The Prokaryotic Microalga Limnothrix redekei KNUA012 to Improve Aldehyde Decarbonylase Expression for Use as a Biological Resource

The prokaryotic microalga Limnothrix redekei KNUA012 isolated from a freshwater bloom sample from Lake Hapcheon, Hapcheon-gun, South Korea, was investigated for its potential as a biofuel feedstock. Microalgae produce straight-chain alkanes/alkenes from acyl carrier protein-linked fatty acyls via aldehyde decarbonylase (AD; EC 1.2.1.3), which can convert aldehyde intermediates into various biofuel precursors, such as alkanes and free fatty acids. In L. redekei KNUA012, long-chain ADs can convert fatty aldehyde intermediates into alkanes. After heterologous AD expression in Escherichia coli (pET28-AD), we identified an AD in L. redekei KNUA012 that can synthesize various alkanes, such as pentadecane (C 15 H 32 ), 8-heptadecene (C 17 H 34 ), and heptadecane (C 17 H 36 ). These alkanes can be directly used as fuels without transesterification. Biodiesel constituents including dodecanoic acid (C 13 H 26 O 2 ), tetradecanoic acid (C 15 H 30 O 2 ), 9-hexa decenoic acid (C 17 H 32 O 2 ), palmitoleic acid (C 17 H 32 O 2 ), hexadecanoic acid (C 17 H 34 O 2 ), 9-octadecenoic acid (C 19 H 36 O 2 ), and octadecanoic acid (C 19 H 38 O 2 ) are produced by L. redekei KNUA012 as the major fatty acids. Our findings suggest that Korean domestic L. redekei KNUA012 is a promising resource for microalgae-based biofuels and biofuel feedstock.