During theDeepwater Horizonoil well blowout in the Gulf of Mexico, the application of 7 million liters of chemical dispersants aimed to stimulate microbial crude oil degradation by increasing the ...bioavailability of oil compounds. However, the effects of dispersants on oil biodegradation rates are debated. In laboratory experiments, we simulated environmental conditions comparable to the hydrocarbon-rich, 1,100 m deep plume that formed during theDeepwater Horizondischarge. The presence of dispersant significantly altered the microbial community composition through selection for potential dispersant-degradingColwellia,which also bloomed in situ in Gulf deep waters during the discharge. In contrast, oil addition to deepwater samples in the absence of dispersant stimulated growth of natural hydrocarbon-degradingMarinobacter.In these deepwater microcosm experiments, dispersants did not enhance heterotrophic microbial activity or hydrocarbon oxidation rates. An experiment with surface seawater from an anthropogenically derived oil slick corroborated the deepwater microcosm results as inhibition of hydrocarbon turnover was observed in the presence of dispersants, suggesting that the microcosm findings are broadly applicable across marine habitats. Extrapolating this comprehensive dataset to real world scenarios questions whether dispersants stimulate microbial oil degradation in deep ocean waters and instead highlights that dispersants can exert a negative effect on microbial hydrocarbon degradation rates.
Cable bacteria are long, filamentous, multicellular bacteria that grow in marine sediments and couple sulfide oxidation to oxygen reduction over centimetre‐scale distances via long‐distance electron ...transport. Cable bacteria can strongly modify biogeochemical cycling and may affect microbial community networks. Here we examine interspecific interactions with marine cable bacteria (Ca. Electrothrix) by monitoring the succession of 16S rRNA amplicons (DNA and RNA) and cell abundance across depth and time, contrasting sediments with and without cable bacteria growth. In the oxic zone, cable bacteria activity was positively associated with abundant predatory bacteria (Bdellovibrionota, Myxococcota, Bradymonadales), indicating putative predation on cathodic cells. At suboxic depths, cable bacteria activity was positively associated with sulfate‐reducing and magnetotactic bacteria, consistent with cable bacteria functioning as ecosystem engineers that modify their local biogeochemical environment, benefitting certain microbes. Cable bacteria activity was negatively associated with chemoautotrophic sulfur‐oxidizing Gammaproteobacteria (Thiogranum, Sedimenticola) at oxic depths, suggesting competition, and positively correlated with these taxa at suboxic depths, suggesting syntrophy and/or facilitation. These observations are consistent with chemoautotrophic sulfur oxidizers benefitting from an oxidizing potential imparted by cable bacteria at suboxic depths, possibly by using cable bacteria as acceptors for electrons or electron equivalents, but by an as yet enigmatic mechanism.
Seasonal oxygen depletion (hypoxia) in coastal bottom waters can lead to the release and persistence of free sulfide (euxinia), which is highly detrimental to marine life. Although coastal hypoxia is ...relatively common, reports of euxinia are less frequent, which suggests that certain environmental controls can delay the onset of euxinia. However, these controls and their prevalence are poorly understood. Here we present field observations from a seasonally hypoxic marine basin (Grevelingen, The Netherlands), which suggest that the activity of cable bacteria, a recently discovered group of sulfur-oxidizingmicroorganisms inducing long-distance electron transport, can delay the onset of euxinia in coastal waters. Our results reveal a remarkable seasonal succession of sulfur cycling pathways, which was observed over multiple years. Cable bacteria dominate the sediment geochemistry in winter, whereas, after the summer hypoxia,Beggiatoaceaemats colonize the sediment. The specific electrogenic metabolism of cable bacteria generates a large buffer of sedimentary iron oxides before the onset of summer hypoxia, which captures free sulfide in the surface sediment, thus likely preventing the development of bottom water euxinia. As cable bacteria are present in many seasonally hypoxic systems, this euxinia-preventing firewall mechanism could be widely active, and may explain why euxinia is relatively infrequently observed in the coastal ocean.
Plastic debris in the coastal environment is subject to complex and poorly characterized weathering processes. To better understand how key environmental factors affect plastic degradation in a ...coastal zone, we conducted an in situ experiment. We deployed strips of high density polyethylene (HDPE) and polystyrene (PS) in paired coastal areas of contrasting conditions (hydrodynamic activity: erosional or depositional; water depths: subtidal or intertidal). Strips were collected after environmental exposures at 4, 8, and 43 weeks and analyzed for change in mass, algal biofilm growth, and imaged by petrographic and electron microscopy (SEM-EDS). Significant surface erosion was evident on both polymers, and was more rapid and more extensive with PS. Degradation of PS was responsive to intensity of hydrodynamic activity, and was greater at intertidal depths, highlighting the critical role played by photo-oxidation in the coastal zone, and suggesting that algal biofilms may slow degradation by playing a photo-protective role.
•Degradation of PS was faster than HDPE at all deployment locations.•Numerous grooves and pitting indicated surface weathering of HDPE.•PS surface weathering and fragmentation was strongly responsive to coastal exposure.•Significantly greater degradation of PS under erosional and intertidal conditions.•Greater biofilm development at subtidal depths, regardless of plastic type.
Recently, a novel “electrogenic” type of sulfur oxidation has been documented in marine sediments, whereby long filamentous cable bacteria are generating electrical currents over centimeter-scale ...distances. Here we propose a numerical model description that is capable of quantitatively simulating the solute depth profiles and biogeochemical transformations in such electro-active marine sediments. The model is based on a conventional reactive transport description of marine sediments, which is extended with a new model formulation for the long-distance electron transport induced by the cable bacteria. The mechanism of electron hopping is implemented to describe the electron transport along the longitudinal axis of the microbial filaments. We demonstrate that this model is capable of reproducing the observed geochemical fingerprint of electrogenic sulfur oxidation, which consists of a characteristic set of O2, pH and H2S depth profiles. Our simulation results suggest that the cable bacteria must have a high affinity for both oxygen and sulfide, and that intensive cryptic sulfur cycling takes place within the suboxic zone. A sensitivity analysis shows how electrogenic sulfur oxidation strongly impacts the biogeochemical cycling of sulfur, iron, carbon and calcium in marine sediments.
In this study, we examined the succession of soil microbial communities across a chronosequence of newly constructed salt marshes constructed primarily of fine-grained dredge material, using 16S rRNA ...amplicon sequences. Alpha diversity in the subsurface horizons was initially low and increased to reference levels within 3 years of marsh construction, while alpha diversity in the newly accumulating organic matter-rich surface soils was initially high and remained unchanged. Microbial community succession was fastest in the surface horizon (~ 24 years to reference equivalency) and became progressively slower with depth in the subsurface horizons (~ 30–67 years). Random forest linear regression analysis was used to identify important taxa driving the trajectories toward reference conditions. In the parent material, putative sulfate-reducers (
Desulfobacterota
), methanogens (
Crenarchaeota
, especially
Methanosaeta
), and fermenters (
Chloroflexi
and
Clostridia
) increased over time, suggesting an enrichment of these metabolisms over time, similar to natural marshes. Concurrently in the surface soils, the relative abundances of putative methane-, methyl-, and sulfide oxidizers, especially among
Gammaproteobacteria
, increased over time, suggesting the co-development of sulfide and methane removal metabolisms in marsh soils. Finally, we observed that the surface soil communities at one of the marshes did not follow the trajectory of the others, exhibiting a greater relative abundance of anaerobic taxa. Uniquely in this dataset, this marsh was developing signs of excessive inundation stress in terms of vegetation coverage and soil geochemistry. Therefore, we suggest that soil microbial community structure may be effective bioindicators of salt marsh inundation and are worthy of further targeted investigation.
Recently, a novel electrogenic type of sulphur oxidation was documented in marine sediments, whereby filamentous cable bacteria (Desulfobulbaceae) are mediating electron transport over cm-scale ...distances. These cable bacteria are capable of developing an extensive network within days, implying a highly efficient carbon acquisition strategy. Presently, the carbon metabolism of cable bacteria is unknown, and hence we adopted a multidisciplinary approach to study the carbon substrate utilization of both cable bacteria and associated microbial community in sediment incubations. Fluorescence in situ hybridization showed rapid downward growth of cable bacteria, concomitant with high rates of electrogenic sulphur oxidation, as quantified by microelectrode profiling. We studied heterotrophy and autotrophy by following (13)C-propionate and -bicarbonate incorporation into bacterial fatty acids. This biomarker analysis showed that propionate uptake was limited to fatty acid signatures typical for the genus Desulfobulbus. The nanoscale secondary ion mass spectrometry analysis confirmed heterotrophic rather than autotrophic growth of cable bacteria. Still, high bicarbonate uptake was observed in concert with the development of cable bacteria. Clone libraries of 16S complementary DNA showed numerous sequences associated to chemoautotrophic sulphur-oxidizing Epsilon- and Gammaproteobacteria, whereas (13)C-bicarbonate biomarker labelling suggested that these sulphur-oxidizing bacteria were active far below the oxygen penetration. A targeted manipulation experiment demonstrated that chemoautotrophic carbon fixation was tightly linked to the heterotrophic activity of the cable bacteria down to cm depth. Overall, the results suggest that electrogenic sulphur oxidation is performed by a microbial consortium, consisting of chemoorganotrophic cable bacteria and chemolithoautotrophic Epsilon- and Gammaproteobacteria. The metabolic linkage between these two groups is presently unknown and needs further study.
Recently, a novel mode of sulphur oxidation was described in marine sediments, in which sulphide oxidation in deeper anoxic layers was electrically coupled to oxygen reduction at the sediment ...surface. Subsequent experimental evidence identified that long filamentous bacteria belonging to the family Desulfobulbaceae likely mediated the electron transport across the centimetre-scale distances. Such long-range electron transfer challenges some long-held views in microbial ecology and could have profound implications for sulphur cycling in marine sediments. But, so far, this process of electrogenic sulphur oxidation has been documented only in laboratory experiments and so its imprint on the seafloor remains unknown. Here we show that the geochemical signature of electrogenic sulphur oxidation occurs in a variety of coastal sediment environments, including a salt marsh, a seasonally hypoxic basin, and a subtidal coastal mud plain. In all cases, electrogenic sulphur oxidation was detected together with an abundance of Desulfobulbaceae filaments. Complementary laboratory experiments in intertidal sands demonstrated that mechanical disturbance by bioturbating fauna destroys the electrogenic sulphur oxidation signal. A survey of published geochemical data and 16S rRNA gene sequences identified that electrogenic sulphide oxidation is likely present in a variety of marine sediments with high sulphide generation and restricted bioturbation, such as mangrove swamps, aquaculture areas, seasonally hypoxic basins, cold sulphide seeps and possibly hydrothermal vent environments. This study shows for the first time that electrogenic sulphur oxidation occurs in a wide range of marine sediments and that bioturbation may exert a dominant control on its natural distribution.
Seasonal hypoxia refers to the oxygen depletion that occurs in summer in the bottom water of stratified systems, and is increasingly observed in coastal areas worldwide. The process induces a ...seasonal cycle on the biogeochemistry of the underlying sediments, which remains poorly quantified. Here, we investigated the sedimentary oxygen consumption within Lake Grevelingen (The Netherlands), a saline coastal reservoir that is impacted by yearly recurrent bottom water hypoxia. Monthly sampling campaigns were conducted throughout 2012 at three sites along a depth gradient. Macrofauna sampling and sediment profile imaging demonstrated how summer hypoxia strongly impacts the benthic communities below 15 m of water depth. Benthic fluxes of oxygen, dissolved inorganic carbon, total alkalinity, and ammonium were determined by closed core incubations, while oxygen depth profiles were recorded by microsensor profiling of sediment cores. Our results reveal a pronounced seasonality in the sedimentary oxygen consumption. Low uptake rates in summer were caused by oxygen limitation, and resulted in the build-up of an “oxygen debt” through the accumulation of reduced iron sulfides. Highest oxygen uptake rates were recorded in fall, linked to the reoxidation of the pool of iron sulfides in the top layer. However, uptake rates remained unexpectedly high during winter and early spring, likely associated with the oxidation of iron sulfides down to centimeters depth due to the electrogenic sulfur oxidation by cable bacteria. Overall, our results suggest that the sedimentary oxygen dynamic in seasonally hypoxic coastal systems is characterized by a strongly amplified “oxygen debt” dynamics induced by cable bacteria.
Cladophora glomerata (L.) Kütz. is, potentially, the most widely distributed macroalga throughout the world's freshwater ecosystems. C. glomerata has been described throughout North America, Europe, ...the Atlantic Islands, the Caribbean Islands, Asia, Africa, Australia and New Zealand, and the Pacific Islands. Cladophora blooms were a common feature of the lower North American Great Lakes (Erie, Michigan, Ontario) from the 1950s through the early 1980s and were largely eradicated through the implementation of a multibillion-dollar phosphorus (P) abatement program. The return of widespread blooms in these lakes since the mid-1990s, however, was not associated with increases in P loading. Instead, current evidence indicates that the resurgence in blooms was directly related to ecosystem level changes in substratum availability, water clarity, and P recycling associated with the establishment of dense colonies of invasive dreissenid mussels. These results support the hypothesis that dreissenid mussel invasions may induce dramatic shifts in energy and nutrient flow from pelagic zones to the benthic zone.
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