RESUMO
The release of vast quantities of sulfide from the sediment into the water column, known as a sulfidic event, has detrimental consequences on fish catches, including downstream effects on other linked element cycles. Despite being frequent occurrences in marine upwelling regions, our understanding of the factors that moderate sulfidic event formation and termination are still rudimentary. Here, we examined the biogeochemical and hydrodynamic conditions that underpinned the formation/termination of one of the largest sulfur plumes to be reported in the Peruvian upwelling zone. Consistent with previous research, we find that the sulfur-rich plume arose during the austral summer when anoxic conditions (i.e., oxygen and nitrate depletion) prevailed in waters overlying the upper shelf. Furthermore, the shelf sediments were organically charged and characterized by low iron-bound sulfur concentrations, further enabling the diffusion of benthic-generated sulfide into the water column. While these biogeochemical conditions provided a predicate to sulfidic event formation, we highlight that attenuations in local wind intensity served as an event trigger. Namely, interruptions in local wind speed constrained upwelling intensity, causing increased stratification over the upper shelf. Moreover, disturbances in local wind patterns likely placed additional constraints on wind-driven mesoscale eddy propagation, with feedback effects on coastal elemental sulfur plume (ESP) formation. We suggest ESP development occurs as a result of a complex interaction of biogeochemistry with regional hydrodynamics.
Assuntos
Hipóxia , Vento , Animais , Peru , Enxofre , Sulfetos , ÁguaRESUMO
Members of the epsilonproteobacterial genus Arcobacter have been identified to be potentially important sulfide oxidizers in marine coastal, seep, and stratified basin environments. In the highly productive upwelling waters off the coast of Peru, Arcobacter cells comprised 3 to 25% of the total microbial community at a near-shore station where sulfide concentrations exceeded 20 µM in bottom waters. From the chemocline where the Arcobacter population exceeded 106 cells ml-1 and where high rates of denitrification (up to 6.5 ± 0.4 µM N day-1) and dark carbon fixation (2.8 ± 0.2 µM C day-1) were measured, we isolated a previously uncultivated Arcobacter species, Arcobacter peruensis sp. nov. (BCCM LMG-31510). Genomic analysis showed that A. peruensis possesses genes encoding sulfide oxidation and denitrification pathways but lacks the ability to fix CO2 via autotrophic carbon fixation pathways. Genes encoding transporters for organic carbon compounds, however, were present in the A. peruensis genome. Physiological experiments demonstrated that A. peruensis grew best on a mix of sulfide, nitrate, and acetate. Isotope labeling experiments further verified that A. peruensis completely reduced nitrate to N2 and assimilated acetate but did not fix CO2, thus coupling heterotrophic growth to sulfide oxidation and denitrification. Single-cell nanoscale secondary ion mass spectrometry analysis of samples taken from shipboard isotope labeling experiments also confirmed that the Arcobacter population in situ did not substantially fix CO2 The efficient growth yield associated with the chemolithoheterotrophic metabolism of A. peruensis may allow this Arcobacter species to rapidly bloom in eutrophic and sulfide-rich waters off the coast of Peru.IMPORTANCE Our multidisciplinary approach provides new insights into the ecophysiology of a newly isolated environmental Arcobacter species, as well as the physiological flexibility within the Arcobacter genus and sulfide-oxidizing, denitrifying microbial communities within oceanic oxygen minimum zones (OMZs). The chemolithoheterotrophic species Arcobacter peruensis may play a substantial role in the diverse consortium of bacteria that is capable of coupling denitrification and fixed nitrogen loss to sulfide oxidation in eutrophic, sulfidic coastal waters. With increasing anthropogenic pressures on coastal regions, e.g., eutrophication and deoxygenation (D. Breitburg, L. A. Levin, A. Oschlies, M. Grégoire, et al., Science 359:eaam7240, 2018, https://doi.org/10.1126/science.aam7240), niches where sulfide-oxidizing, denitrifying heterotrophs such as A. peruensis thrive are likely to expand.
Assuntos
Arcobacter/isolamento & purificação , Arcobacter/metabolismo , Sedimentos Geológicos/microbiologia , Processos Heterotróficos/fisiologia , Água do Mar/microbiologia , Sulfetos/metabolismo , Arcobacter/genética , Arcobacter/crescimento & desenvolvimento , Biomassa , Carbono/metabolismo , Ciclo do Carbono , Desnitrificação , Marcação por Isótopo , Nitratos/metabolismo , Fixação de Nitrogênio , Oxirredução , Oxigênio/metabolismo , Peru , RNA Ribossômico 16S/genética , RNA Ribossômico 16S/isolamento & purificação , Água/química , Microbiologia da Água , Sequenciamento Completo do GenomaRESUMO
Members of the gammaproteobacterial clade SUP05 couple water column sulfide oxidation to nitrate reduction in sulfidic oxygen minimum zones (OMZs). Their abundance in offshore OMZ waters devoid of detectable sulfide has led to the suggestion that local sulfate reduction fuels SUP05-mediated sulfide oxidation in a so-called "cryptic sulfur cycle". We examined the distribution and metabolic capacity of SUP05 in Peru Upwelling waters, using a combination of oceanographic, molecular, biogeochemical and single-cell techniques. A single SUP05 species, U Thioglobus perditus, was found to be abundant and active in both sulfidic shelf and sulfide-free offshore OMZ waters. Our combined data indicated that mesoscale eddy-driven transport led to the dispersal of U T. perditus and elemental sulfur from the sulfidic shelf waters into the offshore OMZ region. This offshore transport of shelf waters provides an alternative explanation for the abundance and activity of sulfide-oxidizing denitrifying bacteria in sulfide-poor offshore OMZ waters.
Assuntos
Crescimento Quimioautotrófico/fisiologia , Gammaproteobacteria/metabolismo , Redes e Vias Metabólicas/fisiologia , Água do Mar/química , Enxofre/metabolismo , Organismos Aquáticos , Gammaproteobacteria/classificação , Gammaproteobacteria/crescimento & desenvolvimento , Nitrogênio/metabolismo , Oxirredução , Oxigênio/metabolismo , Peru , Filogenia , Água do Mar/microbiologiaRESUMO
The N2 -fixing (diazotrophic) community in marine ecosystems is dominated by non-cyanobacterial microorganisms. Yet, very little is known about their identity, function and ecological relevance due to a lack of cultured representatives. Here we report a novel heterotrophic diazotroph isolated from the oxygen minimum zone (OMZ) off Peru. The new species belongs to the genus Sagittula (Rhodobacteraceae, Alphaproteobacteria) and its capability to fix N2 was confirmed in laboratory experiments. Genome sequencing revealed that it is a strict heterotroph with a high versatility in substrate utilization and energy acquisition mechanisms. Pathways for sulfide oxidation and nitrite reduction to nitrous oxide are encoded in the genome and might explain the presence throughout the Peruvian OMZ. The genome further indicates that this novel organism could be in direct interaction with other microbes or particles. NanoSIMS analyses were used to compare the metabolic potential of S. castanea with single-cell activity in situ; however, N2 fixation by this diazotroph could not be detected at the isolation site. While the biogeochemical impact of S. castanea is yet to be resolved, its abundance and widespread distribution suggests that its potential to contribute to the marine N input could be significant at a larger geographical scale.
Assuntos
Metabolismo Energético/fisiologia , Fixação de Nitrogênio/fisiologia , Rhodobacteraceae/classificação , Rhodobacteraceae/metabolismo , Anaerobiose , Metabolismo Energético/genética , Genoma Bacteriano/genética , Processos Heterotróficos , Nitritos/metabolismo , Fixação de Nitrogênio/genética , Oxirredução , Oxigênio/metabolismo , Peru , Rhodobacteraceae/isolamento & purificação , Água do Mar/microbiologia , Sulfetos/metabolismoRESUMO
The eastern tropical South Pacific (ETSP) upwelling region is one of the ocean's largest sinks of fixed nitrogen, which is lost as N2 via the anaerobic processes of anammox and denitrification. One-third of nitrogen loss occurs in productive shelf waters stimulated by organic matter export as a result of eastern boundary upwelling. Offshore, nitrogen loss rates are lower, but due to its sheer size this area accounts for ~70% of ETSP nitrogen loss. How nitrogen loss and primary production are regulated in the offshore ETSP region where coastal upwelling is less influential remains unclear. Mesoscale eddies, ubiquitous in the ETSP region, have been suggested to enhance vertical nutrient transport and thereby regulate primary productivity and hence organic matter export. Here, we investigated the impact of mesoscale eddies on anammox and denitrification activity using 15N-labelled in situ incubation experiments. Anammox was shown to be the dominant nitrogen loss process, but varied across the eddy, whereas denitrification was below detection at all stations. Anammox rates at the eddy periphery were greater than at the center. Similarly, depth-integrated chlorophyll paralleled anammox activity, increasing at the periphery relative to the eddy center; suggestive of enhanced organic matter export along the periphery supporting nitrogen loss. This can be attributed to enhanced vertical nutrient transport caused by an eddy-driven submesoscale mechanism operating at the eddy periphery. In the ETSP region, the widespread distribution of eddies and the large heterogeneity observed in anammox rates from a compilation of stations suggests that eddy-driven vertical nutrient transport may regulate offshore primary production and thereby nitrogen loss.