Bacterial communities in different sections of a municipal wastewater treatment plant revealed by 16S rDNA 454 pyrosequencing

Abstract

In this study, we successfully demonstrated that 454 pyrosequencing was a powerful approach for investigating the bacterial communities in the activated sludge, digestion sludge, influent, and effluent samples of a full scale wastewater treatment plant treating saline sewage. For each sample, 18,808 effective sequences were selected and utilized to do the bacterial diversity and abundance analysis. In total, 2,455, 794, 1,667, and 1,932 operational taxonomic units were obtained at 3 % distance cutoff in the activated sludge, digestion sludge, influent, and effluent samples, respectively. The corresponding most dominant classes in the four samples are Alphaproteobacteria, Thermotogae, Deltaproteobacteria, and Gammaproteobacteria. About 67 % sequences in the digestion sludge sample were found to be affiliated with the Thermotogales order. Also, these sequences were assigned into a recently proposed genus Kosmotoga by the Ribosomal Database Project classifier. In the effluent sample, we found high abundance of Mycobacterium and Vibrio, which are genera containing pathogenic bacteria. Moreover, in this study, we proposed a method to differentiate the "gene percentage" and "cell percentage" by using Ribosomal RNA Operon Copy Number Database.

Fig. 1

Sequences quality trimming flow chart

Fig. 2

Rarefaction curves of the four samples at cutoff levels of 3 % (solid lines) and 6 % (dash lines) created by using RDP’s pyrosequencing pipeline. The error bars show 95 % confidence of upper and lower limits

Fig. 3

Relative abundances of different phyla in the four samples (the results were obtained by using BLASTN combined with MEGAN)

Fig. 4

Sequences assignment results at the genus level. All effective sequences in the four samples were assigned into NCBI taxonomies by using BLASTN and MEGAN. Only nodes with over 30 sequences were shown in this figure. Pie charts indicate the relative sequence abundances of the corresponding nodes in the four samples. Red activated sludge, blue digestion sludge, green influent, yellow effluent

Fig. 5

Top 20 genera in each sample showing the comparison of percentages of 16S rRNA gene number and cell number (a activated sludge, b digestion sludge, c effluent, d influent)