Modeling microbial interactions in lactate-driven dark fermentation systems using metabolic models

Abstract

Dark fermentation (DF) is a promising alternative for biohydrogen (H₂) production using agro-industrial wastes, contributing to clean energy generation and waste management. However, industrial scaling of DF is hindered by instability issues, particularly due to microbial interactions, such as competition between lactic acid bacteria (LAB) and hydrogen-producing bacteria (HPB). While LAB are often considered inhibitors of H₂ production, recent studies suggest their potential role in lactate-driven DF, where HPB utilizes lactate and acetate as alternative substrates. Despite this, the mechanisms regulating LAB-HPB interactions are still a research gap. This study developed a simplified metabolic model to describe a LAB-HPB consortium performing lactate-driven DF, focusing on LAB and HPB interactions. The model was constructed based on previous models and experimental data, guided by taxonomic and functional analysis. Flux Balance Analysis (FBA) was used for model calibration. Key enzymes and electron bifurcation mechanisms involved in H₂ production were identified. The model predicted that H₂ production gradually declined as LAB fractions increased, with a modest reduction below 0.3 (maintaining favorable production levels) and complete inhibition occurring above 0.85. These findings highlight the importance of optimizing the HPB-to-LAB ratio and understanding their metabolic interactions to enhance H₂ production. Future research should validate the model predictions and explore additional conditions to improve DF efficiency.