Acquisition of aspartase activity in Rhizobium leguminosarum WU235
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Rhizobium leguminosarum WU235 expresses aspartase (EC 126.96.36.199) when grown on aspartate or asparagine as the sole carbon source, but not on glucose or fumarate. Cells grown on glucose plus aspartate, or fumarate plus aspartate, do not express aspartase. Although these results are reminiscent of catabolite control of an inducible enzyme, induction of aspartate cannot be demonstrated in this strain. Aspartase-producing cells synthesize the enzyme after repeated subculture on glucose plus NH4Cl. Cell grown in glucose plus NH4Cl and plated onto aspartate produce different colony sizes; the larger (0.1% of the total) express aspartate, while the smaller do not. At dilutions sufficient to exclude the large aspartate-producing colonies, a single-sized, aspartase-negative colony was found initially. Such colonies later developed papillae or became cluster colonies; aspartate was produced with papillae formation. The aspartate producing strains were shown, by analysis of native plasmids and periplasmic proteins and by the use of antibiotic resistant strains, to be derived from the parental type. The data suggest that strain WU235 is unable to produce aspartate unless a mutation occurs which leads to constitutive enzyme synthesis. The significance of these observations for studies claiming catabolite repression in Rhizobium is discussed.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Environmental and Life Sciences|
|Publisher:||Society for General Microbiology|
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