Abstract
The criteria generally used in the classification of
the genus Agrobacterium and the genus Rhizobium have been
evaluated and found to be unsuitable for both differentiation of
the genera and the species. Other tests based on the types of
reaction expected to occur in the plant have been examined.
No in vitro method was found to differentiate the saprophytic
Agrobacterium radiobacter from the pathogenic form, A.tumefaciens,
but it is suggested that tests based on organic nitrogen
metabolizm can be used to differentiate both genera. A selective
medium has been developed for agrobacteria which is also useful
in distinguishing between agrobacteria and rhizobia. The reactions
leading to the production of 3- ketolactose from lactose by some
agrobacteria have been examined. It is shown that the production
is temperature dependent and phosphate sensitive. The reasons
why certain strains of agrobacteria do not form 3- ketolactose
have been determined. All attempts to induce such strains to
form excess 3- ketolactose, and so achieve uniformity within the
genus, failed. It was suggested that this reducing sugar
intermediate may aid in the survival of the pathogen in the host
plant, and a detailed examination was made of this suggestion in
relation to the effects of temperature on gall initiation. Phenols
appeared to be essential in plant defence against bacterial
invasion. The resistance of the plant might be increased or
decreased depending on whether the phenol systems were augmented
or inhibited. The phenols seemed to have a dual role, as indole
acetic acid synergists or inhibitors, and an examination of their
effect on destruction of IAA and on peroxidase reactions showed
that plant "indole acetic acid oxidase" is probably associated
with peroxidation.
