(161c) Investigation of Cyanobacterial Alkane Biosynthesis Pathway for Microbial Production of “Drop in” Biofuels

An alkane biosynthesis pathway originally from cyanobacteria has attracted great interest in the past several years for metabolic engineering for “drop in” biofuels, since its products (alkanes and alkenes) have high energy density and can be used directly as substitutes for gasoline, diesel and jet fuel without costly and energy-intensive chemical conversion. In this pathway, fatty acyl-CoA (ACP) is first converted by fatty acyl reductase (ACR) to aldehydes, which subsequently undergo decarbonylation catalyzed by aldehyde decarbonylase to yield alkanes and alkenes. To obtain knowledge of this newly-identified pathway, which will facilitate its engineering for biofuels and other biotechnology applications, over-expression, purification and initial characterization of ACR from Synechococus elongatus PCC7942 was performed.  ACR operates by a ‘ping-pong’ mechanism which involves an acyl-enzyme thioester intermediate, with k_cat = 0.36 ± 0.023 min^-1 , K_m (stearoyl-CoA) = 31.9 ± 4.2 µM and K_m (NADPH) = 35.6 ± 4.9 µM. We are currently evaluating the performance of this pathway in recombinant E. coli. Synthetic protein scaffolds and other methods are being employed to improve the efficiency of alkane and alkene synthesis.