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Calorimetric measurements of heat flow and total heat prodn. can inform on the energetics of microbial activity. Nanocalorimetry permits such investigations in environments (natural or lab.) where energy supplies are extremely limited and/or very few cells are metabolically active. We will present nanocalorimetry data obtained during incubations of unamended formation fluids from the oceanic crust (∼300 m deep at the Juan de Fuca Ridge flank) and the continental subsurface (∼1500 m deep at the Sanford Underground Research Facility in South Dakota). Enthalpic responses by the resident microbial communities to addn. of org. carbon, inorg. electron donors, and nutrients will also be discussed. We further used nanocalorimetry on lab. expts. with model organisms to det. the energetics assocd. with carbon, electron donor, and nutrient limitations. For example, with a sulfate reducing bacterium, we quantified the significant cost during the metabolic transition from ammonium assimilation to N_2 fixation. In another set of expts., with an evolving population of E. coli mutants that express the GASP (growth advantage in stationary phase) phenotype, we recorded distinct heat events assocd. with the emergence of nascent mutant populations.

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.

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., authorCount :5

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.

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.

The present work analyzes the potential impact of anticipated global warming on the bacterial carbon cycling in marine shelf sediments. Current changes of the marine biological carbon cycle in response to climate warming in different regions of the world ocean are closely coupled to the response of bacteria to environmental temperatures. We investigated the correlation between ambient temperatures and the physiological adaptations, in terms of energy metabolism, of sulfatereducing bacteria (SRB) in polar, temperate and tropical sediments. In short-term sediment incubations in a temperature gradient block, sulfate-reduction rates (SRR) were measured using 35S-sulfate. Resulting temperature response profiles were used to examine the competitiveness of SRB, in terms of relative SRR of maximal potential rates, the temperature dependence for energy metabolism of SRB and the correlation of cardinal temperatures of sulfate reduction and sediment temperatures. We observed that SRB in polar sediments are more competitive than their counterparts in warmer habitats at similar low temperatures. Although metabolic rates in warmer latitudes exhibited higher temperature dependence below 8-18à °C, optimal temperature conditions for sulfate reduction in these environments are closer to their ambient temperatures resulting in a higher competitiveness at in situ conditions. Together, these observations imply that biography and, consequently, environmental temperature variability play an important role in the physiological selection and divergence of microbiota in different latitudes. Over a long-term (2 year) temperature incubation experiment, we measured 35S-SRR in a temperature gradient block and used CARDFISH of sulfate-reducing bacteria to describe the temperature control of carbon mineralization rates via sulfate reduction in Arctic marine sediments in comparison to a temperate habitat. This study is innovative in that we examine the consequences of temperature shifts by investi

The present work analyzes the potential impact of anticipated global warming on the bacterial carbon cycling in marine shelf sediments. Current changes of the marine biological carbon cycle in response to climate warming in different regions of the world ocean are closely coupled to the response of bacteria to environmental temperatures. We investigated the correlation between ambient temperatures and the physiological adaptations, in terms of energy metabolism, of sulfatereducing bacteria (SRB) in polar, temperate and tropical sediments. In short-term sediment incubations in a temperature gradient block, sulfate-reduction rates (SRR) were measured using 35S-sulfate. Resulting temperature response profiles were used to examine the competitiveness of SRB, in terms of relative SRR of maximal potential rates, the temperature dependence for energy metabolism of SRB and the correlation of cardinal temperatures of sulfate reduction and sediment temperatures. We observed that SRB in polar sediments are more competitive than their counterparts in warmer habitats at similar low temperatures. Although metabolic rates in warmer latitudes exhibited higher temperature dependence below 8-18à °C, optimal temperature conditions for sulfate reduction in these environments are closer to their ambient temperatures resulting in a higher competitiveness at in situ conditions. Together, these observations imply that biography and, consequently, environmental temperature variability play an important role in the physiological selection and divergence of microbiota in different latitudes. Over a long-term (2 year) temperature incubation experiment, we measured 35S-SRR in a temperature gradient block and used CARDFISH of sulfate-reducing bacteria to describe the temperature control of carbon mineralization rates via sulfate reduction in Arctic marine sediments in comparison to a temperate habitat. This study is innovative in that we examine the consequences of temperature shifts by investi

The present work analyzes the potential impact of anticipated global warming on the bacterial carbon cycling in marine shelf sediments. Current changes of the marine biological carbon cycle in response to climate warming in different regions of the world ocean are closely coupled to the response of bacteria to environmental temperatures. We investigated the correlation between ambient temperatures and the physiological adaptations, in terms of energy metabolism, of sulfatereducing bacteria (SRB) in polar, temperate and tropical sediments. In short-term sediment incubations in a temperature gradient block, sulfate-reduction rates (SRR) were measured using 35S-sulfate. Resulting temperature response profiles were used to examine the competitiveness of SRB, in terms of relative SRR of maximal potential rates, the temperature dependence for energy metabolism of SRB and the correlation of cardinal temperatures of sulfate reduction and sediment temperatures. We observed that SRB in polar sediments are more competitive than their counterparts in warmer habitats at similar low temperatures. Although metabolic rates in warmer latitudes exhibited higher temperature dependence below 8-18à °C, optimal temperature conditions for sulfate reduction in these environments are closer to their ambient temperatures resulting in a higher competitiveness at in situ conditions. Together, these observations imply that biography and, consequently, environmental temperature variability play an important role in the physiological selection and divergence of microbiota in different latitudes. Over a long-term (2 year) temperature incubation experiment, we measured 35S-SRR in a temperature gradient block and used CARDFISH of sulfate-reducing bacteria to describe the temperature control of carbon mineralization rates via sulfate reduction in Arctic marine sediments in comparison to a temperate habitat. This study is innovative in that we examine the consequences of temperature shifts by investi