Professor Matthysse discusses research into initial interactions of gram-negative bacteria with the plant surface at UNC Department of Biology
Research in my laboratory is centred on the initial interactions of gram-negative bacteria with the plant surface. Most of our studies have focused on two bacterial species, Agrobacterium tumefaciens and Escherichia coli. A. tumefaciens is a soil bacterium. Infections of wound sites of plants with this bacterium result in the formation of crown gall tumours. These tumours result from the transfer of a segment of plasmid DNA (T-DNA) to the plant cell where the DNA is integrated into the host cell chromosomes and expressed. This DNA transfer requires the intimate association of the bacterium with the plant cell surface. The bacteria initially bind loosely to the plant surface. Tighter binding involves the synthesis of bacterial cellulose. The bacteria make glycosidases, some of which are required for tumour formation on some plants. We are currently engaged in cloning characterising the roles of the glycosidase-encoding genes in virulence. Their expression is regulated. We are characterising the compounds which are involved in this regulation and the regulatory pathways. A. tumefaciens is resistant to desiccation and to oxidising agents such as hydrogen peroxide. We are examining the role of extracellular polysaccharides in this resistance and in the interaction with the plant.
E.coli is often only considered in its role as an inhabitant of the intestine and a human pathogen. However, these bacteria when free in the environment often bind to plant surfaces. This binding may aid the bacteria in moving from one host to another. The plant with bound bacteria is consumed by an animal and the bacteria have found a new host. Binding to the plant surface is an active process carried out by the bacteria in response to various signals coming from the plant. Binding may be mediated by many different bacterial surface molecules including proteins and exopolysaccharides and may involve many different mechanisms. This binding is often tight, and the bacteria cannot be removed by water washing. A bacterial biofilm may be formed, and the bacteria may be resistant to treatments which would kill planktonic bacteria. Preventing binding or killing bound bacteria without destroying the quality of the plant as an edible food is the subject of our current research.