R-Plasmid Transfer in Zymomonas mobilis

Conjugal transfer of three IncP1 plasmids and one IncFII plasmid into strains of the ethanol-producing bacterium Zymomonas mobilis was obtained. These plasmids were transferred at high frequencies from Escherichia coli and Pseudomonas aeruginosa into Z. mobilis and also between different Z. mobilis strains, using the membrane filter mating technique. Most of the plasmids were stably maintained in Z. mobilis, although there was some evidence of delayed marker expression. A low level of chromosomal gene transfer, mediated by plasmid R68.45, was detected between Z. mobilis strains. Genetic evidence suggesting that Z. mobilis may be more closely related to E. coli than to Pseudomonas or Rhizobium is discussed.