Abstract
Cyanobacteria photosynthetically produce long-chain hydrocarbons, which are considered as infrastructure-compatible biofuels. However, native cyanobacteria do not produce these hydrocarbons at sufficient rates or yields to warrant commercial deployment. This research sought to identify specific genes required for photosynthetic production of alkanes to enable future metabolic engineering for commercially viable production of alkanes. The two putative genes (alr5283 and alr5284) required for long-chain hydrocarbon production in Anabaena sp. PCC 7120 were knocked out through a double crossover approach. The knockout mutant abolished the production of heptadecane (C17H36). The mutant is able to be complemented by a plasmid bearing the two genes along with their native promoters only. The complemented mutant restored photosynthetic production of heptadecane. This combined genetic and metabolite (alkanes) profiling approach may be broadly applicable to characterization of knockout mutants, using N2-fixing cyanobacteria as a cellular factory driven by solar energy to produce a wide range of commodity chemicals and drop-in-fuels from atmospheric gases (CO2 and N2 gas) and mineralized water.
Highlights
Oil reserves worldwide are limited, and as prices have risen, renewable fuels have become increasingly important
Identification of heptadecane emitted from Anabaena 7120 A Gas chromatography/mass spectrometry (GC/MS) analysis of volatile compounds emitted from wildtype Anabaena 7120 revealed a prominent peak at retention time 6.31 min (Fig. 1a)
Bioinformatics analysis to identify hydrocarbon biosynthesis genes Hydrocarbon biosynthesis genes have been identified in the cyanobacterial species S. elongatus PCC 7942 (Schirmer et al 2010)
Summary
Oil reserves worldwide are limited, and as prices have risen, renewable fuels have become increasingly important. Is there a biofactory that can convert carbon dioxide, water, and sunlight into fuels? Several species of cyanobacteria are known to produce and secrete low levels of alkanes and alkenes using carbon dioxide, water, and sunlight (Schirmer et al 2010). Cyanobacteria provide numerous advantages as living “biofuel factories”. As photosynthetic organisms, they remove CO2 from the atmosphere to form usable carbon products (sugars, isoprenoids, fatty acids, amino acids, etc.) that support cell growth and maintenance. Fatty acids have been shown to participate in an active recycling process within the cell membrane (Kaczmarzyk and Fulda 2010).
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