Pseudomonas for biological control of dutch elm disease. I. Labeling,detection and identification of pseudomonas isolates injected into elms; comparison of various methods

To understand the mechanisms involved in biological control of Dutch elm disease byPseudomonas, data were needed on the distribution of the introduced bacteria within elm and on the development of the bacterial population over a period of time.As traditional biochemical identification techniques are not suitable for distinguishment between individualPseudomonas isolates, three alternative approaches were compared.

1)	Chemotaxonomy, using lipopolysaccharide pattern, cell envelope protein pattern or DNA restriction fragment pattern. These techniques were reliable, but tedious.
2)	Labeling bacteria with a transposon (Tn903) or a plasmid construct (pMON5003) with a metabolic marker (Lac ZY, coding for -galactosidase and lactose permease) allowed for a reliable identification of reisolates. However, populations of transposon-labeled bacteria in elms declined much faster than populations of the unlabeled wild type. The plasmid carrying the metabolic marker disappeared from the bacterial populations over time. Apparently both the transposon and the plasmid were a disadvantage to the bacteria compared with the wild type parent strains.
3)	Immunoagglutination of representative reisolates with an antiserum against theP. fluorescens isolate in use proved to be specific and fast. For routine purposes the immunoagglutination test therefore was the best method of the various ones employed.