Bacterial adhesion and metabolic activity: Investigation of the link between the charge-regulated nature of the bacterial cell surface and cellular bioenergetics
The principal objective of this proposal is to investigate the effect of bacterial adhesion to surfaces on metabolic activity, and to develop a predictive model of how the properties of a surface will affect Äp and cellular ATP levels of adhered bacteria. The research hypothesis is that there is a direct link between bacterial adhesion and the proton motive force that forms across the bacterial membrane, with the result being a shift in the pH at the cell surface. The project incorporates both microbial biology techniques and numerical modeling to study the impact of bacterial adhesion, surface properties, and divalent concentration on bacterial cellular energetics.
It is anticipated that this study will show (1) that there is a direct link between bacterial adhesion to a surface and changes to Äp; (2) that these changes to Äp are due to a shift in pH at the cell surface upon adhesion; and (3) that these changes to Äp will be a function of the bacterial and solid surface properties and multivalent cation concentration in the bulk solution, as predicted by the charge regulation effect. If the hypothesis is shown to be true, this will open up a spectrum of new research areas in microbiology and microbial ecology (e.g., understanding how cells make use of this enhanced Äp and ATP, such as altering cellular growth yields or initiating other processes upon adhesion, such as cell signaling and production of extracellular polymers for biofilm formation), and environmental engineering, bioengineering and materials science (e.g., engineered design and application of surfaces to achieve desired enhancements or reductions in metabolic activity, such as with bioreactors, medical devices and implants, and pipelines). A key component of this project is the integration of research with education by involving graduate, undergraduate and high school students.
A key aspect with bacterial surface growth is how the bacteria interact with the surface upon which they have adhered: does the surface stimulate growth and colonization or does it inhibit growth and cause the bacterium to die? This adhesion has implications in a wide array of applications, including attached-growth bioreactors; biodegradation of contaminants in soils; soil nutrient cycling; surface corrosion; bacterial survival in soil and water filtration systems; pathogenic biofilm formation on medical implants and equipment; and biofilm formation in water distribution systems. From an engineering standpoint the "Holy Grail" is to a priori select and design passive surface materials that enhance or inhibit the growth of attached bacteria. Studies have shown that bacterial metabolic activity can be altered upon adhesion to a solid surface, and while these studies indicate that bacterial attachment to surfaces can directly affect metabolic activity, the mechanisms for this altered activity are unclear. To address this knowledge gap, this study examined a hypothesis developed by the Principal Investigator that considers specific physiochemical interactions between the surface and the bacterial cell wall and the impacts of these interactions on cellular bioenergetics. This hypothesis is outlined in Figure 1. The approach to investigate the hypothesis used a combination of experimental and numerical investigations to systematically examine how the ATP concentration of attached bacteria is affected by the properties of the surface to which the cells are adhering. Through these investigations we verified that the ATP concentration of bacteria is affected by adhesion as predicted by the working hypothesis. This was demonstrated both for surfaces resulting in enhanced ATP concentrations and for those resulting in reduced ATP concentrations and thus exhibit antimicrobial properties. Additionally, the direct link between changes in external pH at the cell surface and changes in ATP concentration was experimentally verified. This study demonstrated that the working hypothesis describes an important relationship between surface properties and the metabolic activity of attached bacteria. Example applications of these results include antimicrobial activated carbon for use in water treatment systems; surface coatings in water pipelines that inhibit microbial colonization without leaching harmful chemicals into the water; and surface coatings and materials selection to reduce infections on medical implants such as catheters. Overall, these results provide a framework for the informed selection and design of surfaces and surface coatings to enhance or inhibit bacterial colonization.
