Mechanisms of Biofilm Formation in B. subtilis and P. aeruginosa

Most often studied in their planktonic state, many bacteria also form multicellular communities, referred to as biofilms, through complex communication. These biofilms significantly affect the survivability and specialization... [ view full abstract ]

Most often studied in their planktonic state, many bacteria also form multicellular communities, referred to as biofilms, through complex communication. These biofilms significantly affect the survivability and specialization of their constituents, and are held together by an elaborate matrix of proteins, carbohydrates, and extracellular (e)DNA. Many biofilms enable pathogens to colonize unique host niches, and can evade immune response and antibiotic therapy. Biofilms typically grow on agar-air interfaces, known as colonies, or on liquid-air interfaces, called pellicles. The first goal of my project was to identify conditions that enable a consistent development of phenotype-expressing colonies and pellicles in both gram-positive Bacillus subtilis and gram-negative Pseudomonas aeruginosa. After optimizing growth conditions, we tested the phenotypic response of biofilms to oxygen availability and found that hypoxic conditions are likely to induce a “wrinkled” phenotype in which the surface of the biofilms fold to improve access to oxygen. This phenotype was not observed in bacteria containing redox-sensitive signals (phenazines) that shuttle electrons from oxic to anoxic regions. Lastly, structural microscopic studies revealed localization of living cells to the top and bottom surfaces of colonies, highlighting the importance of oxygen access in biofilm formation.