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- Robador, Alberto, et al.
(författare)
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Activity and community structures of sulfate-reducing microorganisms in polar, temperate and tropical marine sediments
- 2016
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 10:4, s. 796-809
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Tidskriftsartikel (refereegranskat)abstract
- Temperature has a fundamental impact on the metabolic rates of microorganisms and strongly influences microbial ecology and biogeochemical cycling in the environment. In this study, we examined the catabolic temperature response of natural communities of sulfate-reducing microorganisms (SRM) in polar, temperate and tropical marine sediments. In short-term sediment incubation experiments with S-35-sulfate, we demonstrated how the cardinal temperatures for sulfate reduction correlate with mean annual sediment temperatures, indicating specific thermal adaptations of the dominant SRM in each of the investigated ecosystems. The community structure of putative SRM in the sediments, as revealed by pyrosequencing of bacterial 16S rRNA gene amplicons and phylogenetic assignment to known SRM taxa, consistently correlated with in situ temperatures, but not with sediment organic carbon concentrations or C:N ratios of organic matter. Additionally, several species-level SRM phylotypes of the class Deltaproteobacteria tended to co-occur at sites with similar mean annual temperatures, regardless of geographic distance. The observed temperature adaptations of SRM imply that environmental temperature is a major controlling variable for physiological selection and ecological and evolutionary differentiation of microbial communities.
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| 3. |
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| 4. |
- Robador, Alberto, et al.
(författare)
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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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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 74:8, s. 2316-2326
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Robador, Alberto, et al.
(författare)
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The impact of temperature change on the activity and community composition of sulfate-reducing abcteria in arctic versus temperate marine sediments
- 2009
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 11:7, s. 1692-1703
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Tidskriftsartikel (refereegranskat)abstract
- Arctic regions may be particularly sensitive to climate warming and, consequently, rates of carbon mineralization in warming marine sediment may also be affected. Using long-term (24 months) incubation experiments at 0°C, 10°C and 20°C, the temperature response of metabolic activity and community composition of sulfate-reducing bacteria were studied in the permanently cold sediment of north-western Svalbard (Arctic Ocean) and compared with a temperate habitat with seasonally varying temperature (German Bight, North Sea). Short-term 35S-sulfate tracer incubations in a temperature-gradient block (between −3.5°C and +40°C) were used to assess variations in sulfate reduction rates during the course of the experiment. Warming of arctic sediment resulted in a gradual increase of the temperature optima ( Topt) for sulfate reduction suggesting a positive selection of psychrotolerant/mesophilic sulfate-reducing bacteria (SRB). However, high rates at in situ temperatures compared with maximum rates showed the predominance of psychrophilic SRB even at high incubation temperatures. Changing apparent activation energies ( Ea) showed that increasing temperatures had an initial negative impact on sulfate reduction that was weaker after prolonged incubations, which could imply an acclimatization response rather than a selection process of the SRB community. The microbial community composition was analysed by targeting the 16S ribosomal RNA using catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH). The results showed the decline of specific groups of SRB and confirmed a strong impact of increasing temperatures on the microbial community composition of arctic sediment. Conversely, in seasonally changing sediment sulfate reduction rates and sulfate-reducing bacterial abundance changed little in response to changing temperature.
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| 7. |
- Sawicka, Joanna E., et al.
(författare)
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Effects of freeze-thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat
- 2010
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Ingår i: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:4, s. 585-594
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Tidskriftsartikel (refereegranskat)abstract
- Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from -5 to 4 degrees C, or abrupt, from -20 to 10 degrees C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring S-35 sulfate reduction rates (SRRs). Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degrees C, but activity resumed rapidly reaching >60 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (-20 versus 10 degrees C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations.
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| 8. |
- Sawicka, Joanna, et al.
(författare)
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Freeze-thaw effects on sulfate reduction rates and microbial community dynamics in Arctic sediments
- 2007
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Ingår i: Gesellschaft fuer Okologie 4th AQUASHIFT Workshop.
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Annual freeze-thaw cycles in Arctic regions are common for near-shore sediment at the turn of winter and spring, but the quantitative effects for carbon mineralization and microbial community composition are not well established. Repeated freeze-thaw treatments of sediment may affect the microbial community composition and slow down carbon mineralization rates. For our experiments, we targeted a key carbon mineralization process – bacterial sulfate reduction - to assess the susceptibility of turnover rates and community composition to repeated freeze-thaw cycles.
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