114 Chapter 4 indicated that the community removed residual nitrate (834 μM) via denitrification and DNRA for several weeks. Biomass decay was evident from ammonium concentrations (0-500 μM), the visual increase in reactor turbidity and, to a degree, change of granule color from red to black, until the end of the experiment. The composition of the bioreactor microbial community was investigated via a time series of metagenomic sequencing (Figure 1, G0-G5). In a previous study with this bioreactor, community members included several proteobacteria, “Ca. Kuenenia stuttgartiensis”, “Ca. Scalindua brodae”, “Ca. Methanoperedens nitroreducens”, “Ca. Methylomirabilis” species, and a novel bacterium within the Nitrospirota phylum, “Ca. Nitrobium versatile”, potentially linking sulfur and nitrogen cycling (Arshad et al., 2017; Zecchin et al., 2018; Umezawa et al., 2020, 2021). Co-assembly of eight samples resulted in 30 high (>90% complete, <5% contaminated) and 29 medium (>50% complete, <10% contaminated) quality metagenome-assembled genomes (MAGs) (Figure 2). We will first introduce the most dominant members and, in the next section, we will discuss their change in abundance over time. The only archaeon detected in the bioreactor was “Ca. Methanoperedens nitroreducens” (MAG 36), a nitrate-reducing anaerobic methanotroph. Bacteria were much more diverse and represented by five MAGs affiliated to candidate phyla (AABM5-125-24, ARS69, FEN-1099, GWC2-55-46, OLB16), two to Acidobacteriota, one to Actinobacteriota, one to Armatimonadota, eleven to Bacteroidota, six to Chloroflexota, one to Cyanobacteria, two to Methylomirabilota, two to Myxococcota, one to Nitrospirota, one to Omnitrophota, five to Planctomycetota, and twenty to Proteobacteria.
RkJQdWJsaXNoZXIy MTk4NDMw