Identification of a Thiomicrospira denitrificans -Like Epsilonproteobacterium as a Catalyst for Autotrophic Denitrification in the Central Baltic Sea

Abstract

Identification and functional analysis of key members of bacterial communities in marine and estuarine environments are major challenges for obtaining a mechanistic understanding of biogeochemical processes. In the Baltic Sea basins, as in many other marine environments with anoxic bodies of water, the oxic-anoxic interface is considered a layer of high bacterial turnover of sulfur, nitrogen, and carbon compounds that has a great impact on matter balances in the whole ecosystem. We focused on autotrophic denitrification by oxidation of reduced sulfur compounds as a biogeochemically important process mediating concomitant turnover of sulfur, nitrogen, and carbon. We used a newly developed approach consisting of molecular analyses in stimulation experiments and in situ abundance. The molecular approach was based on single-strand conformational polymorphism (SSCP) analysis of the bacterial community RNA, which allowed identification of potential denitrifiers based on the sequences of enhanced SSCP bands and monitoring of the overall bacterial community during the experiments. Sequences of the SSCP bands of interest were used to design highly specific primers that enabled (i) generation of almost complete 16S rRNA gene sequences using experimental and environmental DNA as templates and (ii) quantification of the bacteria of interest by real-time PCR. By using this approach we identified the bacteria responsible for autotrophic denitrification as a single taxon, an epsilonproteobacterium related to the autotrophic denitrifier Thiomicrospira denitrificans. This finding was confirmed by material balances in the experiments that were consistent with those obtained with continuous cultures of T. denitrificans. The presence and activity of a bacterium that is phylogenetically and physiologically closely related to T. denitrificans could be relevant for the carbon budget of the central Baltic Sea because T. denitrificans exhibits only one-half the efficiency for carbon dioxide fixation per mol of sulfide oxidized and mol of nitrate reduced of Thiobacillus denitrificans hypothesized previously for this function.

Hypoxia and nitrogen processing in the Baltic Sea water column

“…Contrary to this theory and findings from earlier studies (Brettar and Rheinheimer 1991;Brettar et al 2006;Hannig et al 2007), in this study neither anammox nor denitrification potentials were found around the oxic-anoxic interfaces. The only exception was in March, when low levels of anammox could be detected in the redoxclines of the two stations located at the northern, shallower end of Gotland Basin.…”

“…In this study, however, the low levels of anammox potential were found in both oxic (up to 17 mmol O 2 L 21 ) and sulfidic (2.38 H 2 S mmol L 21 ) layers, with the highest rate measured in the presence of sulfide. The potential anammox rates we measured (10)(11)(12)(13)(14)(15)(16)(17) Instead of active N 2 production at the redoxcline, potential was found at the greater, often sulfidic depths, supporting the theory of the chemolithotrophic nature of the process (Brettar et al 2006;Jensen et al 2009). Denitrification was the only process detected both at the Gotland Deep and at the Landsort Deep, and the activity was always located in the deeper layers sampled, well below the dynamic interface.…”

Analysis of bacterial core communities in the central Baltic by comparative RNA–DNA-based fingerprinting provides links to structure–function relationships

“…Heterotrophic plate counts (colony-forming units) showed a maximum at 30-50 m, indicating the sedimentation of a plankton bloom caused by a stormy period 2 days before sampling. More details on the in-situ conditions and the biogeochemical processes associated are found elsewhere (Wulff et al, 2001;Brettar et al, 2006).…”

Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific oceans

“…To date sulfidic events have been reported from the eastern tropical South Pacific, the Arabian Sea and the Benguela upwelling system by only a handful of studies and hence our current understanding of their regulation, initiation and termination is still limited. Possible analogs for oceanic events are permanently sulfidic areas in enclosed basins of the Baltic Sea (Brettar et al, 2006;Brettar and Rheinheimer, 1991;Glaubitz et al, 2009), the Black Sea (Glaubitz et al, 2010;Jørgensen et al, 1991;Sorokin et al, 1995), the Cariaco Basin off Venezuela (Hayes et al, 2006;Taylor et al, 2001;Zhang and Millero, Figure 5. Schematic representation of the dynamics of a sulfidic event occurring in an oxygen minimum zone, e.g.…”