| 1. |
- Balmonte, John Paul, et al.
(author)
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A sea change in microbial enzymes : Heterogeneous latitudinal and depth-related gradients in bulk water and particle-associated enzymatic activities from 30 degrees S to 59 degrees N in the Pacific Ocean
- 2021
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In: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:9, s. 3489-3507
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Journal article (peer-reviewed)abstract
- Heterotrophic microbes initiate the degradation of high molecular weight organic matter using extracellular enzymes. Our understanding of differences in microbial enzymatic capabilities, especially among particle-associated taxa and in the deep ocean, is limited by a paucity of hydrolytic enzyme activity measurements. Here, we measured the activities of a broad range of hydrolytic enzymes (glucosidases, peptidases, polysaccharide hydrolases) in epipelagic to bathypelagic bulk water (nonsize-fractionated), and on particles (>= 3 mu m) along a 9800 km latitudinal transect from 30 degrees S in the South Pacific to 59 degrees N in the Bering Sea. Individual enzyme activities showed heterogeneous latitudinal and depth-related patterns, with varying biotic and abiotic correlates. With increasing latitude and decreasing temperature, lower laminarinase activities sharply contrasted with higher leucine aminopeptidase (leu-AMP) and chondroitin sulfate hydrolase activities in bulk water. Endopeptidases (chymotrypsins, trypsins) exhibited patchy spatial patterns, and their activities can exceed rates of the widely measured exopeptidase, leu-AMP. Compared to bulk water, particle-associated enzymatic profiles featured a greater relative importance of endopeptidases, as well as a broader spectrum of polysaccharide hydrolases in some locations, and latitudinal and depth-related trends that are likely consequences of varying particle fluxes. As water depth increased, enzymatic spectra on particles and in bulk water became narrower, and diverged more from one another. These distinct latitudinal and depth-related gradients of enzymatic activities underscore the biogeochemical consequences of emerging global patterns of microbial community structure and function, from surface to deep waters, and among particle-associated taxa.
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| 2. |
- Balmonte, John Paul, et al.
(author)
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Community structural differences shape microbial responses to high molecular weight organic matter
- 2019
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In: Environmental Microbiology. - : John Wiley & Sons. - 1462-2912 .- 1462-2920. ; 21:2, s. 557-571
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Journal article (peer-reviewed)abstract
- The extent to which differences in microbial community structure result in variations in organic matter (OM) degradation is not well understood. Here, we tested the hypothesis that distinct marine microbial communities from North Atlantic surface and bottom waters would exhibit varying compositional succession and functional shifts in response to the same pool of complex high molecular weight (HMW-OM). We also hypothesized that microbial communities would produce a broader spectrum of enzymes upon exposure to HMW-OM, indicating a greater potential to degrade these compounds than reflected by initial enzymatic activities. Our results show that community succession in amended mesocosms was congruent with cell growth, increased bacterial production and most notably, with substantial shifts in enzymatic activities. In all amended mesocosms, closely related taxa that were initially rare became dominant at time frames during which a broader spectrum of active enzymes were detected compared to initial timepoints, indicating a similar response among different communities. However, succession on the whole-community level, and the rates, spectra and progression of enzymatic activities, reveal robust differences among distinct communities from discrete water masses. These results underscore the crucial role of rare bacterial taxa in ocean carbon cycling and the importance of bacterial community structure for HMW-OM degradation.
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| 3. |
- Balmonte, John Paul, et al.
(author)
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Sharp contrasts between freshwater and marine microbial enzymatic capabilities, community composition, and DOM pools in a NE Greenland fjord
- 2020
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In: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 65:1, s. 77-95
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Journal article (peer-reviewed)abstract
- Increasing glacial discharge can lower salinity and alter organic matter (OM) supply in fjords, but assessing the biogeochemical effects of enhanced freshwater fluxes requires understanding of microbial interactions with OM across salinity gradients. Here, we examined microbial enzymatic capabilities-in bulk waters (nonsize-fractionated) and on particles (>= 1.6 mu m)-to hydrolyze common OM constituents (peptides, glucose, polysaccharides) along a freshwater-marine continuum within Tyrolerfjord-Young Sound. Bulk peptidase activities were up to 15-fold higher in the fjord than in glacial rivers, whereas bulk glucosidase activities in rivers were twofold greater, despite fourfold lower cell counts. Particle-associated glucosidase activities showed similar trends by salinity, but particle-associated peptidase activities were up to fivefold higher-or, for several peptidases, only detectable-in the fjord. Bulk polysaccharide hydrolase activities also exhibited freshwater-marine contrasts: xylan hydrolysis rates were fivefold higher in rivers, while chondroitin hydrolysis rates were 30-fold greater in the fjord. Contrasting enzymatic patterns paralleled variations in bacterial community structure, with most robust compositional shifts in river-to-fjord transitions, signifying a taxonomic and genetic basis for functional differences in freshwater and marine waters. However, distinct dissolved organic matter (DOM) pools across the salinity gradient, as well as a positive relationship between several enzymatic activities and DOM compounds, indicate that DOM supply exerts a more proximate control on microbial activities. Thus, differing microbial enzymatic capabilities, community structure, and DOM composition-interwoven with salinity and water mass origins-suggest that increased meltwater may alter OM retention and processing in fjords, changing the pool of OM supplied to coastal Arctic microbial communities.
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| 4. |
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| 5. |
- Hoarfrost, Adrienne, et al.
(author)
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Gulf Stream Ring Water Intrusion on the Mid-Atlantic Bight Continental Shelf Break Affects Microbially Driven Carbon Cycling
- 2019
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In: Frontiers in Marine Science. - : FRONTIERS MEDIA SA. - 2296-7745. ; 6
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Journal article (peer-reviewed)abstract
- Warm core, anticyclonic rings that spin off from the Gulf Stream circulate through the region directly offshore of the Mid-Atlantic Bight. If a warm core ring reaches the continental shelf break, its warm, highly saline water may subduct under cooler, fresher continental shelf surface water, resulting in subsurface waters at the shelf break and over the upper continental slope with high temperatures and salinities and distinct physical and chemical properties characteristic of Gulf Stream water. Such intruding water may also have microbial communities with distinct functional capacities, which may in turn affect the rate and nature of carbon cycling in this coastal/shelf environment. However, the functional capabilities of microbial communities within ring intrusion waters relative to surrounding continental shelf waters are largely unexplored. We investigated microbial community capacity to initiate organic matter remineralization by measuring hydrolysis of a suite of polysaccharide, peptide, and glucose substrates along a transect oriented across the Mid-Atlantic Bight shelf, shelf break, and upper slope. At the outermost sampling site, warm and salty water derived from a Gulf Stream warm core ring was present in the lower portion of the water column. This water exhibited hydrolytic capacities distinct from other sampling sites, and exhibited lower heterotrophic bacterial productivity overall. Warm core rings adjacent to the Mid-Atlantic Bight shelf have increased in frequency and duration in recent years. As the influence of warm core rings on the continental shelf and slope increases in the future, the rate and nature of organic matter remineralization on the continental shelf may also shift.
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| 6. |
- Hubert, Casey, et al.
(author)
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A constant flux of diverse thermophilic bacteria into the cold Arctic seabed
- 2009
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In: Science. - Washington : AAAS. - 0036-8075 .- 1095-9203. ; 325:18, s. 1541-1544
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Journal article (peer-reviewed)abstract
- Microorganisms have been repeatedly discovered in environments that do not support their metabolic activity. Identifying and quantifying these misplaced organisms can reveal dispersal mechanisms that shape natural microbial diversity. Using endospore germination experiments, we estimated a stable supply of thermophilic bacteria into permanently cold Arctic marine sediment at a rate exceeding 108 spores per square meter per year. These metabolically and phylogenetically diverse Firmicutes show no detectable activity at cold in situ temperatures but rapidly mineralize organic matter by hydrolysis, fermentation, and sulfate reduction upon induction at 50°C. The closest relatives to these bacteria come from warm subsurface petroleum reservoir and ocean crust ecosystems, suggesting that seabed fluid flow from these environments is delivering thermophiles to the cold ocean. These transport pathways may broadly influence microbial community composition in the marine environment.
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| 7. |
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| 8. |
- Julies, Elsabe M., et al.
(author)
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Organic Carbon Degradation in Anoxic Organic-Rich Shelf Sediments : Biogeochemical Rates and Microbial Abundance
- 2010
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In: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 27:4, s. 303-314
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Journal article (peer-reviewed)abstract
- Identifying and explaining bottlenecks in organic carbon mineralization and the persistence of organic matter in marine sediments remain challenging. This study aims to illuminate the process of carbon flow between microorganisms involved in the sedimentary microbial food chain in anoxic, organic-rich sediments of the central Namibian upwelling system, using biogeochemical rate measurements and abundances of Bacteroidetes, Gammaproteobacteria, and sulfate-reducing bacteria at two sampling stations. Sulfate reduction rates decreased by three orders of magnitude in the top 20 cm at one sampling station (280 nmol cm-3 d-1 - 0.1 nmol cm-3 d-1) and by a factor of 7 at the second station (65 nmol cm-3 d-1 - 9.6 nmol cm-3 d-1). However, rates of enzymatic hydrolysis decreased by less than a factor of three at both sampling stations for the polysaccharides laminarin (23 nmol cm-3 d-1- 8 nmol cm-3 d-1 and 22 nmol cm-3 d-1- 10 nmol cm-3 d-1) and pullulan (11 nmol cm-3 d-1- 4 nmol cm-3 d-1 and 8 nmol cm-3 d-1- 6 nmol cm-3 d-1). Increasing imbalance between carbon turnover by hydrolysis and terminal oxidation with depth, the steep decrease in cell specific activity of sulfate reducing bacteria with depth, low concentrations of volatile fatty acids (less than 15 M), and persistence of dissolved organic carbon, suggest decreasing bioavailability and substrate limitation with depth.
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| 9. |
- Kharbush, Jenan J., et al.
(author)
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Particulate Organic Carbon Deconstructed : Molecular and Chemical Composition of Particulate Organic Carbon in the Ocean
- 2020
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In: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 7
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Research review (peer-reviewed)abstract
- The dynamics of the particulate organic carbon (POC) pool in the ocean are central to the marine carbon cycle. POC is the link between surface primary production, the deep ocean, and sediments. The rate at which POC is degraded in the dark ocean can impact atmospheric CO2 concentration. Therefore, a central focus of marine organic geochemistry studies is to improve our understanding of POC distribution, composition, and cycling. The last few decades have seen improvements in analytical techniques that have greatly expanded what we can measure, both in terms of organic compound structural diversity and isotopic composition, and complementary molecular omics studies. Here we provide a brief overview of the autochthonous, allochthonous, and anthropogenic components comprising POC in the ocean. In addition, we highlight key needs for future research that will enable us to more effectively connect diverse data sources and link the identity and structural diversity of POC to its sources and transformation processes.
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| 10. |
- Robador, Alberto, et al.
(author)
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Temperature induced decoupling of enzymatic hydrolysis and carbon remineralization in long-term incubations of Arctic and temperate sediments
- 2010
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In: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 74:8, s. 2316-2326
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Journal article (peer-reviewed)abstract
- Extracellular enzymatic hydrolysis of high-molecular weight organic matter is the initial step in sedimentary organic carbon degradation and is often regarded as the rate-limiting step. Temperature effects on enzyme activities may therefore exert an indirect control on carbon mineralization. We explored the temperature sensitivity of enzymatic hydrolysis and its connection to subsequent steps in anoxic organic carbon degradation in long-term incubations of sediments from the Arctic and the North Sea. These sediments were incubated under anaerobic conditions for 24 months at temperatures of 0, 10, and 20 degrees C. The short-term temperature response of the active microbial community was tested in temperature gradient block incubations. The temperature optimum of extracellular enzymatic hydrolysis, as measured with a polysaccharide (chondroitin sulfate), differed between Arctic and temperate habitats by about 8-13 degrees C in fresh sediments and in sediments incubated for 24 months. In both Arctic and temperate sediments, the temperature response of chondroitin sulfate hydrolysis was initially similar to that of sulfate reduction. After 24 months, however, hydrolysis outpaced sulfate reduction rates, as demonstrated by increased concentrations of dissolved organic carbon (DOC) and total dissolved carbohydrates. This effect was stronger at higher incubation temperatures, particularly in the Arctic sediments. In all experiments, concentrations of volatile fatty acids (VFA) were low, indicating tight coupling between VFA production and consumption. Together, these data indicate that long-term incubation at elevated temperatures led to increased decoupling of hydrolytic DOC production relative to fermentation. Temperature increases in marine sedimentary environments may thus significantly affect the downstream carbon mineralization and lead to the increased formation of refractory DOC.
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