(136j) Self-Similar Dynamics of Extracellular Matrix Production during Bacterial Biofilm Colony Expansion

Introduction: Bacterial biofilms are multicellular microbial communities encased in a self-produced extracellular matrix. Understanding the growth and adhesion of biofilms and their interaction with surfaces is critically important in diverse industrial and medical scenarios, such as in preventing fouling of marine vehicles and halting bacterial growth in implants and medical devices. In this work, we use Bacillus Subtilis biofilms as a model organism to investigate the spatiotemporal dynamics of cell heterogeneity that gives rise to the collective growth and colonization on solid/air interfaces.

Materials and Methods: A triple transcriptional reporter (NCIB 3610 sacA::Phag-mkate2 amyE::PtapA-cfp ywrK::PsspB-citrus) was constructed to simultaneously visualize motility, matrix production and sporulation cell states in the developing biofilm. This strain was grown on a 1.5 wt% MSgg/Agar solid interface at 30 C. Simultaneous time-lapse brightfield and epifluorescence microscopy for each channel was performed every 10 minutes, for a duration of 72 hrs. The resulting movies were analyzed to determine the azimuthally averaged height profiles and transcriptional reporter activity levels for each of the cell types.

Results and Discussion:  Two clear regimes were observed in biofilm growth. At the early stage (t<15 hrs), the exopolysachharide (EPS) matrix is globally produced. The radius of the biofilm exponentially increases with time. At t ~ 24 hrs, there is a transition to a second regime where the size of the colony scales as R~t^0.5. This regime is characterized by a well-defined propagating front where the active growth and production of extracellular matrix (EPS) in the biofilm is localized. The EPS production in the interior of the biofilm is down regulated, along with a simultaneous increase in sporulation activity that is indicative of nutrient starvation. The spatial profile of EPS reporter activity measured from the intensity profiles at the propagating front is self-similar and reaches a final characteristic asymptotic shape during late stage biofilm expansion. The width of this propagating front of the biofilm at the front can be increased by the introduction of fresh glutamate.

Conclusions: We have investigated the collective behavior and dynamics of B. Subtilis biofilms during colony expansion over a solid interfaces. Our results demonstrate the active growth in bacterial biofilms is confined to a locally propagating front. Manipulating the nutrient and environmental conditions at this local front can lead to potential techniques to control biofilm growth.