Abstract
The reduction of manganese oxide with sulfide in aquatic redox-stratified systems was previously considered to be mainly chemical, but recent isolation of the Black Sea isolate Candidatus Sulfurimonas marisnigri strain SoZ1 suggests an important role for biological catalyzation. Here we provide evidence from laboratory experiments, field data, and modeling that the latter process has a strong impact on redox zonation in the Black Sea. High relative abundances of Sulfurimonas spp. across the redoxcline in the central western gyre of the Black Sea coincided with the high-level expression of both the sulfide:quinone oxidoreductase gene (sqr, up to 93% expressed by Sulfurimonas spp.) and other sulfur oxidation genes. The cell-specific rate of manganese-coupled sulfide oxidation by Ca. S. marisnigri SoZ1 determined experimentally was combined with the in situ abundance of Sulfurimonas spp. in a one-dimensional numerical model to calculate the vertical sulfide distribution. Abiotic sulfide oxidation was too slow to counterbalance the sulfide flux from euxinic water. We conclude that microbially catalyzed Mn-dependent sulfide oxidation influences the element cycles of Mn, S, C, and N and therefore the prevalence of other functional groups of prokaryotes (e.g., anammox bacteria) in a sulfide-free, anoxic redox zone.
Highlights
In productive aquatic systems, the remineralization of organic matter regularly leads to oxygen (O2) deficiency and to anoxia or even euxinia
Our study investigated the potential contribution of extent microbial S2− oxidation by Sulfurimonas spp., using MnO2 as terminal electron acceptor, to the overall S2− oxidation in the redoxcline of the Black Sea
Field-based indications of S oxidation with MnO2 catalyzed by Sulfurimonas spp. in the Black Sea redoxcline In line with earlier research, an anoxic zone free of O2 and S2− spanning ~15 m was detected within the pelagic redoxcline of the FbmigCa.ra4islcnuiRglaartitieoSsnoZoo1ff,MtwhneaOsr2er-eamccoteiroddnieadrtaetudesiscnuoglefifHdfi2ecSieomnxtiicdkrao(tssi−eo1nn)sibonrysr.eCAsapf.toSenr. smpeaatsortiesinunrdiigzivraiitdiSouonaZlo1Sf.2−athsCeposinkaesmuspmalnepdsti(obrenadsoeafdrSroo2n−wti)nh, Sem2n−eodrremiummaolivzceaodlnwtSaa2i−sniccnoognnsMciednneOtrra2abtalinyodnssloCwwa.ietShr.. a non-linear least-squares fit using the displayed equation. c Reaction rate coefficients for the biological treatment with Ca
Summary
The remineralization of organic matter regularly leads to oxygen (O2) deficiency and to anoxia or even euxinia This transition is accompanied by the establishment of a pelagic redoxcline that separates the oxic surface from reducing bottom waters. In the Black Sea redoxcline, a layer in which O2 and sulfide (S2−, here defined as the sum of H2S, HS−, and S2−) are virtually absent, referred to as the “suboxic zone,” has been frequently reported since 1989 [1, 6, 8,9,10,11] This zone may span tens of meters but it is not well-defined, as some descriptions encompass waters with low concentrations of O2 (
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