Sulfate‐reducing bacteria in marine sediment (Aarhus Bay, Denmark): abundance and diversity related to geochemical zonation

Abstract

In order to better understand the main factors that influence the distribution of sulfate-reducing bacteria (SRB), their population size and their metabolic activity in high- and low-sulfate zones, we studied the SRB diversity in 3- to 5-m-deep sediment cores, which comprised the entire sulfate reduction zone and the upper methanogenic zone. By combining EMA (ethidium monoazide that can only enter damaged/dead cells and may also bind to free DNA) treatment with real-time PCR, we determined the distributions of total intact bacteria (16S rDNA genes) and intact SRB (dsrAB gene), their relative population sizes, and the proportion of dead cells or free DNA with depth. The abundance of SRB corresponded in average to 13% of the total bacterial community in the sulfate zone, 22% in the sulfate-methane transition zone and 8% in the methane zone. Compared with the total bacterial community, there were relatively less dead/damaged cells and free DNA present than among the SRB and this fraction did not change systematically with depth. By DGGE analysis, based on the amplification of the dsrA gene (400 bp), we found that the richness of SRB did not change with depth through the geochemical zones; but the clustering was related to the chemical zonation. A full-length clone library of the dsrAB gene (1900 bp) was constructed from four different depths (20, 110, 280 and 500 cm), and showed that the dsrAB genes in the near-surface sediment (20 cm) was mainly composed of sequences close to the Desulfobacteraceae, including marine complete and incomplete oxidizers such as Desulfosarcina, Desulfobacterium and Desulfococcus. The three other libraries were predominantly composed of Gram-positive SRB.

Global rates of marine sulfate reduction and implications for sub–sea-floor metabolic activities

“…2C) and cell specific rates ( . Simultaneous measurements of SRRs and sulfate reducing microorganism abundances are rare but the existing data are consistent with our model (22)(23)(24)(25)(26). The majority of these data exist for relatively shallowwater, high-productivity sites (e.g., Aarhus Bay), with surficial cellspecific SRRs around 0.…”

What Do We Really Know about the Role of Microorganisms in Iron Sulfide Mineral Formation?

“…The interactions between extracellular sulfide mineral precipitates and microorganisms are thus of great interest to understand the pathways of organic matter preservation in modern and ancient systems. For example, studies of marine sediments in Aarhus Bay in Denmark found that the highest sulfide production rates are attributed to members of the Desulfobacteraceae and that Fe 3 S 4 is most abundant in the sediment just below these communities (Leloup et al, 2009;Holmkvist et al, 2011). Although the focus of this mini review is on extracellular iron sulfide minerals, it should be noted that some magnetotactic bacteria (MTB) form intracellular iron sulfides ranging in size 35-120 nm, that are contained in bilayer membranes within an organelle called the magnetosome (Lefevre and Bazylinski, 2013).…”

Off Limits: Sulfate below the Sulfate-Methane Transition

“…If the argument that sulfur isotope fractionation by sulfate reduction is negligible in the deep sulfate zone holds, the oxygen isotope effects should be negligible as well, because both processes are linked by the reversibility of the sulfate reduction pathway (Brunner et al, 2005(Brunner et al, , 2012. Alternatively, sulfate consuming organisms in the methanic zone may employ sulfate reduction pathways that do not fractionate sulfur isotopes, for example pathways that are similar to sulfate assimilation or yet to-be elucidated sulfate reduction pathways inferred for ANME (Milucka et al, 2012), however, it needs to be noted that the phylogenetic diversity of sulfate reducers in the methanic zone are rather similar to those in the lower part of the sulfate zone (Leloup et al, 2009). …”

“…Another example for the potential of cryptic sulfur cycling comes from a sub-glacial lake in Antarctica (Mikucki et al, 2009), where sulfate-sulfur is apparently reduced and re-oxidized back to sulfate via coupling to reductive iron cycling. The finding of sulfate reducing microorganisms in in subsurface methanic sediments from Aarhus Bay (Baltic Sea) and Black Sea sediments (Leloup et al, 2007(Leloup et al, , 2009) that were traditionally considered to be sulfate-free and devoid of active sulfate reduction, and the presence of low, but detectable sulfate in subsurface methanic sediments from Aarhus Bay (Holmkvist et al, 2011) implies that cryptic sulfur cycling is an ongoing process throughout the anoxic sediment column.…”