title: Trace Elements Induce Predominance among Methanogenic Activity in Anaerobic Digestion.
abstract: Trace elements (TE) play an essential role in all organisms due to their functions in enzyme complexes. In anaerobic digesters, control, and supplementation of TEs lead to stable and more efficient methane production processes while TE deficits cause process imbalances. However, the underlying metabolic mechanisms and the adaptation of the affected microbial communities to such deficits are not yet fully understood. Here, we investigated the microbial community dynamics and resulting process changes induced by TE deprivation. Two identical lab-scale continuous stirred tank reactors fed with distiller's grains and supplemented with TEs (cobalt, molybdenum, nickel, tungsten) and a commercial iron additive were operated in parallel. After 72 weeks of identical operation, the feeding regime of one reactor was changed by omitting TE supplements and reducing the amount of iron additive. Both reactors were operated for further 21 weeks. Various process parameters (biogas production and composition, total solids and volatile solids, TE concentration, volatile fatty acids, total ammonium nitrogen, total organic acids/alkalinity ratio, and pH) and the composition and activity of the microbial communities were monitored over the total experimental time. While the methane yield remained stable, the concentrations of hydrogen sulfide, total ammonia nitrogen, and acetate increased in the TE-depleted reactor compared to the well-supplied control reactor.MethanosarcinaandMethanoculleusdominated the methanogenic communities in both reactors. However, the activity ratio of these two genera was shown to depend on TE supplementation explainable by different TE requirements of their energy conservation systems.Methanosarcinadominated the well-supplied anaerobic digester, pointing to acetoclastic methanogenesis as the dominant methanogenic pathway. Under TE deprivation,Methanoculleusand thus hydrogenotrophic methanogenesis was favored althoughMethanosarcinawas not overgrown byMethanoculleus. Multivariate statistics revealed that the decline of nickel, cobalt, molybdenum, tungsten, and manganese most strongly influenced the balance ofmcrAtranscripts from both genera. Hydrogenotrophic methanogens seem to be favored under nickel- and cobalt-deficient conditions as their metabolism requires less nickel-dependent enzymes and corrinoid cofactors than the acetoclastic and methylotrophic pathways. Thus, TE supply is critical to sustain the activity of the versatile high-performance methanogenMethanosarcina.
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research - UFZ Leipzig, Germany.
authors.forename: Babett
authors.initials: B
authors.lastname: Wintsche
authors.affiliation: Department of Applied Ecology and Phycology, University of Rostock Rostock, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Glaser
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research - UFZ Leipzig, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Sträuber
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research - UFZ Leipzig, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Centler
authors.affiliation: Department of Biochemical Conversion, Deutsches Biomasseforschungszentrum - DBFZ Leipzig, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Liebetrau
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research - UFZLeipzig, Germany; German Centre for Integrative Biodiversity Research (iDiv)Leipzig, Germany.
authors.forename: Hauke
authors.initials: H
authors.lastname: Harms
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research - UFZ Leipzig, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Kleinsteuber
keywords: Methanoculleus; Methanosarcina; T-RFLP; amplicon sequencing; biogas reactor; mcrA; methanogenesis