Abundance and diversity of bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants revealed by high-throughput sequencing.

Zhu Wang,Bo Liu,Xin Lu,Chao Long,Aimin Li,Yan Li,Xu-Xiang Zhang,Hemant J Purohit

doi:10.1371/journal.pone.0113603

Abstract

Biological nitrification/denitrification is frequently used to remove nitrogen from tannery wastewater containing high concentrations of ammonia. However, information is limited about the bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants (WWTPs) due to the low-throughput of the previously used methods. In this study, 454 pyrosequencing and Illumina high-throughput sequencing, combined with molecular methods, were used to comprehensively characterize structures and functions of nitrification and denitrification bacterial communities in aerobic and anaerobic sludge of two full-scale tannery WWTPs. Pyrosequencing of 16S rRNA genes showed that Proteobacteria and Synergistetes dominated in the aerobic and anaerobic sludge, respectively. Ammonia-oxidizing bacteria (AOB) amoA gene cloning revealed that Nitrosomonas europaea dominated the ammonia-oxidizing community in the WWTPs. Metagenomic analysis showed that the denitrifiers mainly included the genera of Thauera, Paracoccus, Hyphomicrobium, Comamonas and Azoarcus, which may greatly contribute to the nitrogen removal in the two WWTPs. It is interesting that AOB and ammonia-oxidizing archaea had low abundance although both WWTPs demonstrated high ammonium removal efficiency. Good correlation between the qPCR and metagenomic analysis is observed for the quantification of functional genes amoA, nirK, nirS and nosZ, indicating that the metagenomic approach may be a promising method used to comprehensively investigate the abundance of functional genes of nitrifiers and denitrifiers in the environment.

Highlights

Tannery wastewater is characterized by high contents of nitrogen, organic compounds and salt ions [1, 2], and the complexity of the wastewater components can affect microbial nitrification/denitrification processes that have been frequently used for nitrogen removal in wastewater treatment plants (WWTPs)
Four sludge samples were collected from the two WWTPs, including one anaerobic sludge sample (A-A) from the UASB and one aerobic sludge sample (A-O) from the last aerobic tank of the A/O reactor in WWTPA, and two aerobic sludge samples separately collected from the oxidation ditch (B-D) and the last aerobic tank of the A/O reactor (B-O) in WWTPB
operational taxonomic units (OTUs) and Shannon index analysis based on 16S rRNA gene pyrosequencing showed that the sample A-O from WWTPA had the richest biodiversity, followed by the anaerobic sludge sample A-A from the same WWTP (Table S3)

Summary

Introduction

Tannery wastewater is characterized by high contents of nitrogen, organic compounds and salt ions [1, 2], and the complexity of the wastewater components can affect microbial nitrification/denitrification processes that have been frequently used for nitrogen removal in wastewater treatment plants (WWTPs). QPCR and metagenomic analysis consistently revealed that the relative abundance of bacterial amoA gene was higher in sample A-O than in the other sludge samples (Figure 4B and D).

Results

Conclusion