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The anaerobic mineralization of buried organic matter through sulfate reduction and methanogenesis was studied in 2-m-long piston cores of organic-rich, silty-clay sediment from two sites in Limfjorden, Denmark. An extended sulfate-methane transition (SMT) zone was found at 1-1.5-m sediment depth, accompanied by peaks in sulfide (4-6 mmol L-1) and high dissolved inorganic carbon (30-50 mmol L-1). Pore-water acetate concentrations were 2-10 µmol L-1. 14C-acetate was oxidized to 14CO2 in the sulfate zone and reduced to 14CH4 at and below the SMT. CO2 reduction was the predominant pathway of methanogenesis below the sulfate zone. Sulfate reduction rates (SRRs) determined by 35S tracer experiments decreased with depth throughout the sulfate zone from > 100 nmol cm-3 d-1 near the sediment surface to < 1 nmol cm-3 d-1 at depth. The depth trend of rates was equally well described by a power law function and a reactive continuum model. Only a small percentage of the total 35S-SRR was due to anaerobic oxidation of methane. In contrast, diffusion-reaction modeling of pore-water sulfate indicated that sulfate reduction was insignificant throughout the sulfate zone and that most of the activity occurred at the SMT. A comparison of the burial flux of organic carbon below the sulfate zone and the returning flux of methane indicated that the diffusion modeling of pore-water sulfate strongly underestimated in situ SRRs, whereas the 35S data may have overestimated the rates at depth. Modeled and measured SRR could be reconciled provided that bioirrigation reached to at least 20-40-cm sediment depth, which appears realistic given the predominant burrowing polychaete fauna. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lauryl ether sulphate (LES), a synthetic detergent, may sometimes contain an allergenic impurity, which has given rise to several outbreaks of contact dermatitis. Such an outbreak occurred in Denmark in 1971. All cases diagnosed were confined to one household, while other cases may have passed unnoticed. [ABSTRACT FROM AUTHOR]