Studies on inhibitory compounds produced by Agrobacterium radiobacter strain 84 Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w3763958f

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  • A study was made of compounds produced by Agrobacterium radiobacter strain 84 that are inhibitory to some pathogenic strains of A. tumefaciens. Agrocins (inhibitory compounds) were partially purified from large volumes of A. radiobacter strain 84 culture supernatants to determine (i) if more than one agrocin is produced, (ii) if partially purified agrocin prevents crown gall disease on tomatoes, and (iii) the mechanism of action of agrocin. The agrocin(s) were partially purified by DEAE cellulose chromatography, acetone precipitation, P-4 gel filtration, and high performance liquid chromatography (HPLC). These procedures resulted in two fractions (I and II) that were inhibitory when tested against the pathogen, A. tumefaciens K-24. When fraction II was subjected to high salt gel filtration chromatography, it separated into two active fractions (IIa and IIb). When fraction I was subjected to HPLC chromatography, it failed to elute from the column. These data suggest fraction I is of a different chemical nature than fractions IIa and IIb. The three fractions described above were used to screen selected strains of Agrobacterium for sensitivity. The majority of the strains tested were sensitive to fraction I, but not fractions IIa and IIb. Only a small number of strains proved to be sensitive to all three fractions, and those strains sensitive to fraction IIa were also sensitive to fraction lib. Of interest is A. tumefaciens C58, which is sensitive to all three fractions, but when cured of its tumor inducing (Ti) plasmid is only sensitive to fraction I. This suggests sensitivity to fractions IIa and IIb is coded for by the Ti plasmid and fraction I by the host chromosome, or another plasmid within the sensitive bacterium. Partially purified agrocin applied to wounds decreased the incidence of galling by A. tumefaciens K24 on tomato seedlings in the greenhouse. Maximum inhibition occurred after five hours and resulted in 11% galled plants for the agrocin treated plants versus 100% galled plants for the untreated control. These experiments suggest that the agrocin(s) produced by A. radiobacter strain 84 are at least in part responsible for its antagonistic nature. Further studies will be necessary to elucidate the chemical structures of the agrocins and to determine the mechanism by which strain 84 inhibits sensitive strains of Agrobacterium.
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