New research published in Engineering outlines consistent ecological rules governing microbial community assembly across man-made biotreatment systems, addressing longstanding gaps in understanding how high-intensity environmental perturbations shape microbial dynamics and reactor operational performance. Led by researchers from Tianjin University alongside collaborators from the Chinese Academy of Sciences and Georgia Institute of Technology, the work draws on meta-analysis of nine independent amplicon sequencing datasets collected from bioreactors running under diverse operational conditions, applying null model frameworks to quantify the relative contributions of stochastic and deterministic assembly processes through the β-nearest taxon index (βNTI) and Bray–Curtis-based Raup–Crick metric (RCbray).

Prior microbial ecology research has clarified assembly patterns in natural ecosystems such as soils and groundwater, yet few systematic analyses have captured succession trajectories within engineered micro-ecosystems frequently exposed to repeated shocks, substrate shifts and operational stressors. The team’s null model classification sets clear thresholds for distinguishing assembly drivers: βNTI values greater than 2 signal variable selection as the dominant force, values below −2 point to homogeneous selection, and |βNTI| < 2 marks stochastic assembly dominated by ecological drift, homogenizing dispersal and dispersal limitation. Data from two long-term full-scale activated sludge facilities with stable influent conditions demonstrated that stochastic processes prevail during steady operation, accompanied by sustained contaminant removal efficiency close to maximum levels, with homogenizing dispersal creating consistent community composition and stable functional output over multi-month monitoring periods.

For bioreactors undergoing single environmental disturbances, including initial sludge acclimation, biofilm carrier colonization and nitrite stress exposure, deterministic processes dominated the startup and adaptive phases before gradually receding as operation stabilized. Introduction of external stressors such as elevated chemical oxygen demand loading, acute ammonia shock and xenobiotic 3-chloroaniline addition amplified the weight of deterministic assembly pathways, triggering heterogeneous selection as microbial strains with divergent tolerance thresholds responded unevenly to modified environmental filters. Multiple sequential disturbances triggered repeated oscillations between deterministic and stochastic dominance, with each perturbation event elevating selection pressure and reshaping community β-diversity trajectories as visualized via nonmetric multidimensional scaling.

Linear regression analysis identified a consistent inverse correlation between absolute βNTI values and reactor contaminant removal efficiency at statistically significant levels, confirming that low treatment performance aligns with deterministic assembly regimes, while sustained functional stability coincides with stochastic community dynamics regardless of reactor configuration, including sequencing batch reactors, moving bed biofilm reactors, gas biofilters and continuous stirred tank reactors. The research further disentangled five core assembly processes within bioreactor environments, verifying that dispersal-related stochastic mechanisms carry greater overall relative importance than homogeneous or heterogeneous selection under undisturbed running states, while disturbance events significantly raise the proportional influence of deterministic selection filters.

The authors integrated cross-dataset observations into a three-phase conceptual model separating community succession into initial, adaptive and restored stages, grouping bioreactor operations into four categories defined by the frequency and persistence of environmental disturbances. Beyond advancing theoretical microbial ecology for engineered ecosystems, the findings deliver actionable reference for bioreactor regulation, highlighting that inoculation with functionally mature activated sludge can shorten startup acclimation phases, while deliberate adjustments to substrate loading and operational parameters must balance functional enhancement against risks of destabilizing microbial community equilibrium. All raw sequencing datasets supporting the analysis are deposited in NCBI GenBank public repositories for further cross-verification and extended research into engineered microbial ecosystem resilience.

The paper “Rules Governing General Assembly of Microbial Communities in Engineered Biotreatment Processes,” is authored by Yong-Chao Wang, Ya-Hui Lv, Ye Deng, Yu-Ting Lin, Guan-Yu Jiang, John C. Crittenden, Can Wang. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.06.041. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.