12 research outputs found
Spot evolution in the eclipsing binary CoRoT 105895502
Stellar activity is ubiquitous in late-type stars. The special geometry of
eclipsing binary systems is particularly advantageous to study the stellar
surfaces and activity. We present a detailed study of the 145 d CoRoT light
curve of the short-period eclipsing binary CoRoT 105895502. By means of
light-curve modeling with Nightfall, we determine the orbital period, effective
temperature, Roche-lobe filling factors, mass ratio, and orbital inclination of
CoRoT 105895502 and analyze the temporal behavior of starspots in the system.
Our analysis shows one comparably short-lived (about 40 d) starspot, remaining
quasi-stationary in the binary frame, and one starspot showing prograde motion
at a rate of 2.3 deg per day, whose lifetime exceeds the duration of the
observation. In the CoRoT band, starspots account for as much as 0.6 % of the
quadrature flux of CoRoT 105895502, however we cannot attribute the spots to
individual binary components with certainty. Our findings can be explained by
differential rotation, asynchronous stellar rotation, or systematic spot
evolution.Comment: Accepted in A&
(Per)chlorate reduction by an acetogenic bacterium, Sporomusa sp., isolated from an underground gas storage
A mesophilic bacterium, strain An4, was isolated from an underground gas storage reservoir with methanol as substrate and perchlorate as electron acceptor. Cells were Gram-negative, spore-forming, straight to curved rods, 0.5â0.8 Όm in diameter, and 2â8 Όm in length, growing as single cells or in pairs. The cells grew optimally at 37°C, and the pH optimum was around 7. Strain An4 converted various alcohols, organic acids, fructose, acetoin, and H2/CO2 to acetate, usually as the only product. Succinate was decarboxylated to propionate. The isolate was able to respire with (per)chlorate, nitrate, and CO2. The G+C content of the DNA was 42.6 mol%. Based on the 16S rRNA gene sequence analysis, strain An4 was most closely related to Sporomusa ovata (98% similarity). The bacterium reduced perchlorate and chlorate completely to chloride. Key enzymes, perchlorate reductase and chlorite dismutase, were detected in cell-free extracts
Characterization of a Heme-Dependent Catalase from Methanobrevibacter arboriphilus
Recently it was reported that methanogens of the genus Methanobrevibacter exhibit catalase activity. This was surprising, since Methanobrevibacter species belong to the order Methanobacteriales, which are known not to contain cytochromes and to lack the ability to synthesize heme. We report here that Methanobrevibacter arboriphilus strains AZ and DH1 contained catalase activity only when the growth medium was supplemented with hemin. The heme catalase was purified and characterized, and the encoding gene was cloned. The amino acid sequence of the catalase from the methanogens is most similar to that of Methanosarcina barkeri