Hydrogen oxidation rates were measured in a neutral compost soil and an acidic sandy loam at H2 mixing ratios of 0.01 to 5000 ppmv. The kinetics were biphasic showing two different Km values for H2, one at about 10–40 nM dissolved H2, the other at about 1.2–1.4 μM H2. The low‐Km activity was less sensitive to chloroform fumigation than the high‐Km activity. If sterile soil was amended with Paracoccus denitrificans or a H2‐oxidizing strain isolated from compost soil, it exhibited only a high‐Km (0.7–0.9 μM) activity. It also failed to utilize H2 mixing ratios below a threshold of 1.6–3.0 ppmv H2 (160–300 mPa). A similar result was obtained when fresh soil samples were suspended in water, and H2 oxidation was determined from the decrease of dissolved H2. However, H2 was again utilized to mixing ratios lower than 0.05 ppmv, if the supernatant of the soil suspension or the settled soil particles were dried onto sterile soil or purified quarz sand. Obviously, soils contain two different activities for oxidation of H2: (1) a high‐Km, high‐threshold activity which apparently is due to aerobic H2‐oxidizing bacteria, and (2) a low‐Km, low‐threshold activity whose origin is unknown but presumably is due to soil enzymes.

Hydrogen oxidation rates were measured in a neutral compost soil and an acidic sandy loam at H2 mixing ratios of 0.01 to 5000 ppmv. The kinetics were biphasic showing two different Km values for H2, one at about 10–40 nM dissolved H2, the other at about 1.2–1.4 μM H2. The low‐Km activity was less sensitive to chloroform fumigation than the high‐Km activity. If sterile soil was amended with Paracoccus denitrificans or a H2‐oxidizing strain isolated from compost soil, it exhibited only a high‐Km (0.7–0.9 μM) activity. It also failed to utilize H2 mixing ratios below a threshold of 1.6–3.0 ppmv H2 (160–300 mPa). A similar result was obtained when fresh soil samples were suspended in water, and H2 oxidation was determined from the decrease of dissolved H2. However, H2 was again utilized to mixing ratios lower than 0.05 ppmv, if the supernatant of the soil suspension or the settled soil particles were dried onto sterile soil or purified quarz sand. Obviously, soils contain two different activities for oxidation of H2: (1) a high‐Km, high‐threshold activity which apparently is due to aerobic H2‐oxidizing bacteria, and (2) a low‐Km, low‐threshold activity whose origin is unknown but presumably is due to soil enzymes.

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The next generation wide-field X-ray telescope (WFXT), to be implemented beyond eRosita and proposed within the NASA RFI call 2011, requires an angular resolution of less than 10 arcsec (with goal of 5") constant across a wide field of view (1 deg 2 ). To achieve this requirement the design is based on nested modified grazing incidence Wolter-I mirrors with polynomial profiles. Our goals in terms of mass and stiffness can be meet with the use of fused silica glass, a wellknown material with good thermo-mechanical properties and polishability characteristics, together with an innovative polishing approach. Here we present the X-ray calibration results obtained for a prototypal shell tested in fullillumination mode at the Panter/MPE facility.