Branched Medium Chain Fatty Acids: Iso-Caproate Formation from Iso-Butyrate Broadens the Product Spectrum for Microbial Chain Elongation

Abstract

Chain elongation fermentation can be used to convert organic residues into biobased chemicals. This research aimed to develop a bioprocess for branched medium chain fatty acids (MCFAs) production. A long-term continuous reactor experiment showed that iso-caproate (4-methyl pentanoate, i-C6) can be produced via ethanol based chain elongation. The enriched microbiome formed iso-caproate from iso-butyrate at a rate of 44 ± 6 mmol C L–1 day–1 during the last phase. This amounted to 20% of all formed compounds based on carbon atoms. The main fermentation product was n-caproate (55% of all carbon), as a result of acetate and subsequent n-butyrate elongation. The microbiome preferred straight-chain elongation over branched-chain elongation. Lowering the acetate concentration in the influent led to an increase of excessive ethanol oxidation (EEO) into electron equivalents (e.g., H2) and acetate. The formed acetate in turn stimulated straight chain elongation, but the resulting lower net acetate supply rate towards straight chain elongation led to an increased selectivity towards and productivity of i-C6. The electrons produced via oxidation routes and chain elongation were apparently utilized by hydrogenotrophic methanogens, homoacetogens, and carboxylate-to-alcohol reducing bacteria. Further improvements could be achieved if the acetate-producing EEO was minimized and limitations of ethanol and CO2 were prevented.

Protein hydrolysis and fermentation under methanogenic and acidifying conditions

“…Interestingly, the large difference between the hydrolysis and acidification rates offers the possibility to avoid the degradation of amino acid and design the reactor such that they can be recovered. For instance, valine, leucine and iso-leucine are important substrates for branched fatty acids formation such as iso-butyrate, iso-valerate and iso-caproate that can be harvested from fermenting protein-rich waste streams for potential branched chain elongation [41].…”

Higher Abundance of Sediment Methanogens and Methanotrophs Do Not Predict the Atmospheric Methane and Carbon Dioxide Flows in Eutrophic Tropical Freshwater Reservoirs

“…This fermenter community diversity strongly suggests that plenty of fermentative subproducts are available and indicates the occurrence of syntrophic associations. In fact, the Anaerolineae class may form syntrophic cooperation with methanogens ( Liang et al, 2015 ), which were also observed for UCG-001 ( de Leeuw et al, 2019 ). Similarly, Syntrophorhabdus , Syntrophus , and Smithella spp., from the Deltaproteobacteria class, and Caldisericum spp., from Caldisericia class, present in the same brown network, have demonstrated this syntrophic potential previously ( Mountfort et al, 1984 ; Guyot and Brauman, 1986 ; Liu et al, 1999 ; Qiu et al, 2008 ; Szafranek-Nakonieczna et al, 2019 ), although a direct interaction with Methanobacterium spp.…”

Three Novel Clostridia Isolates Produce n-Caproate and iso-Butyrate from Lactate: Comparative Genomics of Chain-Elongating Bacteria

“…Currently, n -caproate is mainly produced from vegetable oils such as palm kernel oil [ 8 ], though it can be produced from more sustainable feedstocks such as agro-industrial waste by anaerobic fermentation and microbial chain elongation [ 9 , 10 ]. Compared to linear carboxylates, branched-chain carboxylates such as iso -butyrate are of special interest for alternative applications due to their different physical properties, including higher viscosity, higher oxidative stability, and a lower boiling point [ 11 ]. For example, iso -butyrate can be used for the synthesis of texanol, which is a widely used coalescent for latex paints [ 2 ].…”