Trace Elements Induce Predominance among Methanogenic Activity in Anaerobic Digestion

Area of Science:

• * Biogeochemistry and Microbial Ecology
• * Environmental Biotechnology
• * Anaerobic Digestion Processes

Background:

• * Trace elements (TEs) are vital for enzyme function and microbial metabolism in anaerobic digestion (AD).
• * TE deficits can disrupt AD processes, but the specific microbial responses and metabolic adaptations remain unclear.
• * Understanding TE roles is crucial for optimizing methane production and process stability.

Purpose of the Study:

• * To investigate microbial community dynamics and process changes under trace element deprivation in anaerobic digesters.
• * To elucidate the metabolic mechanisms and adaptation strategies of microbial communities facing TE deficits.
• * To determine the impact of specific TE deficiencies (Ni, Co, Mo, W) on methanogen activity and community structure.

Main Methods:

• * Operation of two identical lab-scale continuous stirred tank reactors (CSTRs) with distiller's grains as feedstock.
• * One reactor received TE supplementation (Co, Mo, Ni, W) and iron, while the other experienced TE omission and reduced iron.
• * Monitoring of process parameters (biogas, solids, VFAs, TAN, pH) and microbial community composition/activity (mcrA transcripts).

Main Results:

• * TE depletion led to increased hydrogen sulfide, total ammonia nitrogen, and acetate concentrations, despite stable methane yield.
• * Methanosarcina and Methanoculleus dominated both reactors, but their activity ratio shifted under TE deprivation.
• * Nickel, cobalt, molybdenum, tungsten, and manganese decline significantly impacted the balance of mcrA transcripts, favoring hydrogenotrophic methanogenesis.

Conclusions:

• * Trace element supply is critical for maintaining the activity of versatile methanogens like Methanosarcina.
• * TE deprivation favors hydrogenotrophic methanogens (e.g., Methanoculleus) due to lower requirements for nickel-dependent enzymes and cofactors.
• * Specific TE deficiencies significantly influence the structure and function of anaerobic digester microbial communities, impacting metabolic pathways.