21 independent full-scale biogas digesters with manures as materials

The microbially mediated anaerobic digestion (AD) represents an efficient technology for the treatment of organic waste along with biogas harvest. However, less is known on the primary driving factor of bacterial community structure, the characteristics of bacterial co-occurring network, and the mechanisms of community assembly in the full-scale AD systems. To address these questions, we collected sludge samples from 20 independent full-scale biogas digesters with cattle or swine manures as raw materials, and investigated the variations of bacterial communities and co-occurring networks using 16S rRNA amplicon pyrosequencing technique. The results showed that substrate type was the primary factor shaping bacterial community structure. Cattle manure increased bacterial diversity, accompanied by the higher relative abundance of minor genera, while Clostridium sensu stricto predominated in swine manure digesters. NH4+-N/Phosphate (N:P) may be the main factor controlling the stability and efficiency of manure AD systems, and the performance of cattle manure digesters may also be affected by COD and COD/NH4+-N (C:N). In addition, the abundant OTUs in both types of digesters were less co-occurred with other OTUs. However, the bacterial co-occurring networks were enhanced by cattle manure, the enriched specific populations could be responsible for the complete hydrolysis of recalcitrant lignocellulose. Null model analysis suggested that deterministic factor may be more important in the process of microbial community assembly, during which interspecies interactions and environmental selections may contribute differently. This study provides new insights into the effect of substrate on microbial communities and the mechanism of community assembly in full-scale anaerobic digesters.