Food waste disposal and transportation of commodity chemicals to the point-of-need are substantial challenges in military environments. Here, we propose addressing these challenges via the design of a microbial consortium for the fermentation of food waste to hydrogen. First, we simulated the exchange metabolic fluxes of monocultures and pairwise co-cultures using genome-scale metabolic models on a food waste proxy. We identified that one of the top hydrogen producing co-cultures comprised Clostridium beijerinckii NCIMB 8052 and Yokenella regensburgei ATCC 43003. A consortium of these two strains produced a similar amount of hydrogen gas and increased butyrate compared to the C. beijerinckii monoculture, when grown on an artificial garbage slurry. Increased butyrate production in the consortium can be attributed to cross-feeding of lactate produced by Y. regensburgei. Moreover, exogenous lactate promotes the growth of C. beijerinckii with or without a limited amount of glucose. Increasing the scale of the consortium fermentation proved challenging, as two distinct attempts to scale-up the enhanced butyrate production resulted in different metabolic profiles than observed in smaller scale fermentations. Though the genome-scale metabolic model simulations provided a useful starting point for the design of microbial consortia to generate value-added products from waste materials, further model refinements based on experimental results are required for more robust predictions.
Separations
in biological systems remain a challenging problem
and can be particularly so in the case of biofuels, where purification
can use a significant fraction of the energy content of the fuel.
For small-molecule biofuels like ethanol, reverse osmosis (RO) membranes
show promise as passive purifiers, in that they allow uncharged small
molecules to pass through while blocking most other components of
the growth medium. Here, we examine the use of RO membranes in developing
biohybrid fuel cells, closely examining the case where a direct ethanol
fuel cell (DEFC) is coupled with an ongoing yeast fermentation across
an RO membrane. We show that, contrary to initial good performance,
the acetic acid produced by the DEFC readily diffuses back across
the RO membrane and kills the fermentation after a few days. We introduce
an amelioration chamber where the acetic acid is converted to acetate
ions. The RO membrane rejects the acetate ions due to their charge,
preventing acetic acid buildup in the fermentation. We also show that
some small, charged components of the fermentation such as amino acids
are imperfectly rejected by RO membranes. Because of the high sensitivity
of DEFCs to low concentrations (10s of μM) of amino acids, even
a very slow diffusion of amino acids across the RO membranes can limit
biohybrid fuel cell lifetimes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.