Diversity and interactions of microbial functional genes under differing environmental conditions: insights from a membrane bioreactor and an oxidation ditch.

Yu Xia,Man Hu,Xianghua Wen,Xiaohui Wang,Yunfeng Yang,Jizhong Zhou

doi:10.1038/srep18509

Abstract

The effect of environmental conditions on the diversity and interactions of microbial communities has caused tremendous interest in microbial ecology. Here, we found that with identical influents but differing operational parameters (mainly mixed liquor suspended solid (MLSS) concentrations, solid retention time (SRT) and dissolved oxygen (DO) concentrations), two full-scale municipal wastewater treatment systems applying oxidation ditch (OD) and membrane bioreactor (MBR) processes harbored a majority of shared genes (87.2%) but had different overall functional gene structures as revealed by two datasets of 12-day time-series generated by a functional gene array-GeoChip 4.2. Association networks of core carbon, nitrogen and phosphorus cycling genes in each system based on random matrix theory (RMT) showed different topological properties and the MBR nodes showed an indication of higher connectivity. MLSS and DO were shown to be effective in shaping functional gene structures of the systems by statistical analyses. Higher MLSS concentrations resulting in decreased resource availability of the MBR system were thought to promote positive interactions of important functional genes. Together, these findings show the differences of functional potentials of some bioprocesses caused by differing environmental conditions and suggest that higher stress of resource limitation increased positive gene interactions in the MBR system.

Highlights

Environmental heterogeneity, defined as spatial and temporal variation in the physical, chemical and biological environment, is a fundamental property of ecosystems[2]
mixed liquor suspended solid (MLSS) concentration of the OD system was mantained around 4,500 mg/L, and that of the Membrane bioreactors (MBRs) system was around 7,000 mg/L
To clarify the details of the functional potential differentiations of the two systems, we focused on the diversity of three important functional gene categories - carbon cycling, nitrogen cycling and phosphorus utilization, as the removal of carbon, nitrogen and phosphorus pollutants are the main task of municipal wastewater treatment plants (MWTPs)

Summary

Introduction

Environmental heterogeneity, defined as spatial and temporal variation in the physical, chemical and biological environment, is a fundamental property of ecosystems[2]. Numerous studies focus on the relationship between microbial community diversity and environmental conditions mainly based on 16S rRNA genes or specific functional genes. They reveal the differences in microbial diversity and composition resulting from the differentiations of, such as, influent chemical oxygen demand (COD inf) concentrations[3], dissolved oxygen (DO) concentrations[4] and solid retention time (SRT)[5]. Full-scale MBR and CAS systems for municipal wastewater treatment are both meant to support the slow-growing populations like nitrifiers, certain K-strategists may be advantaged in the MBRs with longer SRTs. Different DO concentrations may cause specific differences in the composition of microbial communities. Apart from microbial diversity, the ecological interactions of microbes in MBR systems have never been reported, let alone the interpretation of how possible microbial interactions of ecosystems differ with gradients of substrate availability

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Results

Conclusion