An Unexpectedly Broad Thermal and Salinity-Tolerant Estuarine Methanogen Community

Moderately thermophilic (Tmax, ~55 °C) methanogens are identified after extended enrichments from temperate, tropical and low-temperature environments. However, thermophilic methanogens with higher growth temperatures (Topt ≥ 60 °C) are only reported from high-temperature environments. A microcosm-based approach was used to measure the rate of methane production and methanogen community structure over a range of temperatures and salinities in sediment from a temperate estuary. We report short-term incubations (<48 h) revealing methanogens with optimal activity reaching 70 °C in a temperate estuary sediment (in situ temperature 4–5 °C). While 30 °C enrichments amended with acetate, H2 or methanol selected for corresponding mesophilic trophic groups, at 60 °C, only hydrogenotrophs (genus Methanothermobacter) were observed. Since these methanogens are not known to be active under in situ temperatures, we conclude constant dispersal from high temperature habitats. The likely provenance of the thermophilic methanogens was studied by enrichments covering a range of temperatures and salinities. These enrichments indicated that the estuarine sediment hosted methanogens encompassing the global activity envelope of most cultured species. We suggest that estuaries are fascinating sink and source environments for microbial function study

Absorption Spectra Of Rbcl:Yb Rbbr:Yb And Rbi:Yb Crystals

Single crystals of rubidium chloride, bromide and iodide were doped with substitutional divalent ytterbium, Yb ions, by heating them in ytterbium atmosphere. The absorption spectra of the Yb doped crystals were measured at room and liquid nitrogen temperatures. The spectra were found to consist of intense broad absorption bands located mainly in the ultraviolet spectral region. They have been ascribed to the electric dipole allowed transition of the Yb ions from the 4f(S) ground state to states of the first excited 4f5d configuration of the ions in the crystals. On the basis of the experimental data obtained from the study, an energy level structure has been derived for the 4f5d configuration of Ybions in rubidium chloride, bromide and iodide crystals. Keywords: Rubidium halides, absorption spectra, divalent ytterbium ions and metal vapour phase diffusion.Nigerian Journal of Physics Vol. 19 (2) 2007: pp. 189-20

Ultraviolet absorption spectra of RbBr:Yb2+ crystals at elevated temperatures

No Abstract.GJPAS Vol. 13 (4) 2007: pp. 591-59