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Published on: August 9, 2024
Mixed-Carbon Fermentation with Hydrocarbons and Fatty Acids for Enhanced Medium-Chain-Length Polyhydroxyalkanoate
Krishanthi Bandara1, Masoumeh Mohandessi1, Xianglan Bai2
1Department of Chemical and Biomedical Engineering, University of Missouri, 416 S 6th Street, Columbia, MO 65211, USA.
Abstract:
Mixed-carbon streams containing fatty acids and hydrocarbons are relevant to polyhydroxyalkanoate (PHA) biomanufacturing, particularly for valorizing waste and upcycling plastics that yield chemically diverse substrates. This study evaluated fatty acids (C6-C18), hydrocarbons (C6-C18), and their mixtures for medium-chain-length polyhydroxyalkanoate (mcl-PHA) production by Pseudomonas putida (PP), Pseudomonas resinovorans (PR), and a PP-PR co-culture. Among individual fatty acids, decanoic acid (C10) resulted in the highest cell concentration (2.05g/L). Medium-chain-rich fatty-acid mixtures (C6-C12, with or without C14) promoted PHA accumulation, whereas C8-containing hydrocarbon feeds favored growth. The PP-PR co-culture grown on the mixed hydrocarbon-fatty-acid formulation HCFA-1 achieved the highest PHA content among the tested configurations (60.96wt%), with a titer of 2.11g/L. The polymers consisted predominantly of (R)-3-hydroxyoctanoic acid (HO) and (R)-3-hydroxydecanoic acid (HD), with (R)-3-hydroxydodecanoic acid (HDD) as a secondary component and variable amounts of (R)-3-hydroxyhexanoic acid (HHx) and (R)-3-hydroxytetradecanoic acid (HTD). C8-rich substrate mixtures favored HO, whereas C10-rich mixtures increased the HD fraction. Thus, feed composition can tailor polymer composition in addition to supporting microbial growth and PHA accumulation. Because HO and HD differ in side-chain length, these compositional shifts may affect chain packing and crystallization. Adjusting the HO:HD ratio could therefore help tailor flexibility and thermal behavior for packaging films, coatings, and other value-added bioplastics. Although PHA titers were modest, this study examined substrate-composition effects rather than high-titer process optimization. These findings link mixed-carbon utilization to tunable mcl-PHA composition and provide guidance for designing feed formulations for targeted bioplastic applications.
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