Abstract
Microbial community assembly in engineered biological systems is often simultaneously influenced by stochastic and deterministic processes, and the nexus of these two mechanisms remains to be further investigated. Here, three lab-scale activated sludge reactors were seeded with identical inoculum and operated in parallel under eight different sludge retention time (SRT) by sequentially reducing the SRT from 15 days to 1 day. Using 16S rRNA gene amplicon sequencing data, the microbial populations at the start-up (15-day SRT) and SRT-driven (≤10-day SRT) phases were observed to be noticeably different. Clustering results demonstrated ecological succession at the start-up phase with no consistent successional steps among the three reactors, suggesting that stochastic processes played an important role in the community assembly during primary succession. At the SRT-driven phase, the three reactors shared 31 core operational taxonomic units (OTUs). Putative primary acetate utilizers and secondary metabolizers were proposed based on K-means clustering, network and synchrony analysis. The shared core populations accounted for 65% of the total abundance, indicating that the microbial communities at the SRT-driven phase were shaped predominantly by deterministic processes. Sloan’s Neutral model and a null model analysis were performed to disentangle and quantify the relative influence of stochastic and deterministic processes on community assembly. The increased estimated migration rate in the neutral community model and the higher percentage of stochasticity in the null model implied that stochastic community assembly was intensified by strong deterministic factors. This was confirmed by the significantly different α- and β-diversity indices at SRTs shorter than 2 days and the observation that over half of the core OTUs were unshared or unsynchronized. Overall, this study provided quantitative insights into the nexus of stochastic and deterministic processes on microbial community assembly in a biological process.
Highlights
Microbial community is shaped by stochastic and deterministic processes (Ofiteru et al, 2010), but the extent to which these two processes influence community development is still a much debated topic (Ayarza and Erijman, 2011; Valentín-Vargas et al, 2012; Zhou et al, 2013)
Stochastic and deterministic processes are identified as two major mechanisms shaping community structure (Ofiteru et al, 2010), but it remains unclear to what extent stochastic and deterministic processes interact with each other and contribute to the selection
The present study addressed this question by characterizing the microbial communities in three lab-scale activated sludge reactors under a strong deterministic factor (i.e., sludge retention time (SRT))
Summary
Microbial community is shaped by stochastic and deterministic processes (Ofiteru et al, 2010), but the extent to which these two processes influence community development is still a much debated topic (Ayarza and Erijman, 2011; Valentín-Vargas et al, 2012; Zhou et al, 2013). Previous studies have focused on the effects of stochastic processes during microbial succession in natural ecosystems including soil (Ferrenberg et al, 2013), groundwater (Zhou et al, 2014), and salt marsh soil (Dini-Andreote et al, 2015). The hypothesis is supported by the findings from natural ecosystems that deterministic disturbance may promote random community assembly (Didham et al, 2005). Strong disturbances such as wildfire can reset assembly processes by exerting adverse impacts on all members in a microbial community, creating a pristine environment in which stochastic processes briefly govern community assembly (Ferrenberg et al, 2013)
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