@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} } @article {1568, title = {Pollutant degradation by a Methylocystis strain SB2 grown on ethanol: bioremediation via facultative methanotrophy.}, journal = {FEMS Microbiol Lett}, volume = {318}, year = {2011}, month = {2011 May}, pages = {137-42}, abstract = {

A facultative methanotroph, Methylocystis strain SB2, was examined for its ability to degrade chlorinated hydrocarbons when grown on methane or ethanol. Strain SB2 grown on methane degraded vinyl chloride (VC), trans-dichloroethylene (t-DCE), trichloroethylene (TCE), 1,1,1-trichloroethane (1,1,1-TCA), and chloroform (CF), but not dichloromethane (DCM). Growth on methane was reduced in the presence of any chlorinated hydrocarbon. Strain SB2 grown on ethanol degraded VC, t-DCE, and TCE, and 1,1,1-TCA, but not DCM or CF. With the exception of 1,1,1-TCA, the growth of strain SB2 on ethanol was not affected by any individual chlorinated hydrocarbon. No degradation of any chlorinated hydrocarbon was observed when acetylene was added to ethanol-grown cultures, indicating that this degradation was due to particulate methane monooxygenase (pMMO) activity. When mixtures of chlorinated alkanes or alkenes were added to cultures growing on methane or ethanol, chlorinated alkene degradation occurred, but chlorinated alkanes were not, and growth was reduced on both methane and ethanol. Collectively, these data indicate that competitive inhibition of pMMO activity limits methanotrophic growth and pollutant degradation. Facultative methanotrophy may thus be useful to extend the utility of methanotrophs for bioremediation as the use of alternative growth substrates allows for pMMO activity to be focused on pollutant degradation.

}, keywords = {Autotrophic Processes, Biodegradation, Environmental, Environmental Pollutants, Ethanol, Hydrocarbons, Chlorinated, Methane, Methylocystaceae}, issn = {1574-6968}, doi = {10.1111/j.1574-6968.2011.02249.x}, author = {Im, Jeongdae and Semrau, Jeremy D} }