Improving process stability and kinetics of anaerobic biowaste digestion by promoting direct interspecies electron transfer among syntrophic microbial consortia

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Microbial conversion of organic matter to renewable energy in form of methane is a proven and widespread strategy for effective waste management. In such methane-producing environments, electrical connected bacteria and archaea perform direct interspecies electron transfer (DIET) as alternative syntrophic mechanism to interspecies hydrogen or formate transfer (IHT). However, fundamental aspects of the microbial ecology concerning DIET are still unclear, in particular, its significance for biogas production remains to be elucidated. To date, studies largely focused on DIET in methanogenic co-cultures of very few model organisms associated with mesophilic upflow anaerobic sludge blanket (UASB) reactors treating wastewaters. We intend to generate a more widely applicable knowledge of structure-function relationships within syntrophic core communities in mesophilic and thermophilic digesters by integrating cutting-edge molecular tools such as the 16S rRNA approach, metagenomics and transcriptomics with cultivation-based techniques to ultimately induce higher process stability and efficiency of anaerobic digestion (AD). Key objectives are the identification of novel organisms capable of DIET and to understand the genetic mechanisms underlying DIET with an emphasis on biowaste-digesting biogas plants that substantially differ from mesophilic UASB reactors in terms of reactor setup, mode of operation, temperature and substrate composition. We suggest that DIET is a co-occurring alternative to IHT common in AD. To our knowledge, the proposed project will target DIET for the first time in both thermophilic and mesophilic systems. We further aim to determine potential substrates metabolized during DIET focused on syntrophic propionate- and butyrate-oxidizing consortia that are of vital importance for the anaerobic breakdown of organic matter. Metagenomics will be used to reconstruct metabolic capabilities along with transcriptomics to reveal expression patterns associated with DIET. A process that circumvents the production of hydrogen, which accumulation can be critical to overall process functioning, may be beneficial for the stability of AD. Therefore, we will specifically enrich syntrophic consortia performing DIET and investigate physiological advantages over IHT. The anticipated results will represent an imperative step to exploit the full potential of AD. Given the fact that DIET is widely distributed in anoxic environments and the general need for efficient transfer of metabolites in cooperating communities our results will be relevant also to other fields of research such as reducing greenhouse gas emissions from methanogenic environments and bio-electrochemical systems where electrical connected microbes are implicated.