Response of sedimentary oxygen consumption and bacterial community composition to temporal re-oxygenation in a seasonally hypoxic enclosed bay. marine sediment metagenome

In a seasonally hypoxic enclosed bay, dissolved oxygen (DO) concentration at the bottom is commonly transiently disturbed by episodic oxygen supply events. We therefore aimed at determining the potential sediment oxygen consumption (SOC) that is induced by artificial replenishment of oxygen, and the relative contribution of biological oxygen consumption (BOC) and chemical oxygen consumption (COC) in the sediment. We also performed amplicon sequencing of the bacterial 16S rDNA for the surface sediment samples (0-5 mm depth) before and after the replenishment of oxygen. COC potentially increased under hypoxic period due to accumulation of reduced compounds such as hydrogen sulfide. Similarly, BOC also potentially increased at the hypoxic condition. Relative abundance of amplicon sequence variants (ASVs) from Woeseia (Woeseiaceae, Gammaproteobacteria) contributed the most to the total ASVs in the sediment layers across the sampling months. No significant shift in the bacterial community composition was observed between normoxic and hypoxic periods. However, the relative abundance of ASVs from potentially sulfur oxidizing Arcobacter (Arcobacteraceae) in one sample drastically increased from <1% at the beginning to nearly 13% after 24 hours of incubation. This coincided with the time when BOC peaked across the sampling periods. These results suggested that (1) both COC and BOC potentially increased during hypoxic period and may contribute to re-establishment of hypoxia, (2) the predominant bacteria in the surface sediment of Omura Bay were made up of a group of bacteria ubiquitous in the marine sediment, and (3) sulfur oxidizing Arcobacter can contribute to an increase in the potential BOC under hypoxic conditions.