CO2 fixation by anaerobic non-photosynthetic mixotrophy for improved carbon conversion

Abstract

Maximizing the conversion of biogenic carbon feedstocks into chemicals and fuels is essential for fermentation processes as feedstock costs and processing is commonly the greatest operating expense. Unfortunately, for most fermentations, over one-third of sugar carbon is lost to CO2 due to the decarboxylation of pyruvate to acetyl-CoA and limitations in the reducing power of the bio-feedstock. Here we show that anaerobic, non-photosynthetic mixotrophy, defined as the concurrent utilization of organic (for example, sugars) and inorganic (for example, CO2) substrates in a single organism, can overcome these constraints to increase product yields and reduce overall CO2 emissions. As a proof-of-concept, Clostridium ljungdahlii was engineered to produce acetone and achieved a mass yield 138% of the previous theoretical maximum using a high cell density continuous fermentation process. In addition, when enough reductant (that is, H2) is provided, the fermentation emits no CO2. Finally, we show that mixotrophy is a general trait among acetogens.

Heterologous Expression of the Clostridium carboxidivorans CO Dehydrogenase Alone or Together with the Acetyl Coenzyme A Synthase Enables both Reduction of CO 2 and Oxidation of CO by Clostridium acetobutylicum

“…High-performance liquid chromatography (HPLC) was used to measure metabolite concentrations in fermentation medium. Metabolites were detected using an Agilent HPLC instrument with a Bio-Rad Aminex HPX 87H column using a 5 mM H 2 SO 4 mobile phase and a flow rate of 0.5 ml/min (55).…”

Enhancing hydrogen‐dependent growth of and carbon dioxide fixation by Clostridium ljungdahlii through nitrate supplementation

“…The advent of genetic tools for the model acetogen Clostridium ljungdahlii (Köpke et al, 2010) provided an opportunity to divert flux away from acetate to more valuable molecules through metabolic engineering. To date, acetogens have been engineered to produce a variety of chemicals, including butanol (Köpke et al, 2010), butyrate (Ueki, Nevin, Woodard & Lovley, 2014), lactate (Iwasaki et al, 2017), and acetone (Hoffmeister et al, 2016;Jones et al, 2016).…”

Experimental Design to Improve Cell Growth and Ethanol Production in Syngas Fermentation by Clostridium carboxidivorans

“…While in the carbonyl branch, CO 2 is reduced to CO consuming two electrons. The CO and the methyl group formed in this first step of WL pathway are converted into 1 mol of acetyl-CoA [33][34][35]. Thereby, the glycolysis and WL are complementary pathways as CO 2 and electrons produced in the glycolysis are fully utilized by WL to produce one additional mol of acetyl-CoA increasing its yield by 50% in relation to glucose metabolism.…”