Extremophilic organisms require specialized enzymes for their exotic metabolisms. Acid-loving thermophilic Archaea that live in the mudpots of volcanic solfataras obtain their energy from reduced sulphur compounds such as hydrogen sulphide (H(2)S) and carbon disulphide (CS(2)). The oxidation of these compounds into sulphuric acid creates the extremely acidic environment that characterizes solfataras. The hyperthermophilic Acidianus strain A1-3, which was isolated from the fumarolic, ancient sauna building at the Solfatara volcano (Naples, Italy), was shown to rapidly convert CS(2) into H(2)S and carbon dioxide (CO(2)), but nothing has been known about the modes of action and the evolution of the enzyme(s) involved. Here we describe the structure, the proposed mechanism and evolution of a CS(2) hydrolase from Acidianus A1-3. The enzyme monomer displays a typical β-carbonic anhydrase fold and active site, yet CO(2) is not one of its substrates. Owing to large carboxy- and amino-terminal arms, an unusual hexadecameric catenane oligomer has evolved. This structure results in the blocking of the entrance to the active site that is found in canonical β-carbonic anhydrases and the formation of a single 15-Å-long, highly hydrophobic tunnel that functions as a specificity filter. The tunnel determines the enzyme's substrate specificity for CS(2), which is hydrophobic. The transposon sequences that surround the gene encoding this CS(2) hydrolase point to horizontal gene transfer as a mechanism for its acquisition during evolution. Our results show how the ancient β-carbonic anhydrase, which is central to global carbon metabolism, was transformed by divergent evolution into a crucial enzyme in CS(2) metabolism.

Yeast strains (157) belonging to at least 9 genera were isolated from natural habitats and screened for killer-sensitive relationships. Killer and sensitive characteristics were exhibited by 17 and 11% of the isolates, respectively. The strains belong to either one of two mutually exclusive killer-sensitive groups.

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Production of the killer toxin of Pichia kluyveri 1002 was stimulated in the presence of yeast extract. In a minimal medium production was optimal at pH 3.8-4.0 and 22--25 degrees C. Addition of gelatin and nonionic detergents, like Brij-58 (polyoxyethylene 20 cetyl ether) and Triton-X-100, to this medium enhanced production significantly. The killer toxin was purified 140-fold by use of a stepwise ethanol precipitation and butyl Sepharose column chromatography. The purified killer toxin, which still contained some carbohydrates, appeared to be glycoprotein with a mol wt of about 19 000 and an isoelectric point of 4.3. It was stable between pH 2.5 and 4.7 and up to 40 degrees C.

Skeletal Mg/Ca ratios of well-preserved fossil echinoderms have been used to reconstruct past Mg/Ca ratio in seawater up to the Phanerozoic, taking into account the known temperature effect on this ratio. This study investigates the effects of salinity and growth rate on Mg/Ca and Sr/Ca ratios in starfi sh calcite skeletons grown in experimental conditions. Both ratios are not related to growth rate: on the contrary, both are positively related to salinity. This effect induces an error on the reconstructed Mg/Ca ratio in seawater that may reach 46%. An intriguing inverse relation between skeletal Sr/Ca ratio and temperature was recorded. The salinity effects are presumably due to physiological regulation processes.