Fig. 5

Biosynthesis pathway of expanding carbon chain for producing advanced biofuels using reverse β-oxidation intermediates. This biosynthesis pathway can use acetyl-CoA as a carbon chain elongation factor. Normal carbon chain extension in microorganisms occurs when (Cn + 2)-acyl-CoA molecules are broken down into acetyl-CoA and (Cn)-acetyl CoA molecules under the control of four genes (atoB, fadA, fadB, and fadE). However, chain elongation occurring through the addition of acetyl-CoA to another thioester due to β-oxidation cycle metabolic pathway is essentially reversible. Thus, advanced biofuels could be produced after one turn of this cycle. YqeF acetyl-CoA acetyltransferase; fadA ketoacyl-CoA thiolase; fadB hydroxyacyl-CoA dehydrogenase and enoyl-CoA hydratase; YdiO enoyl-CoA reductase; TES thioesterase; AcoAR acylCoA reductase; ADH alcohol dehydrogenase; aceEF-lpdA pyruvate dehydrogenase multi-enzyme complex; acetyl-CoA acetoacetyl-CoA transferase; atoB acetyl-CoA acyltransferase; atoE putative short-chain fatty acid transporter; dhaKLM PEP-dependent dihydroxyacetone kinase; fadA 3-ketoacyl-CoA thiolase; fadB enoyl-CoA hydratase/3-hydroxyaceyl-CoA dehydrogenase; fadD fatty acyl-CoA synthetase; fadE acyl-CoA dehydrogenase; fadL long-chain fatty acid outer membrane transporter; fbaA and fbaB: fructose-1,6-bisphosphate aldolase; fdhF formate dehydrogenase; galP galactose permease; gldA glycerol dehydrogenase; glk glucokinase; glpF glycerol MIP channel; hycB-1 hydrogenase; pflB pyruvate formate lyase; ptsHI-crr: ptsG glucose specific phosphoenolpyruvate phosphotransferase system; pykA and pykF pyruvate kinase; tpiA triose phosphate isomerase; xylA xyloseisomerase; xylB xylulokinase; xylE xylose MFS transporter; xylFGH: xylose ABC transporter. 2[H]: NAD(P)H = FADH2; DHA dihydroxyacetone, DHAP dihydroxyacetone-phosphate; Fructose-1: 6-BP fructose-1,6-bisphosphate. The red arrow shows the oxidation–reduction pathway to higher biofuel. The blue arrow is the carbon chain extension pathway