Project description:Mitigation of N2O-emissions from soils is needed to reduce climate forcing by food production. Inoculating soils with N2O-reducing bacteria would be effective, but costly and impractical as a standalone operation. Here we demonstrate that digestates obtained after biogas production may provide a low-cost and widely applicable solution. Firstly, we show that indigenous N2O-reducing bacteria in digestates grow to high levels during anaerobic enrichment under N2O. Gas kinetics and meta-omic analysis show that the N2O respiring organisms, recovered as metagenome-assembled genomes (MAGs) grow by harvesting fermentation intermediates of the methanogenic consortium. Three digestate-derived denitrifying bacteria were obtained through isolation, one of which matched the recovered MAG of a dominant Dechloromonas-affiliated N2O reducer. While the identified N2O-reducers encoded genes required for a full denitrification pathway and could thus both produce and sequester N2O, their regulatory traits predicted that they act as N2O-sinks in the current system. Secondly, moving towards practical application, we show that these isolates grow by aerobic respiration in digestates, and that fertilization with these enriched digestates reduces N2O emissions. This shows that the ongoing implementation of biogas production in agriculture opens a new avenue for cheap and effective reduction of N2O emissions from food production.
Project description:The majority of potent greenhouse gas nitrous oxide (N2O) emissions originate from microbially mediated reactions. The enzyme N2O reductase is the only known biological N2O sink and has evolved in two phylogenetically distinct lineages (clades I and II). Clade II is of particular interest for biotechnology as it is often associated with non-denitrifying N2O reducers. In this study, Laureni et al. investigated the environmental conditions that select for clade II. To do so, we enriched two N2O-respiring communities at low dilution rates, under both electron donor (acetate) and electron acceptor (N2O) limitations, in order to assess the impact of substrate affinity and N2O cytotoxicity on community assembly. We used a combination of genome-resolved metagenomics and shotgun metaproteomics to identify the taxonomy and metabolic potential of the steady-state community members. Corresponding author: Michele Laureni, contact: m.laureni@tudelft.nl