Research projects:

Prof. K. Geider, Max-Planck-Institut für Zellbiologie, Ladenburg, Germany.

Molecular characterization and control of the fire blight pathogen Erwinia amylovora

Keywords: Detection, differentiation and molecular genetics of the fireblight pathogen Erwinia amylovora; interaction of bacteria and plant cells; extracellular polysaccharides; bacterial ecology.

Summary: Erwinia amylovora is a Gram-negative bacterium causing fire blight on apple, pear, quince, cotoneaster and other rosaceaous plants. Its pathogenicity mainly depends on its ability to cause a hypersensitive reaction assayed on non-host plants, and on the synthesis of the capsular exopolysaccharide amylovoran for modulation of bacterial interaction with host plants.

Methods: The genetical and biochemical investigations with Erwinia amylovora include transposon mutagenesis, cloning, sequencing and characterization of genes involved in virulence of the bacterium. Signal components from plants, intermediates and degradation products of extracellular polysaccharides (EPS) of the bacteria are assayed by HPLC and enzymatically. An important question is the role of EPS in bacteria/plant interactions. We look for genes involved in EPS biosynthesis and their molecular structural variations and the roles of the gene products. We use reporter genes to determine promoter activities during interaction of the bacteria with host plants. We investigate migration of gfp-labelled E. amylovora in plant tissue, aggressiveness of strains and susceptibility of apple and pear cultivars. Antagonistic principles are assayed for control of the disease. Plant cells were transformed with genes to interfere with colonization of plants by the pathogen. Details and additional references can be found in papers dealing with:

Migration in plants: Bogs, J., Bruchmüller I. & Geider, K. (1998). Colonization of host plants by the fire blight pathogen Erwinia amylovora, marked with genes for bioluminescence and fluorescence. Phytopatholology 88: 416-421.

EPS-synthesis: Bugert, P. & Geider, K. (1995). Molecular analysis of the ams operon required for exopolysaccharide synthesis of Erwinia amylovora. Molecular Microbiology 15: 917-933.

Detection: Bereswill, S., Jock, S., Bellemann, P. & Geider, K. (1998) Identification of Erwinia amylovora by growth in the presence of copper sulfate and by capsule staining with lectin. Plant Disease 82: 158-164.

Fire blight in Europe: Jock, S., Kim, W.-S., Donat, V., Lopez, M. M., Bazzi, C. & Geider, K. (2002): Following spread of fire blight in Western, Central and Southern Europe by molecular differentiation of Erwinia amylovora strains with PFGE analysis. Environmental Microbiology 4: 106-114.