Impact of Different In Vitro Electron Donor/Acceptor Conditions on Potential Chemolithoautotrophic Communities from Marine Pelagic Redoxclines

Abstract

Anaerobic or microaerophilic chemolithoautotrophic bacteria have been considered to be responsible for CO 2 dark fixation in different pelagic redoxclines worldwide, but their involvement in redox processes is still not fully resolved. We investigated the impact of 17 different electron donor/acceptor combinations in water of pelagic redoxclines from the central Baltic Sea on the stimulation of bacterial CO 2 dark fixation as well as on the development of chemolithoautotrophic populations. In situ, the highest CO 2 dark fixation rates, ranging from 0.7 to 1.4 mol liter ؊1 day ؊1 , were measured directly below the redoxcline. In enrichment experiments, chemolithoautotrophic CO 2 dark fixation was maximally stimulated by the addition of thiosulfate, reaching values of up to 9.7 mol liter ؊1 CO 2 day ؊1 . Chemolithoautotrophic nitrate reduction proved to be an important process, with rates of up to 33.5 mol liter ؊1 NO 3 ؊ day ؊1 . Reduction of Fe(III) or Mn(IV) was not detected; nevertheless, the presence of these potential electron acceptors influenced the development of stimulated microbial assemblages. Potential chemolithoautotrophic bacteria in the enrichment experiments were displayed on 16S ribosomal complementary DNA single-strand-conformation polymorphism fingerprints and identified by sequencing of excised bands. Sequences were closely related to chemolithoautotrophic Thiomicrospira psychrophila and Maorithyas hadalis gill symbiont (both Gammaproteobacteria) and to an uncultured nitrate-reducing Helicobacteraceae bacterium (Epsilonproteobacteria). Our data indicate that this Helicobacteraceae bacterium could be of general importance or even a key organism for autotrophic nitrate reduction in pelagic redoxclines.Chemolithoautotrophic bacteria play an important role in biogeochemical cycles of aquatic habitats. Molecular hydrogen and reduced nitrogen (NH 4 ϩ and NO 2 Ϫ ), sulfur (e.g., H 2 S and S 2 O 3 2Ϫ ), metals (e.g., Fe 2ϩ and Mn 2ϩ ) and carbon (e.g., CO and CH 4 ) compounds serve as electron donors for these bacteria (37), whereas oxygen and nitrate mostly serve as electron acceptors. CO 2 dark fixation has been determined in different pelagic redoxclines worldwide. For example, Taylor et al. (42) showed that bacterial chemoautotrophy, fueled by reduced sulfur species, supported an active secondary microbial food web in the redox transition zone of the Cariaco Basin. Depending on the season, dissolved inorganic carbon assimilation (27 to 159 mmol C m Ϫ2 day Ϫ1 ) in this zone was equivalent to 10% to 333% of phytoplankton primary production. Madrid et al. (24) hypothesized that sulfide-oxidizing epsilon symbiont relative clones were responsible for the dark CO 2 fixation. Nitrate, manganese, and iron as potential electron acceptors were available for the epsilon symbiont relatives, but their reduction was not investigated. Jannasch et al. (17) isolated nine chemolithoautotrophic bacterial strains from the anoxic interface of the Black Sea. These isolates were unable to utilize nitrate, manganese,...

High abundance and dark CO2 fixation of chemolithoautotrophic prokaryotes in anoxic waters of the Baltic Sea

“…Potential candidates could belong to the Epsilonproteobacteria, since their appearance around the redoxcline coincides with that of cluster HNA-hs (Labrenz et al 2007). In the Cariaco Basin, Lin et al (2007) found a similar distribution of Epsilonproteobacteria around the redoxcline.…”

Aerobic methanotrophy within the pelagic redox-zone of the Gotland Deep (central Baltic Sea)

“…Within the redox-zone of the central Baltic Sea, various biogeochemical processes have been identified, such as denitrification, ammonia oxidation, or dark CO 2 fixation (Labrenz et al, 2005;Jost et al, 2008;Glaubitz et al, 2009;Labrenz et al, 2010) and also microbial consumption of methane was proposed as mechanism explaining the strong methane decrease in this water layer (Schmale et al, 2010a). To gain information on the contribution of methanotrophic microorganisms to the POM within the redox-zone, we performed expression analyses of the methane monooxygenase gene (pmoA), and studied concentrations and distributions of bacteriohopanepolyols (BHPs).…”

Genome and physiology of a model Epsilonproteobacterium responsible for sulfide detoxification in marine oxygen depletion zones

“…Chemolithoautotrophic Epsilonproteobacteria are known mainly from deep-sea vent ecosystems, where they constitute a dominant and diverse bacterial group (11) with important roles in the cycling of carbon, nitrogen, and sulfur (12,13). However, Epsilonproteobacteria have also been detected in other marine sulfidic environments (9,(14)(15)(16), and are thought to be associated with chemoautotrophy and sulfur cycling.…”

“…Epsilonproteobacteria in the transition zone of suboxic and anoxic/sulfidic waters (the redoxline) are mainly comprised of a single phylogenetic cluster, Sulfurimonas subgroup GD17, which dominates chemoautotrophic production in the redoxcline (17). It has been proposed that these bacteria combine the oxidation of reduced sulfur compounds with denitrification (14). This chemoautotrophic denitrification has been shown to constitute a major nitrogen loss process in the water column of marine systems with a sulfidenitrate interface (18,19).…”