AbstractsBiology & Animal Science

In this dissertation, we find that Staphylococcal biofilm microstructure is highly dependent on growth environment. Biofilms consist of structured communities of cells encapsulated in matrix materials, and are frequently responsible for clinical infections. We found that Staphylococcus epidermidis biofilm microstructure is heterogeneous in both unstressed and stressed (NaCl and sub-lethal vancomycin) conditions. Unstressed biofilms contained high-, medium-, and low-density phenotypes, and stressed biofilms had medium- and low-density phenotypes. High-density biofilms contained densely packed, disordered structures, while low-density biofilms contained open, porous structures. We used our understanding of microstructure to create bacterial-chitosan constructs with high- and low-density phenotypes and creep compliances matching natural biofilms through self-assembly of cells and chitosan at pH > 7. The phase instability of chitosan controlled the mechanical behavior of these constructs. We compared the phase instability of chitosan to that of S. epidermidis biofilm matrix materials. Chitosan was unstable at pH > 7, while matrix materials were unstable at pH < 7. We increased the pH of a S. epidermidis biofilm and found that the biofilm softened at pH > 7. S. aureus biofilms also softened at pH > 7. We extended our work on biofilm structure by investigating structure of multispecies biofilms of S. aureus and S. epidermidis. In multispecies biofilms, S. aureus is the dominant species in unstressed conditions (pH 7, 37??C), at high pH (8, 9) and at high temperature (45??C). S. epidermidis is the dominant species when multispecies biofilms are grown at low pH (5) and in 1.0 ??g/mL vancomycin. We also investigated a label-free method for imaging S. epidermidis biofilm microstructure. We found that cellular microstructure was revealed using confocal Raman microscopy when samples were thin. Overall, our understanding of biofilm microstructure aids in understanding their mechanical properties and provides ground for development of biofilm control strategies or theoretical models of biofilms. In addition to this fundamental understanding of biofilm microstructure, we investigated interdisciplinary learning in a graduate elective course on biofilms. We found that student self-perception of interdisciplinary learning outcomes related to recognizing disciplinary perspectives and teamwork skills, and interdisciplinary fluency increased over the course of the semester.