| The bacterium Salmonella enterica can use ethanolamine as a sole carbon, nitrogen and energy using a two-step pathway. Given the simple pathway it was surprising to find 17 genes in the operon ( eut) that encodes enzymes for ethanolamine degradation, all of which are expressed only during growth on ethanolamine. Only 5 of the eut genes are required for growth based on genetic analysis, the others had no mutant phenotype. This dissertation reports various conditions under which 10 of the extra genes are needed for growth. The EutH transporter is only required when the uncharged concentration of ethanolamine in the growth medium drops below a critical level. The EutT cobalamin adenosyl transferase is required when CobA adenysyl transferase activity is reduced. The most important group of genes encode EutSMNL and K which are homologous to proteins that form the carboxysome, an organelle needed in some bacteria to concentrate CO2 for fixation during photosynthesis.{09}These genes are needed by Salmonella to conserve a volatile toxic intermediate in the ethanolamine pathway acetaldehyde. The carboxysome is needed whenever growth conditions promote loss of the aldehyde---high pH, rapid diffusion, high temperature. We propose that the carboxysome provides a low pH compartment that conserves acetaldehyde, perhaps as the related acetal. |
