CAREER: Biofilm Formation and Biological Control in Pseudomonas

Dartmouth College, Hanover NH

Investigators

Abstract

The formation of bacterial biofilms, or surface attached communities, is important in agricultural, industrial, and medical settings. It has become increasingly clear in the past 2 decades that in most natural environments bacteria are found predominately attached to surfaces, such as soil particles or plant roots. When found in association with plant roots, certain bacterial strains such as fluorescent Pseudomonads can protect plants from pathogens in the soil in a process known as biological control and do so in a cost-effective and environmentally friendly manner. Bacteria living in the rhizosphere can occupy three niches: i) as a biofilm on soil (abiotic surfaces), ii) as a biofilm on plants (biotic surfaces), and/or iii) as planktonic (free-swimming) cells. It is not known how the ability to interact with biotic and abiotic surfaces, and to transition between a planktonic and attached life style, affects protection of plants and survival of the bacteria. These are important issues for effective biological control strategies. The role of biofilm formation in bacterial colonization of plant roots (a process thought to contribute to biological control) and biological control is also not well understood. Surface attachment defective (sad) mutants of Pseudomonas fluorescens WCS365, a biological control strain, have been isolated which are defective for biofilm formation on an abiotic (plastic) surface. The goal of this research project is to gain a better understanding of the role of genes required for biofilm formation in biological control, root colonization, attachment to soil, and bacterial survival. To accomplish this goal,extensive phenotypic characterization of the sad mutants will be carried out. The mechanistic role that the product of the sad-18 gene plays in biofilm formation, biological control, and survival in the soil will be explored in detail to complement the phenotypic studies. Finally, the conservation of these sad genes in other fluorescent Pseudomonads will also be addressed. The long term goal of this research is to better understand how natural isolates of bacteria can protect plants from disease-causing organisms. This bacterial-based protection of plants is known as biological control. The traditional methods to protect plants from disease or damage includes the extensive use of pesticides, herbicides, and fungicides. This is a quite expensive process (costing billion of dollars annually) and presents a very real threat to the environment, drinking water supplies, and the health of farm workers. Therefore, developing alternative means to protect agriculturally important plants by using more natural or organic approaches, such as biological control, is a very important area of research.