(138c) A Unified Inorganic-Biological System to Produce Energy-Efficient Food with Flavors

Two major challenges presently confronting the world are to meet the global increase in food demand and mitigate carbon dioxide (CO₂) emissions [1]. Over the last decades, the biological route employing autotrophs (plants, microalgae, and certain bacteria) to mitigate CO₂ and simultaneously produce high-valued products like, biofuels, bioethanol, bioplastic, and succinic acid has been thoughtfully considered in various studies [2, 3]. Despite these efforts, the economic feasibility to achieve a high biomass yield, %conversion, and productivity utilizing autotrophs under high CO₂ stress at the production scale remains a major obstacle [4, 5]. Also, the recent advancements in breeding and genetic engineering to ensure high solar-to-biomass conversion at elevated CO₂ levels have resulted in only a mediocre performance[6]. This requires delineating biological routes with novel approaches to providing a sustainable solution for satisfying global food demand and CO₂ mitigation.

Artificial photosynthesis can potentially overcome the limitations of lower photosynthesis/chemosynthesis efficiency and poor CO₂ reduction associated with autotrophs/chemotrophs, resulting in food with high nutritional value [7]. In recent years, different researchers have investigated and demonstrated the conversion of CO₂ and H₂O into reduced compounds such as carbon monoxide (CO), acetate, formate, hydrogen (H₂), and methanol [1]. Out of these, via bacterial fermentation, CO₂, CO, and H₂ can be transformed into fuels and chemicals. However, its economic feasibility at a large scale remains questionable [8]. The utilization of formate/methanol as a carbon substrate during fermentation is not energetically encouraging and, results in poor growth due to the formation of toxic formaldehyde as an intermediate [8, 9]. However, acetate (CH3COO^–) that can be produced electrochemically has been found to be utilized as a carbon source by many microorganisms [8, 10].

Acetate has been recently considered as a potential alternative carbon substrate during fermentation for the following reasons: (1) Easy to feed at high concentrations or in pure form at a very low dilution rate due to high water solubility of acetic acid and acetate salts, results in easy mass transfer into the culture broth dring fermentation (2) utilization of acetate from culture results in an increase in pH that can be used as an online process parameter to monitor and control acetate feeding (3) Acetate is a non-reducing compound and hence, does not result in Maillard reactions like glucose during sterilization, fermentation, or downstream processing (4) Most of the industrially important food-like biomass-producing microorganisms are capable to grow on acetate as the sole carbon source and (5) Acetate metabolism result in acetyl-CoA as well as glyoxylate/tricarboxylic acid (TCA) cycle intermediates that can be utilized to synthesize different high value-added bio-products [10, 11].

In the present work, hybrid inorganic-bio-based systems were conceptualized and proposed as an efficient route to transform acetate into food. The work involves growing mixed consortium consisting of engineered yeast, fungus, algae, and bacteria in the dark to provide biomass with tailored nutrient composition with desired flavors. Shake flask studies were conducted to adaptively evolve the pure strains capable of growing and utilizing high acetate concentrations of 1.5% w.w^-1. To optimize culture minimal salt medium (MSM), Plackett-Burman screening in conjunction with response surface methodology (RSM) was utilized. The optimized MSM with the mixed consortium was grown in a 1 L fermenter to maximize biomass yield, followed by downstream processing. With optimized agitation and aeration of 800 RPM and 1 vvm, respectively followed by centrifugation to harvest biomass, a 4 g.L^-1 of biomass yield was obtained in 24 h. Optimized conditions were scaled-up to a 20-L pilot scale bioreactor to generate industrially relevant data. This is the first demonstration of the technology that allows for conceiving a newer way of producing food (without the use of conventional agriculture) with tailored nutritional profiles in controlled conditions.