Abstract
BackgroundThe molecular machinery of the complex microbiological cell factory of biomethane production is not fully understood. One of the process control elements is the regulatory role of hydrogen (H2). Reduction of carbon dioxide (CO2) by H2 is rate limiting factor in methanogenesis, but the community intends to keep H2 concentration low in order to maintain the redox balance of the overall system. H2 metabolism in methanogens becomes increasingly important in the Power-to-Gas renewable energy conversion and storage technologies.ResultsThe early response of the mixed mesophilic microbial community to H2 gas injection was investigated with the goal of uncovering the first responses of the microbial community in the CH4 formation and CO2 mitigation Power-to-Gas process. The overall microbial composition changes, following a 10 min excessive bubbling of H2 through the reactor, was investigated via metagenome and metatranscriptome sequencing. The overall composition and taxonomic abundance of the biogas producing anaerobic community did not change appreciably 2 hours after the H2 treatment, indicating that this time period was too short to display differences in the proliferation of the members of the microbial community. There was, however, a substantial increase in the expression of genes related to hydrogenotrophic methanogenesis of certain groups of Archaea. As an early response to H2 exposure the activity of the hydrogenotrophic methanogenesis in the genus Methanoculleus was upregulated but the hydrogenotrophic pathway in genus Methanosarcina was downregulated. The RT-qPCR data corroborated the metatranscriptomicResultsH2 injection also altered the metabolism of a number of microbes belonging in the kingdom Bacteria. Many Bacteria possess the enzyme sets for the Wood-Ljungdahl pathway. These and the homoacetogens are partners for syntrophic community interactions between the distinct kingdoms of Archaea and Bacteria.ConclusionsExternal H2 regulates the functional activity of certain Bacteria and Archaea. The syntrophic cross-kingdom interactions in H2 metabolism are important for the efficient operation of the Power-to-Gas process. Therefore, mixed communities are recommended for the large scale Power-to-Gas process rather than single hydrogenotrophic methanogen strains. Fast and reproducible response from the microbial community can be exploited in turn-off and turn-on of the Power-to-Gas microbial cell factories.
Highlights
The molecular machinery of the complex microbiological cell factory of biomethane production is not fully understood
We demonstrated earlier that by the introduction of H 2-producing bacteria into a natural biogas-generating consortium appreciably increased the efficacy of biogas production both in batch fermentations and in scaled-up continuous Anaerobic digestion (AD) [14]
A constant value of VOA/TIC is a reliable indicator of a stable mesophilic fermentation process [32]
Summary
The molecular machinery of the complex microbiological cell factory of biomethane production is not fully understood. Anaerobic digestion (AD) of organic wastes and byproducts by specialized microbial communities and the concomitant biogas production is an environmentally attractive bioenergy production technology. Biogas provides environmental benefits with regard to waste treatment, pollution reduction, production of CO2-neutral renewable energy and the improvement of economy of agricultural practices through the recycling of plant nutrients and replacing artificial fertilizers [2]. While the main microorganisms and mechanisms involved in the methane producing anaerobic microbial cell factories are fairly well-known, the regulation and management of the overall process is far from being fully understood [4, 5]. Despite the industrial-economic importance of the underlying microbiological events, little is known about the roles, networking interactions of the microorganisms and the regulatory mechanisms of the methane production. In the absence of terminal electron acceptors such as nitrate, oxygen or sulfate, the methanogenic conversion of organic matter is an essential feature of many ecosystems [8]
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