Changes in the prokaryotic communities occurring along a two-stage anaerobic digestion system treating the organic fraction of solid waste

Two-stage anaerobic digestion is useful for recycling of the organic fraction of municipal solid waste and wastewater; the prokaryotic communities involved in this process were characterized using massive sequencing of 16S rRNA gene amplicons. During the 60-day study the prokaryotic communities were stable in time but were affected by their position in the system. The first stage of solid waste digestion was operated in an anaerobichydrolytic leach bead reactor with high organic solids content, the microbial communities were dominated by members of the orders Bacteroidales (62%), Selenomonadales (15%), Lactobacillales (13%), Clostridiales (4%) and Rhodospirillales (1%). At this stage, a vertical stratification acted as a transition zone from aerobic to anaerobic environments modifying significantly the composition and structure of bacterial communities. The second stage occurred in an up-flow anaerobic sludge bed reactor specialized in acidogenesismethanogenesis, where the leachate of the first stage was co-fed with municipal wastewater. In this stage, the bacterial community was dominated by members of the orders Pseudomonadales, Clostridiales, Burkholderiales, Bacteroidales and Syntrophobacterales (accounting for 52%), while the most abundant orders of the archaeal community corresponded to Methanosarcinales (72%) and Methanobacteriales (13%), both of them with methanogenic capacity.