Mixotrophic chain elongation with syngas and lactate as electron donors

Abstract

Feeding microbial communities with both organic and inorganic substrates can improve sustainability and feasibility of chain elongation processes. Sustainably produced H 2 , CO 2 , and CO can be co‐fed to microorganisms as a source for acetyl‐CoA, while a small amount of an ATP‐generating organic substrate helps overcome the kinetic hindrances associated with autotrophic carboxylate production. Here, we operated two semi‐continuous bioreactor systems with continuous recirculation of H 2 , CO 2 , and CO while co‐feeding an organic model feedstock (lactate and acetate) to understand how a mixotrophic community is shaped during carboxylate production. Contrary to the assumption that H 2 , CO 2 , and CO support chain elongation via ethanol production in open cultures, significant correlations ( p < 0.01) indicated that relatives of Clostridium luticellarii and Eubacterium aggregans produced carboxylates (acetate to n ‐caproate) while consuming H 2 , CO 2 , CO, and lactate themselves. After 100 days, the enriched community was dominated by these two bacteria coexisting in cyclic dynamics shaped by the CO partial pressure. Homoacetogenesis was strongest when the acetate concentration was low (3.2 g L −1 ), while heterotrophs had the following roles: Pseudoramibacter , Oscillibacter , and Colidextribacter contributed to n ‐caproate production and Clostridium tyrobutyricum and Acidipropionibacterium spp. grew opportunistically producing n ‐butyrate and propionate, respectively. The mixotrophic chain elongation community was more efficient in carboxylate production compared with the heterotrophic one and maintained average carbon fixation rates between 0.088 and 1.4 g CO 2 equivalents L −1 days −1 . The extra H 2 and CO consumed routed 82% more electrons to carboxylates and 50% more electrons to carboxylates longer than acetate. This study shows for the first time long‐term, stable production of short‐ and medium‐chain carboxylates with a mixotrophic community.

Evaluating the feasibility of medium chain oleochemical synthesis using microbial chain elongation

“…However, it could be alleviated if methyl ketone production was conducted in the context of a microbial community, where other functional guilds could recycle the CO2 (Baleeiro et al, 2023).…”

Formate-induced CO tolerance and methanogenesis inhibition in fermentation of syngas and plant biomass for carboxylate production

“…The syngas-adapted community used as inoculum for the batch cultures originated from two 1.0 L stirred-tank reactors that were being operated near atmospheric pressure (102 kPa) with continuous syngas recirculation (32% H 2 , 32% CO, 16% CO 2 , 2% ethylene, 2% He, and rest N 2 at 40 mL min −1 ) at a hydraulic retention time of 14 d, pH 6.0, and 32 ℃ [29]. Once a day, 71.4 mL of fermentation broth was harvested and 71.4 mL of fresh mineral medium (Additional file 1: Table S1) containing additionally 12 g L −1 acetate and 12 g L −1 lactate was fed.…”

A specific H2/CO2 consumption molar ratio of 3 as a signature for the chain elongation of carboxylates from brewer’s spent grain acidogenesis

“…Like acetate and ethanol, acetyl-CoA is a key metabolite in the CE process. Baleeiro et al (2019) , Baleeiro et al (2021) , and Baleeiro et al (2022) hypothesized to promote MCC production by combining syngas fermentation with biomass fermentation. Some studies showed that H 2 positively affects MCC production ( Steinbusch et al, 2011 ; Nzeteu et al, 2018 ).…”