Much of the work in my lab focuses on the study of surface-attached microbial communities known as biofilms. These surface attached communities can be found in medical, industrial and natural settings. In fact, life in a biofilm probably represents the predominate mode of growth for microbes in most environments. Biofilm microbes are typically surrounded by an extracellular matrix, which provides structure and protection to the community. Biofilm-grown bacteria are notorious for their resistance to a range of antimicrobial agents including clinically relevant antibiotics. Key goals of my lab are to understand how biofilms form on both living (airway cells) and non-living (medical implant) surfaces. We are also interested in the role of biofilms in host-pathogen interactions and resistance to antibiotic therapy.
Research in the O'Toole Lab
A central interest in the lab is the understanding of how bacteria transition from a planktonic (free-swimming) mode of growth to life in a biofilm. Using the model organism Pseudomonas aeruginosa, an opportunistic human pathogen, our studies show that the unusual intracellular signaling molecule cyclic-di-GMP controls early biofilm formation by regulating both surface motility and exopolysaccharide production. More recent work from the group has addressed the question of whether bacteria can sense a surface - we think they can. We are using a combination of genetic and single-cell studies to address this question.
How do other microbes regulate biofilm formation? Like P. aeruginosa, cyclic-di-GMP regulates biofilm formation by the soil organism Pseudomonas fluorescens, but using a very different mechanism. This soil microbe uses cyclic-di-GMP to regulate the localization of a large surface adhesion critical for biofilm formation. Our work has uncovered a novel "inside-out" signal transduction pathway that allows the cell to control localization of this adhesin in response to changing pools of cyclic-di-GMP inside the cell. We recently reported biochemical and structural studies that shows a new mechanism of periplasmic proteolysis controlling biofilm formation by this organism. We have also employed atomic force microscopy to understand how the large adhesin LapA allows this microbe to initiate biofilm formation.
Biofilm formation and disease. P. aeruginosa forms biofilms in the lungs of patients suffering from the disease cystic fibrosis (CF), which is caused by a mutation in the CFTR chloride channel. Together with the Stanton group at Dartmouth, we have developed a new model system for growing biofilms on airway cells derived from CF patients to better understand the role of host interactions with bacterial biofilms. Using this system, we have begun to study the role of polymicrobial communities in these infections. These studies have been guided by our work analyzing the microbiome of the CF airway. For example, we have been exploring the interactions between P. aeruginosa and Streptococci spp. Our findings show that microbes in co-culture often behave very differently than microbes in single culture.
Host-pathogen interactions. As part of an ongoing collaborative study with the Stanton and Madden groups at Dartmouth, we have been studying the Cif toxin of P. aeruginosa. This toxin alters the membrane expression of CFTR, thereby altering function of the host cell. Interestingly, Cif is delivered directly to the host cell via outer membrane-derived vesicle structures. The toxin is an epoxide hydrolase enzyme and we have solved its 3D structure. We are currently trying to understand the mechanism by which Cif alters trafficking of CFTR.
Phage lysogeny and biofilm formation. lnteractions between bacteria and bacteriophages (i.e., viruses) are common in nature. Our lab discovered that infection of P. aeruginosa with the phage DMS3 blocks the ability of this microbe to make a biofilm. The DMS3-mediated loss of biofilms formation also requires an unusual repeat structure on the chromosome of P. aeruginosa, called a CRISPR region. We are trying to learn how the interactions between bacteria and bacteriophage might impact key group behaviors like biofilm formation.
Vector tools. Over the past few years our lab has developed new vectors that take advantage of the power of yeast in vivo recombination. These tools have proven very useful in the lab, and additional information about the vectors can be found at this link.