@article {1422, title = {Identification and characterization of a NaCl-responsive genetic locus involved in survival during desiccation in Sinorhizobium meliloti.}, journal = {Appl Environ Microbiol}, volume = {79}, year = {2013}, month = {2013 Sep}, pages = {5693-700}, abstract = {

The Rhizobiaceae are a bacterial family of enormous agricultural importance due to the ability of its members to fix atmospheric nitrogen in an intimate relationship with plants. Their survival as naturally occurring soil bacteria in agricultural soils as well as popular seed inocula is affected directly by drought and salinity. Survival after desiccation in the presence of NaCl is enabled by underlying genetic mechanisms in the model organism Sinorhizobium meliloti 1021. Since salt stress parallels a loss in water activity, the identification of NaCl-responsive loci may identify loci involved in survival during desiccation. This approach enabled identification of the loci asnO and ngg by their reduced ability to grow on increased NaCl concentrations, likely due to their inability to produce the osmoprotectant N-acetylglutaminylglutamine (NAGGN). In addition, the mutant harboring ngg::Tn5luxAB was affected in its ability to survive desiccation and responded to osmotic stress. The desiccation sensitivity may have been due to secondary functions of Ngg (N-acetylglutaminylglutamine synthetase)-like cell wall metabolism as suggested by the presence of a d-alanine-d-alanine ligase (dAla-dAla) domain and by sensitivity of the mutant to \β-lactam antibiotics. asnO::Tn5luxAB is expressed during the stationary phase under normal growth conditions. Amino acid sequence similarity to enzymes producing \β-lactam inhibitors and increased resistance to \β-lactam antibiotics may indicate that asnO is involved in the production of a \β-lactam inhibitor.

}, keywords = {Desiccation, DNA Transposable Elements, Gene Expression Regulation, Bacterial, Gene Knockout Techniques, Genes, Bacterial, Genetic Loci, Microbial Viability, Mutagenesis, Insertional, Osmotic Pressure, Sinorhizobium meliloti, Sodium Chloride, Stress, Physiological}, issn = {1098-5336}, doi = {10.1128/AEM.01037-13}, author = {Vriezen, Jan A C and de Bruijn, Frans J and N{\"u}sslein, Klaus} } @article {3148, title = {The Rnf complex of Clostridium ljungdahlii is a proton-translocating ferredoxin:NAD+ oxidoreductase essential for autotrophic growth.}, journal = {mBio}, volume = {4}, year = {2012}, month = {2012 Dec 26}, pages = {e00406-12}, abstract = {

UNLABELLED: It has been predicted that the Rnf complex of Clostridium ljungdahlii is a proton-translocating ferredoxin:NAD(+) oxidoreductase which contributes to ATP synthesis by an H(+)-translocating ATPase under both autotrophic and heterotrophic growth conditions. The recent development of methods for genetic manipulation of C. ljungdahlii made it possible to evaluate the possible role of the Rnf complex in energy conservation. Disruption of the C. ljungdahlii rnf operon inhibited autotrophic growth. ATP synthesis, proton gradient, membrane potential, and proton motive force collapsed in the Rnf-deficient mutant with H(2) as the electron source and CO(2) as the electron acceptor. Heterotrophic growth was hindered in the absence of a functional Rnf complex, as ATP synthesis, proton gradient, and proton motive force were significantly reduced with fructose as the electron donor. Growth of the Rnf-deficient mutant was also inhibited when no source of fixed nitrogen was provided. These results demonstrate that the Rnf complex of C. ljungdahlii is responsible for translocation of protons across the membrane to elicit energy conservation during acetogenesis and is a multifunctional device also implicated in nitrogen fixation.

IMPORTANCE: Mechanisms for energy conservation in the acetogen Clostridium ljungdahlii are of interest because of its potential value as a chassis for the production of biocommodities with novel electron donors such as carbon monoxide, syngas, and electrons derived from electrodes. Characterizing the components implicated in the chemiosmotic ATP synthesis during acetogenesis by C. ljungdahlii is a prerequisite for the development of highly productive strains. The Rnf complex has been considered the prime candidate to be the pump responsible for the formation of an ion gradient coupled with ATP synthesis in multiple acetogens. However, experimental evidence for a proton-pumping Rnf complex has been lacking. This study establishes the C. ljungdahlii Rnf complex as a proton-translocating ferredoxin:NAD(+) oxidoreductase and demonstrates that C. ljungdahlii has the potential of becoming a model organism to study proton translocation, electron transport, and other functions of the Rnf complex in energy conservation or other processes.

}, keywords = {Adenosine Triphosphate, Autotrophic Processes, Clostridium, Energy Metabolism, Fructose, Gene Knockout Techniques, Genes, Essential, Nitrogen, Operon, Oxidoreductases, Proton-Motive Force}, issn = {2150-7511}, doi = {10.1128/mBio.00406-12}, author = {Tremblay, Pier-Luc and Zhang, Tian and Dar, Shabir A and Leang, Ching and Lovley, Derek R} }