5,989 research outputs found
Adaptation of psychrophilic and psychrotrophic sulfate-reducing bacteria to permanently cold marine environments
The potential for sulfate reduction at low temperatures was examined in two different cold marine sediments, Mariager Fjord (Denmark), which is permanently cold (3 to 6 degrees C) but surrounded by seasonally warmer environments, and the Weddell Sea (Antarctica), which is permanently below 0 degrees C. The rates of sulfate reduction were measured by the (SO42-)-S-35 tracer technique at different experimental temperatures in sediment slurries, In sediment slurries from Mariager Fjord, sulfate reduction showed a mesophilic temperature response which was comparable to that of other temperate environments, In sediment slurries from Antarctica, the metabolic activity of psychrotrophic bacteria was observed with a respiration optimum at 18 to 19 degrees C during short-term incubations, However, over a 1-week incubation, the highest respiration rate was observed at 12.5 degrees C. Growth of the bacterial population at the optimal growth temperature could be an explanation for the low temperature optimum of the measured sulfate reduction, The potential for sulfate reduction was highest at temperatures well above the in situ temperature in all experiments, The results frorn sediment incubations were compared with those obtained from pure cultures of sulfate-reducing bacteria by using the psychrotrophic strain Itk10 and the mesophilic strain ak30. The psychrotrophic strain reduced sulfate optimally at 28 degrees C in short-term incubations, even though it could not grow at temperatures above 24 degrees C. Furthermore, this strain showed its highest growth yield between 0 and 12 degrees C. In contrast, the mesophilic strain ak30 respired and grew optimally and showed its highest growth yield at 30 to 35 degrees C
High Frame-rate Imaging Based Photometry, Photometric Reduction of Data from Electron-multiplying Charge Coupled Devices (EMCCDs)
The EMCCD is a type of CCD that delivers fast readout times and negligible
readout noise, making it an ideal detector for high frame rate applications
which improve resolution, like lucky imaging or shift-and-add. This improvement
in resolution can potentially improve the photometry of faint stars in
extremely crowded fields significantly by alleviating crowding. Alleviating
crowding is a prerequisite for observing gravitational microlensing in main
sequence stars towards the galactic bulge. However, the photometric stability
of this device has not been assessed. The EMCCD has sources of noise not found
in conventional CCDs, and new methods for handling these must be developed.
We aim to investigate how the normal photometric reduction steps from
conventional CCDs should be adjusted to be applicable to EMCCD data. One
complication is that a bias frame cannot be obtained conventionally, as the
output from an EMCCD is not normally distributed. Also, the readout process
generates spurious charges in any CCD, but in EMCCD data, these charges are
visible as opposed to the conventional CCD. Furthermore we aim to eliminate the
photon waste associated with lucky imaging by combining this method with
shift-and-add.
A simple probabilistic model for the dark output of an EMCCD is developed.
Fitting this model with the expectation-maximization algorithm allows us to
estimate the bias, readout noise, amplification, and spurious charge rate per
pixel and thus correct for these phenomena. To investigate the stability of the
photometry, corrected frames of a crowded field are reduced with a PSF fitting
photometry package, where a lucky image is used as a reference.
We find that it is possible to develop an algorithm that elegantly reduces
EMCCD data and produces stable photometry at the 1% level in an extremely
crowded field.Comment: Submitted to Astronomy and Astrophysic
Environmental control on anaerobic oxidation of methane in the gassy sediments of Eckernforde Bay (German Baltic)
We investigated the effect of seasonal environmental changes on the rate and distribution of anaerobic oxidation of methane (AOM) in Eckernforde Bay sediments (German Baltic Sea) and identified organisms that are likely to be involved in the process. Surface sediments were sampled during September and March. Field rates of AOM and sulfate reduction (SR) were measured with radiotracer methods. Additional parameters were determined that potentially influence AOM, i.e., temperature, salinity, methane, sulfate, and chlorophyll a. Methanogenesis as well as potential rates of AOM and aerobic oxidation of methane were measured in vitro. AOM changed seasonally within the upper 20 cm of the sediment, with rates being between 1 and 14 nmol cm−3 d−1. Its distribution is suggested to be controlled by oxygen and sulfate penetration, temperature, as well as methane supply, leading to a shallow AOM zone during the warm productive season and to a slightly deeper AOM zone during the cold winter season. Rising methane bubbles apparently fed AOM above the sulfate‐methane transition. Methanosarcinales‐related anaerobic methanotrophs (ANME‐2), identified with fluorescence in situ hybridization, is suggested to mediate AOM in Eckernforde Bay. These archaea are known also from other marine methane‐rich locations. However, they were not directly associated with sulfate‐reducing bacteria. AOM is possibly mediated solely by these archaea that show a mesophilic physiology according to the seasonal temperature changes in Eckernforde Bay
Desulfuromonas svalbardensis sp nov and Desulfuromusa ferrireducens sp nov., psychrophilic, Fe(III)-reducing bacteria isolated from Arctic sediments, Svalbard
Two psychrophilic, Gram-negative, rod-shaped, motile bacteria (strains 112T and 102T) that conserved energy from dissimilatory Fe(III) reduction concomitant with acetate oxidation were isolated from permanently cold Arctic marine sediments. Both strains grew at temperatures down to -2 degrees C, with respective temperature optima of 14 degrees C and 14-17 degrees C for strains 112T and 102T. The isolated strains reduced Fe(III) using common fermentation products such as acetate, lactate, propionate, formate or hydrogen as electron donors, and they also grew with fumarate as the sole substrate. As alternatives to Fe(III), they reduced fumarate, S0 and Mn(IV). Based on 16S rRNA gene sequence similarity, strain 112T was most closely related to Desulfuromonas acetoxidans (97.0 %) and Desulfuromonas thiophila NZ27T (95.5 %), and strain 102T to Malonomonas rubra Gra Mal 1T (96.3 %) and Desulfuromusa succinoxidans GylacT (95.9 %) within the Deltaproteobacteria. Strains 112T and 102T therefore represent novel species, for which the names Desulfuromonas svalbardensis sp. nov. (type strain 112T=DSM 16958T=JCM 12927T) and Desulfuromusa ferrireducens sp. nov. (type strain 102T=DSM 16956T=JCM 12926T) are proposed
Sulfide assimilation by ectosymbionts of the sessile ciliate, Zoothamnium niveum
We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat. The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs
Manipulating the torsion of molecules by strong laser pulses
A proof-of-principle experiment is reported, where torsional motion of a
molecule, consisting of a pair of phenyl rings, is induced by strong laser
pulses. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis,
connecting the two phenyl rings, allowing a perpendicularly polarized, intense
femtosecond pulse to initiate torsional motion accompanied by an overall
rotation about the fixed axis. The induced motion is monitored by femtosecond
time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for
and generalizes the experimental findings.Comment: 4 pages, 4 figures, submitted to PRL; Major revision of the
presentation of the material; Correction of ion labels in Fig. 2(a
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