Investigation of Microbial Flora of Surface Water of Hirano River during Combined Sewer Overflow Discharge

Abstract

Combined sewer overflow (CSO) causes water pollution in the Hirano River in Osaka Prefecture. In this study, we surveyed the microbial flora of the river water surface during CSO discharge. Prokaryote 16S rRNA genes in water samples collected around the Hirano Ichimachi Drainage Station in August and September 2023 were analyzed by next-generation sequencing and correlated with water quality by canonical correlation analysis. Species of Flavobacterium, Acinetobacter, Limnohabitans, Flectobacillus, and Cloacibacterium as well as strictly aerobic Leadbetterella, Rheinheimera, and Vogesella, were observed to be predominant in the samples with less CSO influence. However, in the samples with high suspended solids and chemical oxygen demand concentrations during CSO discharge, anaerobic species of Arcobacter, Bacteroides, Tolumonas, Acidovorax, and Prevotella were observed to be predominant and an increase in the ratio of bacterial genera belonging to the phylum Firmicutes (e.g., Streptococcus, Faecalibacterium, and Ruminococcus) was also observed.