RESUMO
The sulfate-methane transition zone (SMTZ) is a widespread feature of continental margins, representing a diffusion-controlled interface where there is enhanced microbial activity. SMTZ microbial activity is commonly associated with the anaerobic oxidation of methane (AOM), which is carried out by syntrophic associations between sulfate-reducing bacteria and methane-oxidizing archaea. While our understanding of the microorganisms catalyzing AOM has advanced, the diversity and ecological role of the greater microbial assemblage associated with the SMTZ have not been well characterized. In this study, the microbial diversity above, within, and beneath the Santa Barbara Basin SMTZ was described. ANME-1-related archaeal phylotypes appear to be the primary methane oxidizers in the Santa Barbara Basin SMTZ, which was independently supported by exclusive recovery of related methyl coenzyme M reductase genes (mcrA). Sulfate-reducing Deltaproteobacteria phylotypes affiliated with the Desulfobacterales and Desulfosarcina-Desulfococcus clades were also enriched in the SMTZ, as confirmed by analysis of dissimilatory sulfite reductase (dsr) gene diversity. Statistical methods demonstrated that there was a close relationship between the microbial assemblages recovered from the two horizons associated with the geochemically defined SMTZ, which could be distinguished from microbial diversity recovered from the sulfate-replete overlying horizons and methane-rich sediment beneath the transition zone. Comparison of the Santa Barbara Basin SMTZ microbial assemblage to microbial assemblages of methane seeps and other organic matter-rich sedimentary environments suggests that bacterial groups not typically associated with AOM, such as Planctomycetes and candidate division JS1, are additionally enriched within the SMTZ and may represent a common bacterial signature of many SMTZ environments worldwide.
Assuntos
Archaea/classificação , Archaea/isolamento & purificação , Bactérias/classificação , Bactérias/isolamento & purificação , Sedimentos Geológicos/microbiologia , Proteínas Arqueais/genética , Proteínas de Bactérias/genética , Biodiversidade , California , DNA Arqueal/química , DNA Arqueal/genética , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Genes de RNAr , Sulfito de Hidrogênio Redutase/genética , Metano/metabolismo , Dados de Sequência Molecular , Oxirredução , Oxirredutases/genética , Filogenia , RNA Arqueal/genética , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Homologia de Sequência do Ácido Nucleico , Sulfatos/metabolismoRESUMO
Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate (CaCO3) particles. Here we estimate the in situ CaCO3 dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO2 on CaCO3 shell-forming species. CaCO3 dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO3 dissolution rate for the global oceans is approximately 0.5 +/- 0.2 petagrams of CaCO3-C per year, which is approximately 45 to 65% of the export production of CaCO3.