Four different plasmids were electro transformed into Zymomonas mobilis ZM4 and CP4, two important ethanol-producing strains. The results showed that the best source strain for preparing plasmids was the transformed host strain itself, and Escherichia coli JM110 as the source strain could yield significantly higher transformation efficiencies than Top10. The optimal recovery time of transformed ZM4 or CP4 cells to obtain maximum number of transformants and highest transformation efficiency was 11 h for pZB21-mini, pZB21 and pZA22, but 24 or 20 h for pBBR1MCS-2. The optimal electric field strength for pZB21-mini was 13.25 kV /cm in ZM4 and 14.0 kV /cm in CP4.But for pZA22 and pBBR1MCS-2, it was 11.75 kV /cm in ZM4 and 12.5 kV /cm in CP4; for pZB21, also 12.5 kV /cm in CP4.These plasmids were shown to be more stable in ZM4 than in CP4 by serial transfer to antibiotic-free medium and the 3 plasmids were more stable than pBBR1MCS-2. The results will help to support the genetic and biotechnological research of Z. mobilis by providing information about some of the most important factors that influence the transformation of ZM4 and CP4, and also providing insights into the similarities and differences in their restriction-modification (R-M) systems.
Key words: Zymomonas mobilis, plasmids, electroporation, transformation, plasmid stability
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