Our data suggest that high-dose RSV supplementation positively affects bone, primarily by stimulating formation or mineralization. Future studies of longer duration comprising populations at risk of osteoporosis are needed to confirm these results.

Summary Filamentous sulphide‐oxidizing Beggiatoa spp. often occur in large numbers in the coastal seabed without forming visible mats on the sediment surface. We studied the diversity, population structure and the nitrate‐storing capability of such bacteria in the Danish Limfjorden and the German Wadden Sea. Their distribution was compared to the vertical gradients of O2, NO3– and H2S as measured by microsensors. The main Beggiatoa spp. populations occurred in a 0.5–3 cm thick intermediate zone, below the depth of oxygen and nitrate penetration but above the zone of free sulphide. The Beggiatoa spp. filaments were found to store nitrate, presumably in liquid vacuoles up to a concentration of 370 mM NO3–, similar to the related large marine sulphur bacteria, Thioploca and Thiomargarita. The observations indicate that marine Beggiatoa spp. can live anaerobically and conserve energy by coupling sulphide oxidation with the reduction of nitrate to dinitrogen and/or ammonia. Calculations of the diffusive nitrate flux and the potential sulphide oxidation by Beggiatoa spp. show that the bacteria may play a critical role for the sulphur cycling and the nitrogen balance in these coastal environments. 16S rDNA sequence analysis shows a large diversity of these uncultured, nitrate‐storing Beggiatoa spp. Smaller (9–17 µm wide) and larger (33–40 µm wide) Beggiatoa spp. represent novel phylogenetic clusters distinct from previously sequenced, large marine Beggiatoa spp. and Thioploca spp. Fluorescence in situ hybridization (FISH) of the natural Beggiatoa spp. populations showed that filament width is a conservative character of each phylogenetic species but a given filament width may represent multiple phylogenetic species in a mixed population.

No abstract

A biosensor for NO(3)(-) containing immobilized dentrifying bacteria and a reservoir of liquid growth medium for the bacteria was constructed. The bacteria did not have a N(2)O reductase and therefore reduced NO(3)(-) to N(2)O, which was then subsequently quantified by a built-in electrochemical transducer for N(2)O. The only agents interfering with the determination of NO(3)(-) were NO(2)(-) and N(2)O. The sensitivity for NO(2)(-) was identical to the one for NO(3)(-) whereas the sensitivity for N(2)O was 2.4 times higher than for NO(3)(-). Diffusive supply of electron donors to the bacteria from the built-in reservoir of growth medium ensured that the biosensor could work for 2-4 days. The tip diameter was down to 20 μm, and the sensors exhibited perfectly linear responses to nitrate in both freshwater and seawater. The detection limit was ∼1 μM. The 90% response time to changes in NO(3)(-) concentration was from 15 to 60 s at room temperature and about twice that at 6 °C, which was the lowest temperature for successful operation. The new NO(3)(-) biosensor is a very useful tool for the study of nitrogen metabolism in nature.

Microsensors, including a recently developed NO 3؊ biosensor, were applied to measure O 2 and NO 3 ؊ profiles in marine sediments from the upwelling area off central Chile and to investigate the influence of Thioploca spp. on the sedimentary nitrogen metabolism. The studies were performed in undisturbed sediment cores incubated in a small laboratory flume to simulate the environmental conditions of low O 2 , high NO 3 ؊ , and bottom water current. On addition of NO 3 ؊ and NO 2 ؊ , Thioploca spp. exhibited positive chemotaxis and stretched out of the sediment into the flume water. In a core densely populated with Thioploca, the penetration depth of NO 3 ؊ was only 0.5 mm and a sharp maximum of NO 3 ؊ uptake was observed 0.5 mm above the sediment surface. In sediments with only few Thioploca spp., NO 3 ؊ was detectable down to a depth of 2 mm and the maximum consumption rates were observed within the sediment. No chemotaxis toward nitrous oxide (N 2 O) was observed, which is consistent with the observation that Thioploca does not denitrify but reduces intracellular NO 3 ؊ to NH 4 ؉ . Measurements of the intracellular NO 3 ؊ and S 0 pools in Thioploca filaments from various depths in the sediment gave insights into possible differences in the migration behavior between the different species. Living filaments containing significant amounts of intracellular NO 3 ؊ were found to a depth of at least 13 cm, providing final proof for the vertical shuttling of Thioploca spp. and nitrate transport into the sediment.