Influence of the hydrodynamic environment on quorum sensing in Pseudomonas aeruginosa biofilms

Abstract

We provide experimental and modeling evidence that the hydrodynamic environment can impact quorum sensing (QS) in a Pseudomonas aeruginosa biofilm. The amount of biofilm biomass required for full QS induction of the population increased as the flow rate increased.

FIG. 1.

Comparison of the amounts of biofilm biomass required for full QS induction of the population from model simulations (▪) and from tube biofilm reactor experiments (□). The three modeled data points that were tested experimentally are circled.

FIG. 2.

Schematics depicting tube biofilm reactors. (A) Once-through reactor for flow in the laminar regime. (B) Recycle reactor for flow in the transitional regime between laminar and turbulent.

FIG. 3.

Accumulation of biofilm biomass in the tube biofilm reactor. Flow in the laminar regime, 0.04 ml/min (□) and 4.0 ml/min (▪); flow in the transitional regime between laminar and turbulent, 380 ml/min (×). Lines on the plot show the trend of the data. For simplicity, error bars representing the standard deviations are shown only for the data points that are based on the averages of at least two separate harvested biofilms. The data points without error bars are based on results from a single harvested biofilm. The biofilm biomass for each harvested biofilm was measured by triplicate plate counts.

FIG. 4.

QS induction in the tube biofilm reactor. Flow rates were (A) 0.04 ml/min, (B) 4.0 ml/min, and (C) 380 ml/min (with and without stagnation). The vertical dashed line indicates the biofilm biomass at which QS was fully induced (i.e., lasB expression at 100% of planktonic maximum).

FIG. 5.

QS induction in the flow cell biofilm reactor. Transmitted light and epifluorescent maximum projections of the confocal scanning laser microscopy stacks are shown for a biofilm grown in the flow cell at 1 ml/min. (A) Transmitted light image and (B) corresponding epifluorescent image showing low lasB expression in the biofilm under flowing conditions. (C) Transmitted light image and (D) corresponding epifluorescent image showing full lasB expression after a 6-h stagnation period.