Resource allocation explains lactic acid production in mixed‐culture anaerobic fermentations

Abstract

Lactate production in anaerobic carbohydrate fermentations with mixed cultures of microorganisms is generally observed only in very specific conditions: the reactor should be run discontinuously and peptides and B vitamins must be present in the culture medium as lactic acid bacteria (LAB) are typically auxotrophic for amino acids. State‐of‐the‐art anaerobic fermentation models assume that microorganisms optimise the adenosine triphosphate (ATP) yield on substrate and therefore they do not predict the less ATP efficient lactate production, which limits their application for designing lactate production in mixed‐culture fermentations. In this study, a metabolic model taking into account cellular resource allocation and limitation is proposed to predict and analyse under which conditions lactate production from glucose can be beneficial for microorganisms. The model uses a flux balances analysis approach incorporating additional constraints from the resource allocation theory and simulates glucose fermentation in a continuous reactor. This approach predicts lactate production is predicted at high dilution rates, provided that amino acids are in the culture medium. In minimal medium and lower dilution rates, mostly butyrate and no lactate is predicted. Auxotrophy for amino acids of LAB is identified to provide a competitive advantage in rich media because less resources need to be allocated for anabolic machinery and higher specific growth rates can be achieved. The Matlab™ codes required for performing the simulations presented in this study are available at https://doi.org/10.5281/zenodo.4031144.

Improving lactic acid production via bio-augmentation with acid-tolerant isolates from source-sorted organic household waste

“…Thus, pretreatment is usually needed to hydrolyze the complex organic matters due to incapability of most LAB to directly metabolize oligosaccharides [5]. Moreover, sterilization of SSOHW is required to avoid contamination of indigenous bacteria, making the fermentation process intricate and costly [6]. Therefore, mix-culture fermentation is an attractive approach, considering its intrinsic economic and operational advantage [6,7].…”

“…Moreover, sterilization of SSOHW is required to avoid contamination of indigenous bacteria, making the fermentation process intricate and costly [6]. Therefore, mix-culture fermentation is an attractive approach, considering its intrinsic economic and operational advantage [6,7].…”

Dynamic metagenome‐scale metabolic modeling of a yogurt bacterial community

“…Furthermore, proteome allocation was implemented to constrain reaction fluxes of the central carbon metabolism (Regueira et al, 2021; Zeng & Yang, 2020). Proteome was divided into sectors of inflexible housekeeping ( Q ), anabolism ( A ), transportation ( T ), catabolism ( C ), and the free sector.…”

Engineering the outcome of cofermentation processes by altering the feedstock sugar-to-protein ratio

“…It was hypothesised that the increase in STP ratio promotes CE processes as glucose is converted into adequate electron donor compounds, such as ethanol and/or lactate, 11,24 while generating a surplus of reducing power. 25 These alternative end products are, in fact, suitable substrates for the elongation of acetic and propionic acid to n-butyric and n-valeric acid, respectively.…”