Agrocin 434, a new plasmid encoded agrocin from the biocontrol Agrobacterium strains K84 and K1026, which inhibits biovar 2 agrobacteria

Agrocin 434 is a previously unrecorded inhibitor produced by Agrobacterium strains K84 and K1026, which also secrete agrocin 84. These strains are used for the biological control of crown gall disease of plants and agrocin 434 may contribute to the biocontrol processes. When strain K84 was cured of the plasmids which encode agrocin 84 production (pAgK84) and nopaline catabolism (pAtK84b), the derivative strains retained both agrocin 434 production and the remaining 300-400 kb plasmid. This plasmid was mobilized into a plasmidless recipient and the resulting transconjugants also produced agrocin 434. Processes essential for biosynthesis of agrocin 434 are thus encoded on the large plasmid, for which the designation pAgK434 is recommended. Bioassays of the inhibitory effects of agrocin 434 were done with 68 Agrobacterium isolates from Australia, Europe and North America. All the biovar 2 ( A. rhizogenes) isolates tested were inhibited, with the exception of the strains which produced agrocin 434 themselves. None of the biovar 1 ( A. tumefaciens), biovar 3 ( A. vitis), or A. rubi strains tested was sensitive to agrocin 434. Preliminary chemical analyses indicated that the compound is a di-substituted cytidine nucleoside.