Biofilms are populations of microbes that adhere to surfaces by means of a self-synthesized extracellular matrix. In the Darby laboratory, we investigate biofilms that pathogenic bacteria make to persistently colonize their hosts and vectors.

Yersinia pestis, the causative agent of bubonic plague, produces a biofilm to colonize its vector, the flea. The biofilm blocks the flea’s digestive tract and starves the insect, stimulating it to bite in attempts to feed and thus spread the bacteria to new hosts. We use the nematode worm Caenorhabditis elegans as a surrogate for fleas, allowing robust genetic analysis of the host as well as the pathogen. Y. pestis makes a biofilm that covers the mouth of C. elegans and prevents the worm from feeding, and this overlaps with flea blockage physically, functionally and genetically. We are determining the genetic pathways of Y. pestis biofilm synthesis, and in complementary work are analyzing the polysaccharide-rich biofilm chemically. In addition, we have obtained numerous C. elegans mutants to which the biofilm cannot bind. Analysis of these mutants will provide information on the surface composition and organization of the nematode, about which little is known. by combining data from the bacterial and nematode sides of the interaction, we plan to develop a complete molecular description of the biofilm matrix adhesion to the nematode.

Several additional projects addressing bacterial biofilms are in progress or planned.