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 (C₁₅H₃₂), 8-heptadecene (C₁₇H₃₄), and heptadecane (C₁₇H₃₆). These alkanes can be directly used as fuels without transesterification. Biodiesel constituents including dodecanoic acid (C₁₃H₂₆O₂), tetradecanoic acid (C₁₅H₃₀O₂), 9-hexa decenoic acid (C₁₇H₃₂O₂), palmitoleic acid (C₁₇H₃₂O₂), hexadecanoic acid (C₁₇H₃₄O₂), 9-octadecenoic acid (C₁₉H₃₆O₂), and octadecanoic acid (C₁₉H₃₈O₂) 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.