초록
<P><B>Summary</B></P><P>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 <I>V</I><I>ibrio</I> 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 <I>in vitro</I> enzymatic reactions using their recombinant proteins. Oxidation by an NADP<SUP>+</SUP>‐dependent AHG dehydrogenase and isomerization by an AHGA cycloisomerase are the two key AHG metabolic processes. This newly discovered metabolic route was verified <I>in vivo</I> by demonstrating the growth of <I>E</I><I>scherichia coli</I> 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 <I>E</I><I>. coli</I> strain increased the ethanol production in <I>E</I><I>. coli</I> 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.</P>