Paper Title
A Study on Effects of 1,3-Butadiene Exposure on Bacterial Community in Activated Sludge Using Next-Generation Sequencing

Abstract
This study investigated effects of 1,3-butadiene (1,3-BD) exposure on bacterial community in activated sludge samples (designated as SL2 and SL4) collected from 2 different wastewater treatment facilities of petrochemical industry. While SL2 represented a bacterial community with no prior exposure to 1,3-BD and/or toluene, SL4 represented a bacterial community with prior exposure to both compounds. The sludge samples were enriched with 100 ppm of 1,3-BD (contributing 8,600 ppm of toluene as a solvent) for 6 weeks. The sludge samples exposed with only toluene were also conducted in parallel. Changes in microbial community profile was monitored based on 16s rDNA using next-generation sequencing platform. The sequences were assigned to the phylum as well as lower levels to represent the relative microbial abundance in each sample. Before an enrichment (Week 0), Proteobacteria (Alpha- and Beta-proteobacteria), Planctomycetes and Chloroflexi were the dominant bacterial populations in both samples whereas Firmicutes was found only in SL2. After an enrichment with toluene, Planctomycetes, Chloroflexi and Chlorobi tended to decrease over time while Actinobacteria and Candidatus Saccharibacteria (Candidate division TM7) increased continuously. In SL2, Firmicutes (Bacilli) was found to be the dominated taxa during toluene exposure while Proteobacteria (Alpha- and Beta-proteobacteria) decreased over time. In case of 1,3-BD exposure, Proteobacteria increased in both samples. Taxonomic classification into class level indicated that Alapha-proteobacteria (mainly Rhizobiales) and Beta-proteobacteria (mainly Burkholderiales) were the most abundant classes in both samples while a significant increase in Gamma-proteobacteria (Xanthomonadales and Pseudomonadales) was mainly observed in SL4. The fact that Beta-proteobacteria (mainly Burkholderiales) was the highest dominated bacterial populations in both samples exposed with 1,3-BD suggested that Burkholderiales may involve with degradation of 1,3-BD or its metabolites. An understanding on the bacterial community in toxic waste as well as how they evolve after an exposure can be applied further for selection of remediation solutions and environmental management. Keywords- 1,3-Butadiene, Activated sludge, Bacterial community, Next-generation sequencing