Does Composition of the Exopolysaccharide Matrix of Pseudomonas Putida Control Biofilm Architecture and Fitness In Low-water-content Environments?

Iowa State University, Ames IA

Investigators

Abstract

Intellectual Merit: Bacteria in soil and other unsaturated habitats, such as lungs or aerial surfaces of plants, generally live as aggregates of cells (biofilms) within a matrix comprised, in part, of extracellular polysaccharides (EPS) of their own making. Although there is general agreement that bacteria in many environments, including aquatic biofilm communities, live within an EPS matrix, relatively little is known about the function of the EPS layer in general or even specific polysaccharide components of the matrix. One possibility that has been often discussed but has been the subject of relatively few studies is that an EPS envelope may protect bacteria from drying, thus functioning as a fitness trait in low water content habitats. Soil microorganisms mediate many critical terrestrial ecosystem processes, including global biogeochemical cycles, the degradation of organic pollutants, and beneficial and detrimental interactions with plants, yet we still have a poor understanding of how water availability influences biofilm development and metabolic activities and the survival of community members. The goal of this project is to understand the processes involved in bacterial colonization of soil and how the environment influences bacterial fitness, including the mechanisms by which environmental cues are integrated into the regulatory networks involved in adaptation to those stresses. The central hypothesis that serves as a framework for this project is that the availability of water to bacteria is a major force influencing bacterial physiology, growth, and survival. The hypotheses that will be tested are that modulation of the composition of the EPS matrix is an active process that is driven by dehydration stress and that specific EPS constituents hold substantial amounts of water thereby creating a microenvironment that slows the rate of biofilm drying, which increases bacterial survival by increasing the time for metabolic adjustment. Furthermore, stress-mediated modulation of the EPS matrix alters biofilm developmental processes and architecture, which ultimately influences the biophysical properties of the biofilm and the metabolic capabilities of community members. The objectives of the project are to: 1, identify genes involved in extracellular polysaccharide biosynthesis, assess their regulation and inactivate them; 2, assess whether extracellular polysaccharides create a more hydrated microenvironment that protects biofilm cells from desiccation stress; and 3, assess the role of EPS on biofilm developmental patterns and architecture in low water content habitats. Broader impacts: An important component of this research is to fill a major gap in our understanding of biofilm biology in terrestrial ecosystems, which has had to typically rely on information obtained from experimental systems that frequently don't reflect soil conditions. This project will provide multiple opportunities for research training coupled to instruction and to promote inquiry based learning strategies. Students will be challenged to identify linkages of this project to regulatory hierarchies and signal transduction pathways and to the broader implications of these growth forms on terrestrial ecosystem processes. Information will be disseminated through publications and presentations at meetings and through a website that will contain images and descriptions of unsaturated biofilm development and properties that are not available in publication format. Furthermore, the results and experimental methodologies will be incorporated into the undergraduate microbiology curriculum into new lecture and laboratory courses the PI is currently developing.