Community Composition and Carbon Utilization Profiles of Yodo River Microbes in Brackish and Freshwater Sediments

Abstract

This study was undertaken to obtain basic data related to the community composition and metabolic functions of estuarine microbes. Water and sediment samples were collected in 2014－2015 from Juso Lagoon (brackish area) and Shirokita Wando (freshwater area) along the Yodo River flowing to Osaka Bay. The genotypes and phenotypes of the estuarine microbes were evaluated, respectively, using eubacterial 16S rRNA genes based on terminal-restriction fragment length polymorphism (T-RFLP) and on carbon-utilization tests using Biolog GN2 plates containing 95 separate carbon sources. The microbial community structure and carbon utilization profiles of the brackish sediment differed greatly from those of freshwater sediment. Canonical correlation analysis revealed that the estuarine microbes could be characterized by conductivity (salinity) and temperature of their habitats. Deltaproteobacteria including sulfate-reducing bacteria were possibly dominant in the brackish sediment, suggesting effects of the high sulfate concentration in seawater on the microbial community. The heterotrophic population and the diversity index calculated from the T-RFLP analysis and the carbon source utilization tests in summer and autumn in vegetation zones were higher than those in non-vegetation zones of both brackish and freshwater areas, suggesting that river vegetation can stimulate microbial activity in the rhizosphere.