*2.7. Microbial Community Analysis*

Total DNA was extracted from the sludge at the end of the readdition experiments using a PowerSoil DNA Isolation kit (QIAGEN, Venlo, Netherlands). The purified DNA was used as a template for the amplification of the 16S rRNA gene sequence containing the V5-V8 variable regions using a 5 -primer containing an Illumina adaptor and a 16S rRNA gene-specific sequence (5 -CCTACGGGNBGCASCAG-3 ). The sequence of the 3 -primer contained an Illumina adaptor and a 16S rRNA gene-specific sequence (5 -GACTACNVGGGTATCTAATCC-3 ). PCR was performed as previously described [30,31]. Next generation sequencing (NGS) was performed at the Genome Center of National Yang-Ming University, Taiwan, using the MiSeq platform (Illumina, Inc, San Diego, CA, USA.). A chimera check was used to analyze the 16S rRNA gene sequences to remove chimeras. The remaining sequences were subsequently analyzed using the classifier software of the Ribosomal Database Project (http://pyro.cme.msu.edu/) for phylogenetic assignment. Similarity (95%) was used for bacterial grouping. Xenobiotic biodegradation-associated bacteria were identified using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database [32]. A cluster analysis of the bacterial community compositions was performed using the Heatmap function in the ComplexHeatmap package of R (www.r-project.org).
