Increasing the availability of oxygen promotes the metabolic activities and population growth of cable bacteria in freshwater sediments

Abstract

Cable bacteria have been discovered in various marine and freshwater habitats, and their unique metabolism named electrogenic sulfide oxidation (e-SOx) is of great ecological significance to aquatic ecosystems. However, the environmental factors that determining the dynamics and abundance of cable bacteria in freshwater sediments are not well understood. In this study, we examined the activity and growth of cable bacteria in response to the change of oxygen availability in freshwater sediments. The metabolic activity of cable bacteria was quantified by microsensor profiling, while their abundance was determined by fluorescence in situ hybridization and 16S rRNA gene sequencing. The increase of oxygen availability greatly promoted the metabolic activity and proliferation of cable bacteria, as reflected by a higher rate of e-SOx and a larger population size. As affected by the change of sulfide availability and oxygen demand with the proliferation of cable bacteria, these promoting effects were more pronounced at later development stage. Moreover, the elevation of oxygen availability drove the downwards growth of cable bacteria and the increased inventories of dissolved sulfate in deeper sediment layers, which may expand the influences of cable bacteria on sediment biogeochemical cycling on the vertical scale. Our results contribute to further understanding of the correlations between oxygen availability and growth dynamics of cable bacteria in natural environments.