Abstract
Although microbial communities of anaerobic bioreactors have been extensively studied using DNA-based tools, there are still several knowledge gaps regarding the microbiology of the process, in particular integration of all generated data is still limited. One understudied core phylum within anaerobic bioreactors is the phylum Chloroflexi, despite being one of the most abundant groups in anaerobic reactors. In order to address the abundance, diversity and phylogeny of this group in full-scale methanogenic reactors globally distributed, a compilation of 16S ribosomal RNA gene sequence data from 62 full-scale methanogenic reactors studied worldwide, fed either with wastewater treatment anaerobic reactors (WTARs) or solid-waste treatment anaerobic reactors (STARs), was performed. One of the barriers to overcome was comparing data generated using different primer sets and different sequencing platforms. The sequence analysis revealed that the average abundance of Chloroflexi in WTARs was higher than in STARs. Four genera belonging to the Anaerolineae class dominated both WTARs and STARs but the core populations were different. According to the phylogenetic analysis, most of the sequences formed clusters with no cultured representatives. The Anaerolineae class was more abundant in reactors with granular biomass than in reactors with disperse biomass supporting the hypothesis that Anaerolineae play an important role in granule formation and structure due to their filamentous morphology. Cross-study comparisons can be fruitfully used to understand the complexity of the anaerobic digestion process. However, more efforts are needed to standardize protocols and report metadata information.
Highlights
Anaerobic digestion is an efficient biological process widely applied to treat solid organic waste and wastewater, where the organic matter can be converted into a renewable energy source known as biogas
As different primer pairs were used to generate sequences in the different investigations, we analyzed how this might affect the recovery of Chloroflexi populations, at different taxonomic levels, frequently found in methanogenic reactors
Despite the bias generated from using different hypervariable regions we found that the Anaerolineae class largely dominated in both solid-waste treatment anaerobic reactors (STARs) and wastewater treatment anaerobic reactors (WTARs) which was consistent with previous DNA based surveys (Rivière et al, 2009; Nelson et al, 2011; Bovio et al, 2019)
Summary
Anaerobic digestion is an efficient biological process widely applied to treat solid organic waste and wastewater, where the organic matter can be converted into a renewable energy source known as biogas. Chloroflexi has been reported as one of the most predominant phylum present in solid waste and wastewater treatment systems (Shu et al, 2015; Petriglieri et al, 2018; Bovio et al, 2019). The Anaerolineae class has been identified as one of the core microbial populations in full-scale anaerobic reactors (Nelson et al, 2011; St-Pierre and Wright, 2014; Bovio et al, 2019). From 12 isolated strains within the Anaerolineae class, five have been isolated from wastewater treatment anaerobic reactors (WTARs) and one from solid-waste treatment anaerobic reactors (STARs) (Sekiguchi et al, 2003; Yamada et al, 2006, 2007a; Sun et al, 2016). The ecological role of the Anaerolineae remains uncertain due to the scarcity of isolates and annotated genome sequences
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