Oxygen-tolerant coenzyme A-acylating aldehyde dehydrogenase facilitates efficient photosynthetic n-butanol biosynthesis in cyanobacteria

Ethan I. Lan, Soo Y. Ro, James C. Liao*

*Corresponding author for this work

Research output: Contribution to journalArticle

94 Scopus citations

Abstract

Metabolic engineering of photosynthetic microorganisms such as cyanobacteria for the production of fuels or chemicals is challenging, particularly when the pathway involves oxygen-sensitive enzymes. We have previously designed a coenzyme A (CoA) dependent n-butanol biosynthesis pathway tailored to the metabolic physiology of the cyanobacterium Synechococcus elongatus PCC 7942 by incorporating an ATP driving force and a kinetically irreversible trap. However, one of the enzymes involved, CoA-acylating butyraldehyde dehydrogenase (Bldh) is oxygen sensitive, therefore hindering efficient n-butanol synthesis in cyanobacteria. To overcome this obstacle of n-butanol biosynthesis, we characterized six oxygen tolerant CoA-acylating aldehyde dehydrogenases (PduP) from the 1,2-propandiol degradation pathway for their activity toward acyl-CoA. We showed that PduP catalyzes the reversible reduction of a broad range of acyl-CoAs (C2 to C12) into corresponding aldehydes. In particular, PduP from Salmonella enterica has the highest catalytic efficiency (kcat/Km) of 292 s-1 mM-1 for butyryl-CoA, which is about 7 times higher than that for acetyl-CoA. Finally, replacing Bldh with PduP in the n-butanol synthesis pathway resulted in n-butanol production to a cumulative titer of 404 mg L-1 with peak productivity of 51 mg per L per day, exceeding the base strain by 20 fold. Thus, the oxygen sensitivity of CoA-acylating aldehyde dehydrogenase appears to be a key limiting factor for cyanobacteria to produce alcohols through the CoA-dependent route.

Original languageEnglish
Pages (from-to)2672-2681
Number of pages10
JournalEnergy and Environmental Science
Volume6
Issue number9
DOIs
StatePublished - 1 Sep 2013

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