Investigation of the cell surface structures of agrobacteria involved in bacterial and plant interactions

Agrobacterial cells produced straight microfibrils not only when in contact with wheat seedling roots, but also when in contact with each other. After 2 h of incubation, agrobacterial cells were found to form aggregates, in w hich the cells were in contact either directly or through thick straight mi crofibrils (bridges) of an unknown composition. The majority of the microfi brils were susceptible to attack by cellulase, although some of them showed resistance to this enzyme. Like the wild-type flagellated agrobacteria, th eir bald mutants produced long straight microfibrils. The cell surface stru ctures of agrobacteria were examined by labeling them immunocytochemically with colloidal gold-conjugated antibodies against O-specific lipopolysaccha rides, Vir proteins, and cellulase. Agrobacterial cells treated with acetos yringone and brought into contact were found to contain subpolar and polar cell surface structures. Antibodies against the VirB2 protein were able to interact with a tuft of thin microfibrils located on one pole of the agroba cterial cell whose vir genes were induced by acetosyringone but were unable to interact with the surface structures of the agrobacterial cells aggrega ted in liquid medium in the absence of wheat seedlings.