Muscle-specific mutations accumulate with aging in critical human mtDNA control sites for replication.

The recently discovered aging-dependent large accumulation of point mutations in the human fibroblast mtDNA control region raised the question of their occurrence in postmitotic tissues. In the present work, analysis of biopsied or autopsied human skeletal muscle revealed the absence or only minimal presence of those mutations. By contrast, surprisingly, most of 26 individuals 53 to 92 years old, without a known history of neuromuscular disease, exhibited at mtDNA replication control sites in muscle an accumulation of two new point mutations, i.e., A189G and T408A, which were absent or marginally present in 19 individuals younger than 34 years. These two mutations were not found in fibroblasts from 22 subjects 64 to 101 years of age (T408A), or were present only in three subjects in very low amounts (A189G). Furthermore, in several older individuals exhibiting an accumulation in muscle of one or both of these mutations, they were nearly absent in other tissues, whereas the most frequent fibroblast-specific mutation (T414G) was present in skin, but not in muscle. Among eight additional individuals exhibiting partial denervation of their biopsied muscle, four subjects >80 years old had accumulated the two muscle-specific point mutations, which were, conversely, present at only very low levels in four subjects <or =40 years old. The striking tissue specificity of the muscle mtDNA mutations detected here and their mapping at critical sites for mtDNA replication strongly point to the involvement of a specific mutagenic machinery and to the functional relevance of these mutations.

A transposase-independent mechanism gives rise to precise excision of IS256 from insertion sites in Staphylococcus epidermidis.

The mobile element IS256 causes phase variation of biofilm formation in Staphylococcus epidermidis by insertion and precise excision from the icaADBC operon. Precise excision, i.e., removal of the target site duplications (TSDs) and restoration of the original DNA sequence, occurs rarely but independently of functional transposase. Instead, the integrity of the TSDs is crucial for precise excision. Excision increased significantly when the TSDs were brought into closer spatial proximity, suggesting that excision is a host-driven process that might involve most likely illegitimate recombination.

Molecular characterization of Nosema bombi (Microsporidia : Nosematidae) and a note on its sites of infection in Bombus terrestris (Hymenoptera : Apoidea)

Investigations of queen, worker and male bumble bees (Bombus terrestris) showed that all individuals became infected with Nosema bombi. Infections were found in Malpighian tubules, thorax muscles, fat body tissue and nerve tissue, including the brain. Ultrastructural studies revealed thin walled emptied spores in host cell cytoplasm interpreted as autoinfective spores, besides normal spores (environmental spores) intended for parasite transmission between hosts. The nucleotide sequence of the gene coding for the small subunit rRNA (SSU-rRNA) from Microsporidia isolated from B. terrestris, B. lucorum, and B. hortorum were identical, providing evidence that N. bombi infects multiple hosts. The sequence presented here (GenBank Accession no AY008373) is different from an earlier submission to GenBank (Accession no U26158) of a partial sequence of the same gene based on material collected from B. terrestris. It still remains to be investigated if there is species diversity among Microsporidia found in bumble bees.

CO multipulse TAP studies of 2% Pt/CeO2 catalyst: Influence of catalyst pretreatment and temperature on the number of active sites observed

CO multipulse temporal analysis of products (TAP) experiments were used to characterize a ceria-supported platinum catalyst after various oxidative and reductive pretreatments using O-2, H2O, CO2, and H-2. Based on the amount of CO consumed, using the final CO-saturated catalyst composition as the common state point, the oxidatively pretreated catalyst could be described using a general scale. From a kinetic analysis of the CO multipulse responses, two kinetic regimes corresponding to two types of active sites could be identified. As the temperature was raised, the number of the most active sites did not change while the amount of the less active site increased. Comparison of the number of active sites determined from the TAP data reported herein with that determined by a previous steady-state isotope transient kinetic analysis experiment showed excellent agreement. This correlation indicates that the (very fast response) TAP experiments can provide information regarding the number and type of active sites that are relevant to a catalyst under real reaction conditions. (c) 2007 Elsevier Inc. All rights reserved.

Low-temperature catalytic decomposition of N2O on platinum and bismuth-modified platinum: identification of active sites

Classification of the active surface sites of platinum catalysts responsible for low temperature N2O decomposition, in terms of steps, kinks and terraces, has been achieved by controlled addition of bismuth to as-received platinum/graphite catalysts.