Redirecting carbon and electron flow in methanogenic laboratory scale anaerobic digestors with hypophosphite
In anaerobic digestion, formate is a central electron carrier linking primary and secondary fermentation to methanogenesis. Efforts to alter methane production have largely focused on directly targeting methanogens, while disruption of other trophic levels is underexplored. We recently demonstrated that hypophosphite is a naturally occurring inhibitor of formate exchange in syntrophic…
In anaerobic digestion, formate plays a crucial role as an electron carrier between the initial and later stages of fermentation, ultimately leading to methane production. Researchers have been exploring ways to modify methane output by targeting different parts of this process. A recent study found that the compound hypophosphite, which naturally inhibits formate exchange in synergistic methanogenic systems, could potentially alter methane production.
In a series of experiments using continuous up-flow anaerobic sludge blanket (UASB) columns fed with whey, the researchers discovered that applying 100 millimolar hypophosphite caused a temporary (lasting 17 days) decrease in methane production by 20% to 50%. During this period, the electron and carbon flow was redirected towards hydrogen and volatile fatty acids, such as propionate, butyrate, and branched-chain fatty acids, instead of acetate. This suggested that the syntrophic formate metabolism was disrupted.
After the methane production resumed after hypophosphite treatment, increasing hypophosphite concentrations to millimolar levels did not lead to another reduction in methane production. The researchers also performed 16S rDNA amplicon sequencing, which showed that hypophosphite treatment did not significantly change the composition of the microbiome. Additionally, methanogenic activity assays revealed a loss of formatotrophic methanogenic capacity in the hypophosphite-treated columns.
In summary, this study demonstrates that selectively inhibiting formate exchange between syntrophic methanogens and fermenters with hypophosphite can decouple the fermentative and methanogenic processes without altering the microbiome composition. The electron and carbon flow ultimately redirected through alternative electron carriers, such as hydrogen or acetate, during long-term treatment with hypophosphite.
These findings suggest that hypophosphite could be a useful tool in engineering anaerobic digestion systems for improved methane production.
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