title: The novel catabolic pathway of 3,6-anhydro-L-galactose, the main component of red macroalgae, in a marine bacterium.
abstract: The catabolic fate of the major monomeric sugar of red macroalgae, 3,6-anhydro-L-galactose (AHG), is completely unknown in any organisms. AHG is not catabolized by ordinary fermentative microorganisms, and it hampers the utilization of red macroalgae as renewable biomass for biofuel and chemical production. In this study, metabolite and transcriptomic analyses of Vibrio sp., a marine bacterium capable of catabolizing AHG as a sole carbon source, revealed two key metabolic intermediates of AHG, 3,6-anhydrogalactonate (AHGA) and 2-keto-3-deoxy-galactonate; the corresponding genes were verified in vitro enzymatic reactions using their recombinant proteins. Oxidation by an NADP(+) -dependent AHG dehydrogenase and isomerization by an AHGA cycloisomerase are the two key AHG metabolic processes. This newly discovered metabolic route was verified in vivo by demonstrating the growth of Escherichia coli harbouring the genes of these two enzymes on AHG as a sole carbon source. Also, the introduction of only these two enzymes into an ethanologenic E. coli strain increased the ethanol production in E. coli by fermenting both AHG and galactose in an agarose hydrolysate. These findings provide not only insights for the evolutionary adaptation of a central metabolic pathway to utilize uncommon substrates in microbes, but also a metabolic design principle for bioconversion of red macroalgal biomass into biofuels or industrial chemicals.
authors.affiliation: Department of Biotechnology, Korea University Graduate School, Seoul, 136-713, Korea.
authors.forename: Eun Ju
authors.initials: EJ
authors.lastname: Yun
authors.forename: Saeyoung
authors.initials: S
authors.lastname: Lee
authors.forename: Hee Taek
authors.initials: HT
authors.lastname: Kim
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Pelton
authors.forename: Sooah
authors.initials: S
authors.lastname: Kim
authors.forename: Hyeok-Jin
authors.initials: HJ
authors.lastname: Ko
authors.forename: In-Geol
authors.initials: IG
authors.lastname: Choi
authors.forename: Kyoung Heon
authors.initials: KH
authors.lastname: Kim
mesh_terms: D059001:Aquatic Organisms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D056804:Biofuels; D050260:Carbohydrate Metabolism; D004734:Energy Metabolism / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation / Q000235:genetics; D005690:Galactose / Q000031:analogs & derivatives* / Q000378:metabolism; D020869:Gene Expression Profiling; D053858:Metabolic Networks and Pathways / Q000235:genetics; D012624:Seaweed / Q000201:enzymology / Q000378:metabolism*; D014733:Vibrio / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
chemical_list: D056804:Biofuels; C117625:3,6-anhydrogalactose; D005690:Galactose