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ATP/ADP Translocases: a Common Feature of Obligate Intracellular Amoebal Symbionts Related to Chlamydiae and Rickettsiae. Stephan Schmitz-Esser, 2004.ATP/ADP translocases catalyze the highly specific transport of ATP across a membrane in an exchange mode with ADP . Such unique transport proteins are employed by plant plastids and have among the prokaryotes so far only been identified in few obligate intracellular bacteria belonging to the Chlamydiales and the Rickettsiales . In this study, 12 phylogenetically diverse bacterial endosymbionts of free-living amoebae and paramecia were screened for the presence of genes encoding ATP/ADP transport proteins . The occurrence of ATP/ADP translocase genes was found to be restricted to endosymbionts related to rickettsiae and chlamydiae . We showed that the ATP/ADP transport protein of the Parachlamydia-related endosymbiont of Acanthamoeba sp . strain UWE25, a recently identified relative of the important human pathogens Chlamydia trachomatis and Chlamydophila pneumoniae, is functional when expressed in the heterologous host Escherichia coli and demonstrated the presence of transcripts during the chlamydial developmental cycle . These findings indicate that the interaction between Parachlamydia-related endosymbionts and their amoeba hosts concerns energy parasitism similar to the interaction between pathogenic chlamydiae and their human host cells . Phylogenetic analysis of all known ATP/ADP translocases indicated that the genes encoding ATP/ADP translocases originated from a chlamydial ancestor and were, after an ancient gene duplication, transferred horizontally to rickettsiae and plants . The Single Superoxide Dismutase of Rhodobacter capsulatus Is a Cambialistic, Manganese-Containing Enzyme. Leandro C. Tabares, 2003.The phototrophic bacterium Rhodobacter capsulatus contains a single, oxygen-responsive superoxide dismutase (SODRc) homologous to iron-containing superoxide dismutase enzymes . Recombinant SODRc, however, displayed higher activity after refolding with Mn2+, especially when the pH of the assay mixture was raised . SODRc isolated from Rhodobacter cells also preferentially contains manganese, but metal discrimination depends on the culture conditions, with iron fractions increasing from 7% in aerobic cultures up to 40% in photosynthetic cultures . Therefore, SODRc behaves as a Mn-containing dismutase with cambialistic properties . Abundance of Reverse Tricarboxylic Acid Cycle Genes in Free-Living Microorganisms at Deep-Sea Hydrothermal Vents. Barbara J. Campbell, 2004.Since the discovery of hydrothermal vents more than 25 years ago, the Calvin-Bassham-Benson (Calvin) cycle has been considered the principal carbon fixation pathway in this microbe-based ecosystem . However, on the basis of recent molecular data of cultured free-living and noncultured episymbiotic members of the epsilon subdivision of Proteobacteria and earlier carbon isotope data of primary consumers, an alternative autotrophic pathway may predominate . Here, genetic and culture-based approaches demonstrated the abundance of reverse tricarboxylic acid cycle genes compared to the abundance of Calvin cycle genes in microbial communities from two geographically distinct deep-sea hydrothermal vents . PCR with degenerate primers for three key genes in the reverse tricarboxylic acid cycle and form I and form II of ribulose 1,5-bisphosphate carboxylase/oxygenase (Calvin cycle marker gene) were utilized to demonstrate the abundance of the reverse tricarboxylic acid cycle genes in diverse vent samples . These genes were also expressed in at least one chimney sample . Diversity, similarity matrix, and phylogenetic analyses of cloned samples and amplified gene products from autotrophic enrichment cultures suggest that the majority of autotrophs that utilize the reverse tricarboxylic acid cycle are members of the epsilon subdivision of Proteobacteria . These results parallel the results of previously published molecular surveys of 16S rRNA genes, demonstrating the dominance of members of the epsilon subdivision of Proteobacteria in free-living hydrothermal vent communities . Members of the epsilon subdivision of Proteobacteria are also ubiquitous in many other microaerophilic to anaerobic sulfidic environments, such as the deep subsurface . Therefore, the reverse tricarboxylic acid cycle may be a major autotrophic pathway in these environments and significantly contribute to global autotrophic processes . Salmonella enterica Serovar Typhimurium and Listeria monocytogenes Acid Tolerance Response Induced by Organic Acids at 20°C: Optimization and Modeling. E. J. Greenacre, 2003.An acid tolerance response (ATR) has been demonstrated in Listeria monocytogenes and Salmonella enterica serovar Typhimurium in response to low pH poised (i.e., adapted) with acetic or lactic acids at 20°C and modeled by using dynamic differential equations . The ATR was not immediate or prolonged, and optimization occurred after exposure of L . monocytogenes for 3 h at pH 5.5 poised with acetic acid and for 2 h at pH 5.5 poised with lactic acid and after exposure of S . enterica serovar Typhimurium for 2 h at pH 5.5 poised with acetic acid and for 3 h at pH 5.5 poised with lactic acid . An objective mechanistic analysis of the acid inactivation data yielded estimates of the duration of the shoulder (ts), the log-linear decline (kmax), and the magnitude of a critical component (C) . The magnitude of kmax gave the best agreement with estimates of conditions for optimum ATR induction made from the raw data .
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