Conjugative transfer of plasmid pTd33 in agrobacteria

Supramembrane structures that connect conjugating agrobacterial cells were visualized for the first time by transmission electron microscopy. The prim ary contact of cells during conjugation was shown to occur through the form ation of long pill containing no VirB1 protein. Pretreatment of agrobacteri al cells with acetosyringone resulted in a six- to tenfold increase in the transfer frequency of plasmid pTd33 at 19-25 degrees C and had almost no ef fect at 30 degrees C. The transfer of plasmid pTd33 from A. tumefaciens str ain GV3101 to plasmid-free A. tumefaciens strain UBAPF-2 was 16 times decre ased after the centrifugation of cells. The transfer efficiency of plasmid pTd33 from A. tumefaciens strain LBA2525 (virB2::lacZ) to plasmid-free A. t umefaciens strain UBAPF-2 was one order of magnitude lower than the transfe r from the wild-type A. tumefaciens strain GV3101. Treatment of donor cells with 0.01% SDS before mating decreased the transfer efficiency by a factor of 26. The role of pill in the establishment of contact between conjugatin g cells of agrobacteria is discussed.