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The novel catabolic pathway of 3,6‐anhydro‐ L ‐galactose, the main component of red macroalgae, in a marine bacterium
Author(s) -
Yun Eun Ju,
Lee Saeyoung,
Kim Hee Taek,
Pelton Jeffrey G.,
Kim Sooah,
Ko HyeokJin,
Choi InGeol,
Kim Kyoung Heon
Publication year - 2015
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.12607
Subject(s) - biology , biochemistry , metabolic pathway , catabolism , bioconversion , fermentation , galactose , escherichia coli , bacteria , industrial microbiology , marine bacteriophage , metabolic engineering , metabolite , enzyme , gene , genetics
Summary 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 V ibrio 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 E scherichia 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.