Impact of carbon monoxide partial pressures on methanogenesis and medium chain fatty acids production during ethanol fermentation. Issue 2 (30th October 2017)

• Record Type: Journal Article
• Authors: Esquivel‐Elizondo, Sofia; Miceli, Joseph; Torres, Cesar I.; Krajmalnik‐Brown, Rosa
• Is Part Of: Biotechnology and bioengineering. Volume 115:Issue 2(2018)
• Page Start: 341
• Page End: 350
• Publication Date: 2017-10-30
• Subjects: Acetobacterium -- CO fermentation -- CO partial pressure -- fatty acid chain elongation -- methanogenesis -- Peptostreptococcaceae; Biotechnology -- Periodicals; Bioengineering -- Periodicals; 660.6
• DOI: 10.1002/bit.26471
• Languages: English
• ISSNs: 0006-3592

Abstract

Abstract: Medium‐chain fatty acids (MCFA) are important biofuel precursors. Carbon monoxide (CO) is a sustainable electron and carbon donor for fatty acid elongation, since it is metabolized to MCFA precursors, it is toxic to most methanogens, and it is a waste product generated in the gasification of waste biomass. The main objective of this work was to determine if the inhibition of methanogenesis through the continuous addition of CO would lead to increased acetate or MCFA production during fermentation of ethanol. The effects of CO partial pressures ( P CO ; 0.08–0.3 atm) on methanogenesis, fatty acids production, and the associated microbial communities were studied in batch cultures fed with CO and ethanol. Methanogenesis was partially inhibited at P CO ≥ 0.11 atm. This inhibition led to increased acetate production during the first phase of fermentation (0–19 days). However, a second addition of ethanol (day 19) triggered MCFA production only at P CO ≥ 0.11 atm, which probably occurred through the elongation of acetate with CO‐derived ethanol and H2 :CO2 . Accordingly, during the second phase of fermentation (days 20–36), the distribution of electrons to acetate decreased at higher P CO, while electrons channeled to MCFA increased. Most probably, Acetobacterium, Clostridium, Pleomorphomonas, Oscillospira, and Blautia metabolized CO to H2 :CO2, ethanol and/or fatty acids, while Peptostreptococcaceae, Lachnospiraceae, and other Clostridiales utilized these metabolites, along with the provided ethanol, for MCFA production. These results are important for biotechnological systems where fatty acids production are preferred over methanogenesis, such as in chain elongation systems and microbial fuel cells. Abstract : Continuous addition of carbon monoxide (CO) (140–428 mmol/L) at CO partial pressures ≥0.11 atm to fermentation with small amounts of ethanol (22 mmol/L) inhibited methanogenesis and led to elongation of acetate (produced from ethanol) to propionate, butyrate and medium‐chain fatty acids (MCFA) with CO‐derived H2 :CO2 and ethanol. Clostridium, Peptostreptococcaceae, Lachnospiraceae, and other Clostridiales most likely partnered with carboxidotrophs, potentially Acetobacterium, Pleomorphomonas, Oscillospira, and Blautia species, for valerate, caproate, and heptanoate production.