1. COLLEGE OF ENGINEERING Chemical, Biological & Environmental Engineering
RHEOLOGY OF PSEUDOMONAS
AERUGINOSA BIOFILM Uranbileg Daalkhaijav and Travis Walker
Results and Discussions
OBJECTIVE
Understand the rheological properties of P.
aeruginosa biofilm and determine the impact of
salt concentration and glycerol concentration on
these rheological properties.
MATERIALS AND METHODS
Culture and medium
• Pseudomonas aeruginosa wild type (PAO1)
• Lysogeny broth (LB)
• Salt concentration: 1 – 6.5% w/w NaCl
• Glycerol concentration: 0 – 12.5% w/w
Rheological testing
• 40 mm SS flat plate geometry
• Amplitude sweep: frequency 0.5 rad/s
• Frequency sweep: torque 0.01 mN.m
VISCOELASTICITY
Applied torque 0.1 mN.m for 5 minutes and
allowed to recover for 10 minutes à creep
recovery test.
A: elastic response to applied stress
B: viscous response to applied stress
C: elastic recovery from stress
D: viscous recovery from stress
Introduction Research
ABSTRACT
Pseudomonas aeruginosa is an
environmental bacteria that is known for its
ability to produce alginate incased biofilm.
It can cause major problems in the medical
field as an opportunistic pathogen.
Rheology is the study of material behavior
in response to applied stress. From
preliminary studies, P. aeruginosa biofilm is
viscoelastic and shows predominantly
elastic property. The elastic modulus
describes the resistance to deformation or
the solid-like behavior of a material, so this
property is likely responsible for P.
aeruginosa biofilm robustness in the face of
outside stresses.
FUTURE WORK
Salt concentrations from 1% - 20%
Glycerol concentration from 1% - 20%
Different types of salts for its impact on
biofilm rheology
Different types of sugars for its impact on
biofilm rheology
ACKNOWLEDGEMENTS
Skip Rochefort, Martin Schuster, and
Dipankar Koley.
• G’: elastic modulus
• G”: viscous modulus
• P. aeruginosa biofilm has a linear
viscoelastic region (LVR)
between 0.05 – 5.0% strain.
• Yield point was at 5.0% strain
where biofilm starts deforming.
• Biofilm is elastically dominated
over 0.05 – 2 rad/s frequencies.
• Glycerol addition increased the
strength of the biofilm gel.
• Salt addition reduced the
elasticity of the biofilm.
0.01
0.1
1
0.01 0.1 1 10
Modulus(Pa)
Frequency (rad/s)
0.01
0.1
1
0.01 0.1 1 10
Modulus(Pa)
Frequency (rad/s)
0.01
0.1
1
0.01 0.1 1 10
Modulus(Pa)
Frequency (rad/s)
-3
-2
-1
0
1
2
3
4
5
6
7
0 200 400 600 800 1000
Strain(%)
Time (s)
A
C
B
D
Color code green red cyan blue orange
Medium LB LB LB LB LB
NaCl (wt. %) 1 2 6.5 1 1
Glycerol (wt. %) 0 0 0 10 12.5
SALT CONCENTRATION
• LVR for low salt concentration
biofilm was between 0.05% -
5.0% while high salt
concentration was 0.05% - 3.0%
strain
• Increased salt concentration
caused a drop in viscoelasticity
of biofilm and lowered its yield
strain.
GLYCEROL CONCENTRATION
• Glycerol added biofilm yielded at
the same strain as the biofilm
grown in LB.
• Increasing glycerol concentration
from 10% to 12.5% had no effect
on the viscoelasticity of the
biofilm.
• At glycerol concentrations higher
than 12.5%, there is no biofilm
growth.
,