The Microbiota and Abundance of the Class 1 Integron-Integrase Gene in Tropical Sewage Treatment Plant Influent and Activated Sludge.

Magna C Paiva,Mariana P Reis,Patrícia S Costa,Andréa M A Nascimento,Regina M D Nardi,Marcelo P Ávila,Ramy K Aziz

doi:10.1371/journal.pone.0131532

Magna C Paiva, Mariana P Reis + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0131532

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Abstract

Bacteria are assumed to efficiently remove organic pollutants from sewage in sewage treatment plants, where antibiotic-resistance genes can move between species via mobile genetic elements known as integrons. Nevertheless, few studies have addressed bacterial diversity and class 1 integron abundance in tropical sewage. Here, we describe the extant microbiota, using V6 tag sequencing, and quantify the class 1 integron-integrase gene (intI1) in raw sewage (RS) and activated sludge (AS). The analysis of 1,174,486 quality-filtered reads obtained from RS and AS samples revealed complex and distinct bacterial diversity in these samples. The RS sample, with 3,074 operational taxonomic units, exhibited the highest alpha-diversity indices. Among the 25 phyla, Proteobacteria, Bacteroidetes and Firmicutes represented 85% (AS) and 92% (RS) of all reads. Increased relative abundance of Micrococcales, Myxococcales, and Sphingobacteriales and reduced pathogen abundance were noted in AS. At the genus level, differences were observed for the dominant genera Simplicispira and Diaphorobacter (AS) as well as for Enhydrobacter (RS). The activated sludge process decreased (55%) the amount of bacteria harboring the intI1 gene in the RS sample. Altogether, our results emphasize the importance of biological treatment for diminishing pathogenic bacteria and those bearing the intI1 gene that arrive at a sewage treatment plant.

Highlights

Water is fundamental to life on earth and is considered a renewable and infinite resource, it is still limited
As outlined in a review by Gillings et al [4], class 1 integron-integrase is consistently linked to genes that confer resistance to antibiotics, disinfectants and heavy metals, is found in pathogenic and commensal bacterial species of humans and animals and is able to move between species
To gain insight into this knowledge gap, we investigated the bacterial diversity of raw sewage (RS) and AS of a full-scale activated sludge system using high-throughput sequencing

Summary

Introduction

Water is fundamental to life on earth and is considered a renewable and infinite resource, it is still limited. Many studies based on 16S rRNA gene analysis have described microbial groups found in anaerobic reactors and AS [11,12,13], but less is known regarding microbiota from raw sewage (RS) and the abundance of the class 1 integron-integrase gene (intI1) in this environment.

Results

Conclusion