Date of Award

Summer 8-15-2023

Document Type

Thesis (Master's)

Department or Program

Master of Arts in Liberal Studies

Abstract

Bacterial biofilms are held together by various, often species specific, secreted proteins, polysaccharides, and DNA – collectively termed the biofilm matrix. Although biofilms have many fitness advantages conferred to them, matrix mutants are abundant within natural isolates, implying context-dependent disadvantages inherent to the production of some matrix components. Here we explore how biofilm architecture controls a tradeoff in the context of different predation pressures. The model organism Escherichia coli is used as a prey species, due to its highly characterized protection against bacteriophages, and the motile bacterial predator Bdellovibrio bacteriovorus as the predatory exposure. We use microfluidics paired with confocal microscopy to answer questions relating to the spatial ecology of biofilm communities. Using a Matlab software called Biofilm Q, these spatial dynamics can be precisely quantified and graphed. We show that stable biofilm architecture can decrease the fitness of E. coli when exposed to the bacterial predator B. bacteriovorus. In E. coli, mature biofilm structural rigidity is largely controlled by curli fimbria matrix protein. While the curli fiber mesh can protect E. coli from bacteriophage exposure within biofilms, B. bacteriovorus is retained by the rigid biofilm structure that curli promotes. Further, this predator is capable of maneuvering through the matrix to access its prey. E. coli survival is only observed when there are mass dispersal events (sloughing) that clear the curli protein mesh and the majority of invading predators encompassed within it. In matrix mutants lacking curli, E. coli biofilms exhibit higher survival rates, as B. bacteriovorus has less stable biomass to reside in to find new prey. These matrix mutants detach readily when disrupted by a predator, and thus clear the infection immediately. Our results illustrate that the same E. coli extracellular matrix component that is necessary for protection from bacteriophages also causes susceptibility to predation by B. bacteriovorus. Protection against different sources of predation pressure can thus trade off against each other within biofilms, which may help to explain natural variation in the propensity to produce highly matrix-stabilized versus easily dispersing biofilms in the wild.

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