[Show abstract][Hide abstract] ABSTRACT: Salmonellae can use ethanolamine (EA) as a sole source of carbon and nitrogen. This ability is encoded by an operon (eut) containing 17 genes, only 6 of which are required under standard conditions (37 degrees C; pH 7.0). Five of the extra genes (eutM, -N, -L, -K, and -G) become necessary under conditions that favor loss of the volatile intermediate, acetaldehyde, which escapes as a gas during growth on EA and is lost at a higher rate from these mutants. The eutM, -N, -L, and -K genes encode homologues of shell proteins of the carboxysome, an organelle shown (in other organisms) to concentrate CO(2). We propose that carboxysome-like organelles help bacteria conserve certain volatile metabolites-CO(2) or acetaldehyde-perhaps by providing a low-pH compartment. The EutG enzyme converts acetaldehyde to ethanol, which may improve carbon retention by forming acetals; alternatively, EutG may recycle NADH within the carboxysome.
Journal of Bacteriology 05/2006; 188(8):2865-74. · 3.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adenosylcobalamin (Ado-B12) is both the cofactor and inducer of ethanolamine ammonia lyase (EA-lyase), a catabolic enzyme for ethanolamine. De novo synthesis of Ado-B12 by Salmonella enterica occurs only under anaerobic conditions. Therefore, aerobic growth on ethanolamine requires import of Ado-B12 or a precursor (CN-B12 or OH-B12) that can be adenosylated internally. Several known enzymes adenosylate corrinoids. The CobA enzyme transfers adenosine from ATP to a biosynthetic intermediate in de novo B12 synthesis and to imported CN-B12, OH-B12, or Cbi (a B12 precursor). The PduO adenosyl transferase is encoded in an operon (pdu) for cobalamin-dependent propanediol degradation and is induced by propanediol. Evidence is presented here that a third transferase (EutT) is encoded within the operon for ethanolamine utilization (eut). Surprisingly, these three transferases share no apparent sequence similarity. CobA produces sufficient Ado-B12 to initiate eut operon induction and to serve as a cofactor for EA-lyase when B12 levels are high. Once the eut operon is induced, the EutT transferase supplies more Ado-B12 during the period of high demand. Another protein encoded in the operon (EutA) protects EA-lyase from inhibition by CN-B12 but does so without adenosylation of this corrinoid.
Journal of Bacteriology 12/2004; 186(22):7635-44. · 3.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The eutH gene is part of an operon that allows Salmonella enterica to use ethanolamine as a sole source of nitrogen, carbon, and energy. Although the sequence of EutH suggests a role in transport, eutH mutants use ethanolamine normally under standard conditions (pH 7.0). These mutants fail to use ethanolamine at a low pH. Evidence is presented that protonated ethanolamine (Eth0) does not enter cells, while uncharged ethanolamine (Eth0) diffuses freely across the membrane. The external concentration of Eth0 varies with the pH (pK=9.5). At pH 7.0, the standard ethanolamine concentration (41 mM) provides enough Eth0 for an influx rate that can support growth with or without EutH. When a lowered pH and/or ethanolamine concentration reduced the Eth0 concentration below 25 microM, EutH was needed to facilitate diffusion. EutH+ cells grew normally at Eth0 concentrations above 3 microM, close to the Km (9 microM) of the first degradative enzyme, ethanolamine ammonia lyase. It is suggested that EutH facilitates diffusion of Eth0. As predicted for a transporter, EutH contributed to the toxicity of ethanolamine seen under some conditions; furthermore, fusion of EutH to fluorescent Yfp protein provided evidence that EutH is a membrane protein.
Journal of Bacteriology 11/2004; 186(20):6885-90. · 3.19 Impact Factor