Plasmid-encoded lysine decarboxylation in Proteus morganii

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.