ABSTRACT. The diversity of microbiota in waste waters has not been thoroughly examined, despite the potential impact of microbes on effluent quality. Wastewater microbial communities harbor pathogenic bacteria, viruses, and parasites. To study microbial communities in domestic sewage outfalls, 454 pyrosequencing technology was used to investigate the composition of microbial communities associated with municipal wastewater during different seasons sampled over the course of one year. A total of 195,103 16S rRNA gene sequences were obtained from 20 samples. The R software was used to calculate the number of indices describing the alpha diversity associated with each bacterial assemblage. In this study, the a-diversity index (Hꞌ, D, J), in which higher numbers represent more diversity, was found to change with seasonal cycle. The diversity of bacterial assemblages was high Microbial communities in sewage outfalls in all samples, indicating that species diversity was also very high. The taxonomic composition of the assemblages varied considerably among samples, with some dominated by Proteobacteria, while others were dominated by Bacteroidetes or Firmicutes. In 2 samples, the relative prevalence of Proteobacteria exceeded 90%. α-Proteobacteria, b-proteobacteria, and g-proteobacteria represented 90% or more of all Proteobacteria. The present characterization of wastewater from five sewage outfalls indicated the presence of some pathogenic bacteria. The g-Proteobacteria in sewage wastefalls identified in this study included Enterobacteriaceae, Vibrionaceae, Pseudomonadaceae, Salmonella, Yersinia, Vibrio, and Pseudomonas aeruginosa.