Center for Biofilm Engineering

Thesis Abstract:  

"Structure and Activity of Pseudomonas aeruginosa PAO1 Biofilms" 

Mathematical models of biofilms play a vital part in understanding biofilm processes in the environment and in the industry. Modeling has evolved from using the simplest conceptual models of homogenous to the heterogeneous biofilms and to the stratified biofilms. Most models predict nutrient concentration profiles in the biofilms. However, since these models are based on assumptions about biofilm structure and activity, the predictions are valid only within the domain determined by these assumptions. If the assumptions reflect the conditions in actual biofilms accurately, then the models can realistically predict the behavior of a real biofilm. Nutrient concentration profiles are affected by the mass transport outside the biofilm, inside the biofilm, and by the structure of the biofilm. To understand the distribution of biofilm activity, it is necessary to correlate the local nutrient concentration, local mass transport in the biofilm and the biofilm structure. This study shows the correlations among surface averaged dissolved oxygen concentration, surface averaged relative effective diffusivity, and areal porosity in the biofilms of Pseudomonas aeruginosa PAO1 grown in a flat plate reactor, under the framework of Stratified Biofilms concept. Three dimensional distributions of local dissolved oxygen concentration, local relative effective diffusivity, and porosity in the biofilm were measured. It was found that the local dissolved oxygen concentrations and relative effective diffusivities correlate weakly with each other or with the areal porosity. However surface averaged dissolved oxygen concentration and surface averaged relative effective diffusivity strongly correlated with each other and with the areal porosity. In this study, surface averaged dissolved oxygen concentration, surface averaged relative effective diffusivity, and areal porosity decreased towards the bottom of the biofilm, while the coefficients of variation computed for each of these parameters increased towards the bottom of the biofilm. The coefficient of variation is a measure of the heterogeneity of the biofilm. The increase in the coefficient of variation shows that the heterogeneity of the biofilm increases towards the bottom of the biofilm.

Structure and Activity of Pseudomonas aeruginosa PAO1 Biofilms, Thesis Defense by Raaja Raajan Angathevar Veluchamy, M.S. Candidate in Chemical and Biological Engineering, Montana State University, April 2006.