in higher-weight alcohols and ketones. 22,23 Many methods of combined thermal, chemical and biological treatment of lignocellulosic biomass can produce ketones, short-chain fatty acid esters, acids, furans, methane and phenols.…”

Reactive force field simulation studies on the combustion behavior of n -octanol

“…Starting with furfural and acetone, an overall 73% yield of n-octanol was obtained in a step-wise procedure and 54% overall in a one-pot procedure. Akhtar et al [17] have engineered a synthetic pathway for the synthesis of n-octanol from glucose and fatty acids in Escherichia coli BL21 (DE3) by overexpression of three enzymes (thioesterase, carboxylic acid reductase and aldehyde reductase) and one maturation factor (phosphopantetheinyl transferase).The majority (73%) of the fatty alcohol was localised within the media without a requirement of detergent or solvent overlay.…”

“…The viscosity of n-octanol (4.4 cST @ 40°C) is again close to the upper limit of the diesel viscosity range (1.8-5.8 cST @ 40°C ), while the boiling point of n-octanol (195°C) is at the low end of the diesel boiling curve (180-300°C). Overall, based on properties, noctanol is a suitable fuel for operation in compression ignition (CI) engines [17].…”