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Plasmid-encoded lysine decarboxylation in Proteus morganii
Abstract:
As a rule, Proteus morganii does not decarboxylate lysine. However, lysine-positive P. morganii strains have been recently described. We suspected a plasmid origin for this atypical character, and we analyzed 14 strains to study this question. Among these strains, 8 yielded lysine-negative segregants after acridine orange or ethidium bromide treatment, and 10 transferred their lysine-positive character to a recipient P. morganii strain. All of the 14 strains analyzed at least segregated or conjugated. Three lysine-positive transconjugants, in turn, segregated lysine-negative variants after ethidium bromide treatment. The eight wild-type lysine-positive strains that segregated lysine-negative subclones contained a large (35 to 45 megadaltons) plasmid detectable by agarose gel electrophoresis. Similarly, the 10 lysine-positive transconjugants contained a plasmid of the same size, whereas P. morganii 1000, the recipient strain, did not contain any detectable plasmid. The large plasmid clearly disappeared in 9 of 11 lysine-negative segregants analyzed. It is concluded that the lysine-positive character of these P. morganii strains is plasmid encoded, and the taxonomical implications are discussed.
Insights
Atypical lysine-positive Proteus morganii strains possess a plasmid encoding this trait. Plasmid loss results in lysine-negative variants, confirming plasmid involvement in this bacterial characteristic.
Area of Science:
- Microbiology
- Bacterial Genetics
- Plasmid Biology
Background:
- Proteus morganii typically does not decarboxylate lysine.
- Recent reports describe lysine-positive P. morganii strains, an unusual phenotype.
- The genetic basis for this atypical lysine decarboxylation was investigated.
Purpose of the Study:
- To determine if the lysine-positive trait in Proteus morganii is plasmid-mediated.
- To analyze the genetic transfer and segregation of the lysine-positive character.
Main Methods:
- Treatment of lysine-positive strains with acridine orange and ethidium bromide to induce segregation.
- Conjugation experiments to transfer the lysine-positive trait to recipient strains.
- Agarose gel electrophoresis to detect and analyze plasmids.
- Segregation analysis of transconjugants.
Main Results:
- Eight of fourteen lysine-positive strains yielded lysine-negative segregants.
- Ten strains successfully transferred the lysine-positive character to a recipient strain.
- Lysine-positive strains and transconjugants harbored a large plasmid (35-45 Mdaltons).
- Loss of this plasmid correlated with the lysine-negative phenotype in segregants.
Conclusions:
- The lysine-positive character in these Proteus morganii strains is encoded by a plasmid.
- Plasmid transfer and segregation confirm its role in the atypical phenotype.
- The findings have implications for the taxonomy and genetic understanding of Proteus morganii.