Temporal Diversity And Assembly Patterns Of Microbial Communities In Municipal Wastewater Treatment Systems

The wastewater treatment plant(WWTP)is an indispensable unit of modern cities,which is important for the access to safe water and the sustainable development of cities.Biological treatment process is the most widely used technique in municipal wastewater treatment,in which microbial communities play key roles in pollutant removal.Thus,understanding diversity and composition of microbial communities in WWTPs is key to the understanding of the biological wastewater treatment processes.Also,clarification of microbial dynamics can benefit the understanding and prediction of treatment efficiencies and stabilities of WWTPs.However,comprehensive insights on these topics have not been achieved yet.Therefore,in this study,high-throughput methods including 16 S rRNA gene-based Illumina Miseq sequencing and a comprehensive functional microarrayGeoChip,integrated with statistical analyses,mathematic modeling and network analysis,were applied,to clarify the diversity and dynamics of microbial communities in full-scale municipal wastewater treatment systems with typical treatment processes,which may provide effective suggestions for the design and operation of WWTPs.GeoChip and Illumina sequencing were jointly used in the investigation on microbial diversity of full-scale conventional activated sludge systems and a memberane bioreactor(MBR).High functional gene diversity and taxonomic diversity of activated sludge microbial communities were revealed.All categories of functional genes covered by GeoChip were detected,for example,carbon-,nitrogen-and phosphorus cycling genes and organic remediation genes.High microbial similarity was observed within the conventional activated sludge systems located in the same city.Differences of the abundances of certain sub-categories of carbon-,nitrogen-and phosphorus cycling genes within them were dectected as well.High similarity in microbial composition of the two parallelly-operated MBR and oxidation ditch(OD)systems which treated identical wastewater and had identical inoculum sludge was detected,while some K-strategists that are capable of efficiently utilizing scarce resources were enriched in the MBR.The dynamics patterns the microbial communities in the above mentioned two parallelly-operated MBR and OD systems during 12 consecutive days and 12 consecutive weeks were comprehensively analyzed.Also,the factors shaping community structures were elaborated.Daily and weekly changes in microbial structure of each system wereobserved.Overall functional genes of communities exhibited bigger daily changing rates(12.8 ± 4.6%)than weekly changing rates(5.3 ± 3.6%).The structure of 16 S rRNA genes changed more dramatically(30.5 ±22.7%)than that of functional genes(5.3 ± 3.6%).In response to the relatively big variations in influent characteristics,the weekly changing rates of the16 S rRNA gene structures of the MBR and OD systems increased to 89.7%and 74.7%,respectively.Each system harbored a core community which was highly abundant in both of the 12-day and 12-week datasets.The relative abundances of core functional genes were 58.3–73.5% for the two systems,and those of core operational taxonomic units(OTUs)were 52.8% in the MBR system and 47.7% in the OD system.For the first time,it is showed that the structures of core OTUs in activated sludge were significantly correlated to the removal efficiencies of nitrogen and phosphorus pollutants in the systems,while such a pattern was not observed within overall OTUs or rare OTUs.In the deterministic factors shaping community structures,concentrations of mixed liquor suspended solid(MLSS)and dissolved oxygen(DO)played a major role in shaping community structures during the 12-day sampling,while concentrations of pollutants in influent and temperature played a major role during the 12-week sampling.Stochastic factors played an important role in shaping community structures during the periods of12-day and 12-week sampling.By network analysis,interactions of core genes associated with carbon-,nitrogenand phosphorus cycling in the 12-day dataset and core OTUs in the 12-week dataset of the MBR and OD systems were revealed,respectively.Such analyses have never been reported in earlier studies.It is showed that the MBR community was more tightly linked to each other through more connectivities than the OD community.However,the percentage of negative connectivities(competition and so on)of the MBR community increased during the 12-week sampling,which possibly resulted from the higher stress of substrate scarcity during the 12-week sampling than that of the 12-day sampling.