88 Chapter 3 Distinct substrate loading defines methanotrophic community structures with repercussions on the nitrogen cycle We proceeded to disentangle the abundance and contributions of the methanotrophic populations in these communities. Despite the absence of oxygen via air supply and high amounts of reducing sulfide and nitrate, a variety of MOB were enriched in both systems. Type I MOB belonging to Methylomonadaceae (Gammaproteobacteria) showed the highest abundance in nearly all systems and niches (Figure 3A and Supplementary Figure 5). In the eutrophic system, we retrieved between 0.5 % (bioreactor month 3) to as much as 38.6 % (biofilm month 10) bacterial ASVs reads of this taxon (Figure 3A and Supplementary Table 2). In the oligotrophic system, we recovered between 1.5 % (bioreactor month 3) and 16.8 % (biofilm month 7) of Methylomonadaceae ASV reads (Figure 3A and Supplementary Table 2). The oligotrophic system appeared to have a slightly less abundant (ASV counts), yet more diverse, community of methanotrophs compared to the eutrophic one, including more representatives of Crenothrix, Methylobacter, or Methylomonadaceae methanotrophs for which no genus could be assigned based on 16S rRNA gene sequence (Figure 3A). For both the eutrophic and oligotrophic systems, the MOB community was more abundant in the biofilm than in the bioreactor (double the amount of ASV counts) (Figure 3A, Supplementary Figure 5 and Supplementary Table 1 and 2), whereas the anaerobic methanotrophic archaeon “Ca. Methanoperedens” thrived better in the oligotrophic bioreactor, being present both in the bioreactor suspension and the biofilm (Supplementary Table 3, Supplementary Figure 7). In the oligotrophic system, “Ca. Methanoperedens BLZ2” (with different 16S rRNA gene ASVs identified) contributed to more than 89.2% of the total archaeal ASV reads recovered from month 7 onwards and sustained its presence over time, with 99.4% of the archaeal 16S rRNA gene amplicon reads in month 15.5 in the bioreactor (matching as much as 21 % of the total metagenomic reads for the same month and system) (Supplementary Figure 5 and Supplementary Table 3). On the contrary, the eutrophic system showed only traces of “Ca. Methanoperedens” from month
RkJQdWJsaXNoZXIy MTk4NDMw