Abstract
Biological treatment of waste water from bulk drug production, contaminated with high levels of fluoroquinolone antibiotics, can lead to massive enrichment of antibiotic resistant bacteria, resistance genes and associated mobile elements, as previously shown. Such strong selection may be boosted by the use of activated sludge (AS) technology, where microbes that are able to thrive on the chemicals within the wastewater are reintroduced at an earlier stage of the process to further enhance degradation of incoming chemicals. The microbial community structure within such a treatment plant is, however, largely unclear. In this study, Illumina-based 16S rRNA amplicon sequencing was applied to investigate the bacterial communities of different stages from an Indian treatment plant operated by Patancheru Environment Technology Limited (PETL) in Hyderabad, India. The plant receives waste water with high levels of fluoroquinolones and applies AS technology. A total of 1,019,400 sequences from samples of different stages of the treatment process were analyzed. In total 202, 303, 732, 652, 947 and 864 operational taxonomic units (OTUs) were obtained at 3% distance cutoff in the equilibrator, aeration tanks 1 and 2, settling tank, secondary sludge and old sludge samples from PETL, respectively. Proteobacteria was the most dominant phyla in all samples with Gammaproteobacteria and Betaproteobacteria being the dominant classes. Alcaligenaceae and Pseudomonadaceae, bacterial families from PETL previously reported to be highly multidrug resistant, were the dominant families in aeration tank samples. Despite regular addition of human sewage (approximately 20%) to uphold microbial activity, the bacterial diversity within aeration tanks from PETL was considerably lower than corresponding samples from seven, regular municipal waste water treatment plants. The strong selection pressure from antibiotics present may be one important factor in structuring the microbial community in PETL, which may affect not only resistance promotion but also general efficiency of the waste treatment process.
Highlights
Waste water from antibiotic production often contains high levels of antibiotics, indicating risks for the promotion of antibiotic resistance inside the treatment plants or in contaminated environments [1]
At 3% cut off, the EQR had the lowest bacterial diversity indicated by the number of operational taxonomic units (OTUs), Chao 1 index and the Shannon diversity index (Table 1)
The rarefaction curves represented in S1 Fig, demonstrate that bacterial OTU richness was lowest in the EQR, and gradually increased along the activated sludge (AS) treatment process
Summary
Waste water from antibiotic production often contains high levels of antibiotics, indicating risks for the promotion of antibiotic resistance inside the treatment plants or in contaminated environments [1]. Studies on penicillin and oxytetracycline production in China indicated an enrichment of antibiotic resistant bacteria and mobile genetic elements during biological treatment of antibiotic-contaminated waste [2, 3]. We have previously studied an industrial waste water treatment plant (WWTP) in Patancheru, India operated by Patancheru Environment Technology Limited (PETL) [4, 5, 6, 7, 8]. Kristiansson et al (2011) demonstrated very high levels of resistance genes to several classes of antibiotics in sediment of the river where PETL used to discharge their effluent. A culture-based study on bacteria thriving inside PETL revealed many highly multidrug resistant bacterial strains, of the genera Pseudomonas and Ochrobactrum [8]
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