Interspecies bacterial communication

Decades of microbiology research have focused on studying bacterial species in isolation, yet this is rarely how microbes live in nature. Instead, they exist in complex polymicrobial communities, where species may interact peacefully or aggressively towards other members of the community. We are interested in understanding the microbial signals community members use to communicate between species which drive these interactions.

The image to the left shows Pseudomonas aeruginosa swarming towards Staphylococcus aureus when inoculated on an agar surface. Notice the thickened swarm front proximal to the yellow S. aureus colony. 

Interspecies behaviors during infection

Accumulating evidence suggests that polymicrobial interactions influence microbial survival and behavior during chronic infection, such as those in the airways of cystic fibrosis (CF) patients. Our studies in CF patients reveal an association with coinfection with the bacteria Pseudomonas aeruginosa and Staphylococcus aureus and a decline in lung function. We seek to understand why coinfected patients have poor outcomes and particularly how interspecies interactions influence the course of the disease.

The image to the right shows mixed aggregates of Pseudomonas and Staphylococcus identified in the sputum of a cystic fibrosis patient by utilizing fluorescence in situ hybridization combined with a modified passive clearing methodology designed to retain the spatial organization of microbial communities in sputum for in situ identification of microorganisms. Pseudomonas is indicated in green, Staphylococcus in magenta, and regions of colocalization appear white (white arrows).

Tracking polymicrobial dynamics


To study how microbial species interact, we have developed a range of tools to monitor polymicrobial behaviors in real-time. We can now observe interspecies behavior from their initial encounters through development of mixed microbial communities. We use widefield, epifluorescence, and confocal imaging modalities to monitor bacterial motility, biofilm formation, and gene expression in response to other microbial species.

In the movie on the left, P. aeruginosa responds to secreted products made by S. aureus from a distance. Single P. aeruginosa cells increase motility, break off from a growing colony, and move towards S. aureus (movie, left).  Below, a particle-tracking algorithm identifies and tracks single bacterial cells. Each color represents the track of a different P. aeruginosa cell. Introducing a Cys residue in FliC allows flagllum visualization with Alexa Fluor488 C5 Maleimide. Flagella can be tracked over time by serial staining.