nZVI Impacts Substrate Conversion and Microbiome Composition in Chain Elongation From D- and L-Lactate Substrates

Abstract

Medium-chain carboxylates (MCC) derived from biomass biorefining are attractive biochemicals to uncouple the production of a wide array of products from the use of non-renewable sources. Biological conversion of biomass-derived lactate during secondary fermentation can be steered to produce a variety of MCC through chain elongation. We explored the effects of zero-valent iron nanoparticles (nZVI) and lactate enantiomers on substrate consumption, product formation and microbiome composition in batch lactate-based chain elongation. In abiotic tests, nZVI supported chemical hydrolysis of lactate oligomers present in concentrated lactic acid. In fermentation experiments, nZVI created favorable conditions for either chain-elongating or propionate-producing microbiomes in a dose-dependent manner. Improved lactate conversion rates and n-caproate production were promoted at 0.5–2 g nZVI⋅L–1 while propionate formation became relevant at ≥ 3.5 g nZVI⋅L–1. Even-chain carboxylates (n-butyrate) were produced when using enantiopure and racemic lactate with lactate conversion rates increased in nZVI presence (1 g⋅L–1). Consumption of hydrogen and carbon dioxide was observed late in the incubations and correlated with acetate formation or substrate conversion to elongated products in the presence of nZVI. Lactate racemization was observed during chain elongation while isomerization to D-lactate was detected during propionate formation. Clostridium luticellarii, Caproiciproducens, and Ruminococcaceae related species were associated with n-valerate and n-caproate production while propionate was likely produced through the acrylate pathway by Clostridium novyi. The enrichment of different potential n-butyrate producers (Clostridium tyrobutyricum, Lachnospiraceae, Oscillibacter, Sedimentibacter) was affected by nZVI presence and concentrations. Possible theories and mechanisms underlying the effects of nZVI on substrate conversion and microbiome composition are discussed. An outlook is provided to integrate (bio)electrochemical systems to recycle (n)ZVI and provide an alternative reducing power agent as durable control method.

Designing a Selective n-Caproate Adsorption–Recovery Process with Granular Activated Carbon and Screening of Conductive Materials in Chain Elongation

“…The chain elongation lag phase was decreased to <2 days with GAC and NF compared to experiments with stainless steel (SS) or without conductive materials (>4 days). In line with previous studies, n -butyrate was the main product of batch lactate fermentation, whereas mainly MCC are produced in continuous systems . However, total propionate production was consistently lower (∼30%) when any of the conductive materials was present resulting in higher selectivities for chain elongation products ( n -butyrate, isobutyrate, or n -caproate).…”

“…The electron balance showed that part of the lactate oligomers present in the concentrated lactic acid solution were used for fermentation (Figure A). Lactate monomers and acetate comprised about 68% of the electrons in the added substrate (total lactate and acetate).…”

“…Concentrated lactic acid was a mixture of lactate monomers (∼64%) and oligomers ( e.g. , lactyl lactate) containing mainly l -lactic acid (≥97%, as reported by VWR). Incubation were performed in 500 mL Scotch bottles (300 mL liquid volume) with the headspace connected directly to a gas flow measuring device (AMPTS II, Bioprocess Control).…”

Glucose oxidase as an alternative to antibiotic growth promoters improves the immunity function, antioxidative status, and cecal microbiota environment in white-feathered broilers

“…Correspondingly, substantial evidence highlighted that inosine has broad antiinflammatory and immunomodulatory properties (Haskó et al, 2000(Haskó et al, , 2004da Rocha Lapa et al, 2012). The second noticed genus, Oscillibacter, whose clade was regarded as a potential n-butyrate producer (Gophna et al, 2017;Contreras-Dávila et al, 2021), was placed in the family Ruminococcaceae. In recent studies, this family showed a high correlation with the increase in bodyweight and tight junction protein expression for birds (Dai et al, 2021;Farkas et al, 2022).…”

Microbial Recycling of Polylactic Acid Food Packaging Waste into Carboxylates via Hydrolysis and Mixed-Culture Fermentation

“…We hypothesize that such lactic acid derived from PLA can also be fermented into other carboxylates like acetate and n-buty-rate by various known bioprocesses [ 9 ]. Therefore, short-chain carboxylates could be chain-elongated using the remaining lactate up to medium-chain carboxylates once the various bioprocesses are combined within a bioreactor [ 11 , 23 ].…”