Dynamics of Sulfate-Reducing Bacteria Community Structure in Surface Sediment of a Seasonally Hypoxic Enclosed Bay

Abstract

We herein report on the dynamics of a sulfate-reducing bacteria (SRB) community structure in the surface sediment of a seasonally hypoxic enclosed bay for two consecutive years (2012 and 2013). The uppermost (0–5 mm) and subsurface (5–10 mm) layers of sediment were examined with a terminal-restriction fragment length polymorphism (T-RFLP) analysis based on the dissimilatory sulfite reductase (dsrA) gene. The SRB community significantly differed between the two sediment layers over the sampling period. This difference was mainly attributed to operational taxonomic units (OTUs) that were unique to either of the sediment layers. However, nearly 70% of total OTUs were shared between the two layers, with a few predominating. Therefore, no significant shift was observed in the SRB community structure under varying dissolved oxygen (DO) conditions in bottom water overlying the sediment surface. An additional analysis of 16S rRNA gene amplicon sequences, conducted for three uppermost sediment samples (July, August, and September in 2012), revealed that Desulfococcus, a member of SRB with high tolerance to oxygen, was the predominant Deltaproteobacteria across the uppermost sediment samples. Based on the predominance of shared OTUs across the SRB community in the sediment (0–10 mm) regardless of bottom-water DO, some SRB that are physiologically tolerant of a wide range of DO conditions may have dominated and masked changes in responsive SRB to DO concentrations. These results suggest that the SRB community structure in the enclosed bay became stable under repeated cycles of seasonal hypoxia, but may be compromised if the severity of hypoxia increases in the future.

Potential Oxygen Consumption and Community Composition of Sediment Bacteria in a Seasonally Hypoxic Enclosed Bay

“…Furthermore, members of chemolithotrophic cable bacteria have also been shown to make a large contribution to the total annual oxygen uptake in seasonally sul dic sediment [12]. In our previous studies of Omura Bay, we found a shift in sediment bacterial community structure that occurred as DO levels in the bottom water changed [14,15]. Members of the aerobic Gammaproteobacterial group decreased as oxygen became depleted, while members of the sulfate-reducing Deltaproteobacterial group increased and became predominant.…”

“…According to our previous study [14,15], temporal shifts in the BCC in the surface sediment of Omura Bay were characterized by decreases in the relative abundance of the ASVs a liated with Gammaproteobacteria toward less oxic conditions; conversely, those a liated with Deltaproteobacteria exhibited the opposite results. The present results were essentially consistent with this trend, although there was a peak in the relative abundance of Deltaproteobacteria under the oxic condition in September 2012 (Table 1).…”

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

“…According to our previous study (Mori et al, 2018a;Mori et al, 2018b), temporal shifts in the bacterial community in the surface sediment of Omura Bay were characterized by decreases in the relative abundance of the ASVs affiliated with Gammaproteobacteria toward less oxic conditions; conversely, those affiliated with Deltaproteobacteria exhibited the opposite results. The present results were essentially consistent with this trend, although there was a peak in the relative abundance of Deltaproteobacteria under the oxic condition in September 2012 (Fig.…”

“…Furthermore, members of chemolithotrophic cable bacteria have also been shown to make a large contribution to the total annual oxygen uptake in seasonally sulfidic sediment ( Seitaj et al, 2017 ). In our previous studies of Omura Bay, we found a shift in sediment bacterial community structure that occurred as DO levels in the bottom water changed ( Mori et al, 2018a ; Mori et al, 2018b ). Members of the aerobic Gammaproteobacterial group decreased as oxygen became depleted, while members of the sulfate-reducing Deltaproteobacterial group increased and became predominant.…”

Impact of seasonal hypoxia on benthic copepod communities in Omura Bay, a highly enclosed coastal sea in southwestern Japan

“…Furthermore, shifts in bacterial communities were also evident in response to the availability of dissolved oxygen (DO). While the relative abundance of Gammaproteobacteria was found to correlate positively with DO, the abundance of Deltaproteobacteria was inversely correlated with DO (Mori et al 2018, Mori & Wada 2019. These results strongly suggest that DO availability on the sea bottom plays a fundamental role in shaping the bacterial community in sediment surfaces in the area.…”