Potential oxygen consumption and community composition of sediment bacteria in a seasonally hypoxic enclosed bay

Abstract

The dynamics of potential oxygen consumption at the sediment surface in a seasonally hypoxic bay were monitored monthly by applying a tetrazolium dye (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride [INT]) reduction assay to intact sediment core samples for two consecutive years (2012–2013). Based on the empirically determined correlation between INT reduction (INT-formazan formation) and actual oxygen consumption of sediment samples, we inferred the relative contribution of biological and non-biological (chemical) processes to the potential whole oxygen consumption in the collected sediment samples. It was demonstrated that both potentials consistently increased and reached a maximum during summer hypoxia in each year. For samples collected in 2012, amplicon sequence variants (ASVs) of the bacterial 16S rRNA genes derived from the sediment surface revealed a sharp increase in the relative abundance of sulfate reducing bacteria toward hypoxia. In addition, a notable shift in other bacterial compositions was observed before and after the INT assay incubation. It was Arcobacter (Arcobacteraceae, Campylobacteria), a putative sulfur-oxidizing bacterial genus, that increased markedly during the assay period in the summer samples. These findings have implications not only for members of Delta- and Gammaproteobacteria that are consistently responsible for the consumption of dissolved oxygen (DO) year-round in the sediment, but also for those that might grow rapidly in response to episodic DO supply on the sediment surface during midst of seasonal hypoxia.

Hidden aliens: Application of digital PCR to track an exotic foraminifer across the Skagerrak (North Sea) correlates well with traditional morphospecies analysis

“…T1 constituted the largest proportion of the foraminiferal community was the comparatively hospitable Hake fjord with well‐oxygenated bottoms, also demonstrating a capacity of the species to prosper under benign conditions. The oxygen‐rich sediments of the Hake fjord contained extremely little total DNA, which is likely caused, in part, by the presence of abundant dissolved oxygen causing the breakdown of DNA from dead organisms (Corinaldesi et al, 2008, 2011) or by lower bacterial abundances (Mori et al, 2021).…”

“…Neither oxygen respiration nor denitrification by foraminifera is viable here, since nitrification and therefore availability of nitrate is also limited due to lack of oxygen. Despite this, the By fjord has remarkably high total concentrations of sediment‐extracted DNA, likely due to (1) the anoxic conditions preserving DNA of dead organisms in the sediment (Corinaldesi et al, 2011) and (2) presence of abundant bacteria in anoxic sediments (Mori et al, 2021).…”

Spatio-temporal variation of bacterial community structure in two intertidal sediment types of Jiaozhou Bay

“…Campilobacterota has been observed at higher abundances (>5%) in thermogenic hydrocarbon seep sediments (Li et al, 2023) and is involved in mediating oxidation of sulfur, sulfide or sulphate in intertidal sediments (7.90-22.15%) (Carrier et al, 2020;Fang et al, 2022). The genus Arcobacter has been found to increase in abundance in anoxic surface sediments, and in addition, is highly responsive to oxygenation events (Broman et al, 2017;Mori et al, 2021). Therefore, it is likely that hydrocarbon, sulfide and oxygen (low summer oxygen, low mud permeability and low circulation rates within the bay) are responsible for the increased abundance of Campilobacterota in summer mud samples at LC.…”