These findings are not surprising, as human fecal bacteria has also been noted in concrete biofilms in previous studies [7–9]. Sections of wastewater pipes exhibit conditions that are favorable for the establishment of oxic zones, e.g., at the top of the pipe (TP). In fact, the dominant TP biofilm members were associated with aerobic and facultative anaerobic bacteria (e.g. Thiobacillus Acidiphilium Xanthomonas Bradyrhizobium). The biofilms did not contain a significant presence of photosynthetic organisms (e.g. Cyanobacteria), which dominated biofilms in
concrete corroded city-surface structures [10]. The latter is supported by the low number of genes assigned to the photosynthesis Lorlatinib subsystems in our metagenome libraries ( Additional file 1, Vismodegib Figure S1). Taxonomic analysis based on annotated proteins show two distinct archaeal communities (Figure 1). The BP biofilm was dominated by the classes Methanomicrobia (55%), Thermococcus (10%) and Thermoprotei (8%). The classes Methanomicrobia (38%) and Thermoprotei (17%) were also abundant in the TP site although Halobacteria (15%) and Thaumarchaeota (7%) were also abundant. Members of the Thaumarchaeota phylum are chemolithoautotrophic
ammonia-oxidizers, which suggest that they may be playing a role in the nitrogen cycle in wastewater concrete biofilms [35]. Halobacteriales have been previously reported in wastewater sludge GSK872 and may suggest the presence of alkaline hypersaline microenvironments in wastewater concrete biofilms [36]. The anaerobic niches in the wastewater pipe provide
conditions for methanogenesis as suggested by the annotated sequences associated with genera ADAMTS5 such as Methanospirillum Methanobrevibacter Methanosphaera Methanosaeta Methanosarcina, and Methanococcoides[37]. However, the more favourable anaerobic conditions at the bottom of the pipe provide better conditions for this process. Indeed, there are a higher percentage of annotated sequences related to methanogenesis in the BP (69%) than in TP metagenomes (47%). Conversely, more methanotrophic and methylotrophic bacteria proteins were present in the TP (3.7%) than in BP biofilm (1.8%). Specifically, many of the sequences were related to proteins affiliated with Methylibium Methylobacillus Methylobacterium Methylocella Methylococcus, and Methylacidiphilum. The dominant annotated methane-oxidizing bacteria in the TP biofilm were affiliated with Methylocella silvestris, a moderately acidophilic (pH values between 4.5 and 7) and mesophilic species [38]. In general, our analysis identified microorganisms associated with one-carbon compound pathways (e.g. methanogenesis, methanotrophs and methylotrophs), although the importance of these metabolic processes in wastewater pipes remains unknown.