Working Group: Bacteriology

Section: Bacteria

Plant pathogenic bacteria cause annually major crop losses world-wide. The rapid development of sequencing technologies allowed not only an improved and fast 16S rRNA gene based identification of plant pathogenic bacteria but also sequencing of complete genomes for many plant pathogenic bacteria. Thus important new insights into the diversity and evolution of plant pathogenic bacteria, the mechanisms of pathogen attack but also the response of the plants to the pathogen attack were recently gained. However, still little is known of the ecology of most plant pathogenic bacteria. A major focus of the research is the development and use of cultivation-independent methods to detect and quantify the abundance of plant pathogenic bacteria in environmental samples in order to elucidate their ecology in the context of indigenous microbial communities. Furthermore, we are interested in studying the contribution of mobile genetic elements in pathogenicity and host range.

Epidemiology

The abundance and diversification of plant pathogenic bacteria in soil or plant material might be influenced by changes in climate or agricultural practice (GM crops, no till versus tillage).  In order to better understand the ecology and dissemination of plant pathogenic bacteria molecular methods are being used. Our studies aim to elucidate the biotic and abiotic factors influencing the structural and functional composition of indigenous microbial communities, the abundance and diversification of plant pathogenic bacteria.
Major research topics are:

• Genetic diversity of plant pathogenic bacteria studied by molecular fingerprinting techniques to elucidate the factors shaping their diversity
• Cultivation-independent quantification of pathogens or pathogenicity determinants
• Role of mobile genetic elements in diversification, pathogenicity and host range.

Diagnostics

A prerequisite for an early and reliable detection of plant pathogenic bacteria is the development of sensitive and specific detection methods. The increasing number of completely sequenced bacterial pathogens and improved understanding of major pathogenicity determinants greatly facilitates the development of diagnostic tools. This requires:

• The development of quantitative PCR systems for the cultivation-independent quantification of plant pathogenic bacteria
• Use of different detection techniques to detect plant pathogenic bacteria in plant material, soil or irrigation water.

Current research topics

• Development and targeted adjustment of methods to detect bacterial pathogens 
• Development of cultivation-independent methods to detect and quantify bacterial plant pathogens in total community DNA directly extracted from soils, irrigation water and plant material (seeds, leaves, stem, roots) (collaboration partner: Dr. R. Ries, Geisenheim)
• Genetic flexibility of phytopathogenic bacteria by means of plasmid-mediated pathogenicity factors (collaboration partner: Prof. Wohanka, Geisenheim)
• Epidemiology and biocontrol of Ralstonia solanacearum (collaboration with Prof. Jian-Hua Guo, Nanjing Agricultural University): Unravel the complex interaction of plant pathogens, antagonists and indigenous microbial communities in dependence of soil type, plant species, cultivar and agricultural practice
• Direct and indirect risks for humans and animals from plant-associated bacteria (e.g., transferable antibiotic resistances)
• Preservation and extension of the reference collection of plant-associated bacteria (pathogens and antagonists) as a basis for the development of methods.