THE EFFECT OF BIOPOLYMER PROPERTIES ON BACTERIAL ADHESION: AN

338 Pages·2003·3.57 MB·English

Worcester Polytechnic Institute
Department of Chemical Engineering

THE EFFECT OF BIOPOLYMER PROPERTIES ON BACTERIAL ADHESION:
AN ATOMIC FORCE MICROSCOPY (AFM) STUDY

A Thesis in
Chemical Engineering

By
Nehal Ibrahim Abu-Lail

Copyright 2003 Nehal Ibrahim Abu-Lail

Submitted in Partial Fulfillment
Of the Requirements
for the Degree of

Doctor of Philosophy

September 12, 2003

Approved: Approved:

------------------------------------------------- --------------------------------------
Terri A. Camesano, Ph.D. Advisor Robert Thompson, Ph.D. Committee
Assistant Professor of Chemical Engineering Professor of Chemical Engineering
Worcester Polytechnic Institute Worcester Polytechnic Institute

Approved: Approved:

------------------------------------------------- --------------------------------------
William Clark, Ph.D. Committee John Bergendahl, Ph.D. Committee
Associate Professor of Chemical Engineering Assistant Professor of Civil and
Worcester Polytechnic Institute Environmental Engineering
Worcester Polytechnic Institute
Abstract
The effect of bacterial surface biopolymers on bacterial adhesion to surfaces was studied
through experiments and modeling. Atomic Force Microscopy (AFM) provided the tool
to measure the interaction forces between different bacterial cells and silicon nitride tips
under different chemical conditions at a nanoscopic level. Two bacterial strains were
considered: Pseudomonas putida KT2442 and Escherichia coli K-12 JM109. This study
addressed the following issues: 1) the effect of solution ionic strength and solvent
polarity on adhesion between Pseudomonas putida KT2442 and the silicon nitride AFM
tip, 2) role of heterogeneity of bacterial surface biopolymers on bacterial adhesion, 3)
role of lipopolysaccharides (LPS) on adhesion at three different scales: continuous, batch,
and nanoscale, and 4) nature of interactions between E. coli JM109 and a model surface
(silicon nitride tip).
To address the first issue, formamide, water, and methanol were used to
investigate the effect of polarity on surface characteristics of biopolymers on the bacterial
surface while a range of salt concentrations between that of water to 1 M KCl were used
to study the effect of ionic strength. The adhesion increased with decreasing polarity of
the solvent, indicating that the polymers on the bacterial surface are hydrophilic in nature.
The adhesion was slightly affected by ionic strength variations up to a concentration of
0.1 M KCl; this may have been due to the fact that the ionic concentration in the solution
did not counterbalance the ionic concentration in the biopolymer brush on the bacterial
surface. However, a dramatic increase in the adhesion magnitude was observed when the
salt concentration increased above 0.1 M KCl. This transition in adhesion with ionic
strength from a low to high value induced a transition in the elasticity of the bacterial
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surface biopolymers. The biopolymer brush layer did change from rigid to soft with
increasing the ionic strength. The elasticity was quantified mainly by the use of the freely
jointed chain (FJC) model.
Our interest in investigating the role of heterogeneity on adhesion developed
from the results of the first study. The bacterial surface polymers were thought to be
different in their chemical and physical nature since they were found to span a range of
segment lengths. Analyzing the adhesion forces for P. putida KT2442 showed that the
bacterial surface is heterogeneous. The heterogeneity was evident on the same cell
surface and between different cells from the same population.
To resolve the third issue, approximately, 80% of the surface LPS of E. coli K-
12 JM109 were removed by treating the cells with 100 mM ethylenediaminetetraacetic
acid (EDTA). The effect of LPS removal on the adhesion of the cells to the silicon nitride
tip was studied in water and phosphate buffered silane (PBS). The adhesion results from
the AFM experiments were compared to batch retention experiments with glass as the
substratum and column attachment experiments with columns packed with quartz sand.
LPS controlled bacterial adhesion to the different surfaces in the study at three scales:
batch, continuous, and nano-scale.
Finally, the nature of interactions between E. coli JM109 and a model surface
(silicon nitride tip) were investigated in solvents of varying polarity (formamide, water,
and methanol). The Young’s modulus of elasticity for the bacterial surface was estimated
by fitting of the Hertzian model to the force-indentation curves. Young’s modulus values
increased as the solvent polarity decreased, indicating a stiffer bacterial surface in lower
polarity solvents. The average adhesion force in each solvent was negatively correlated
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with the dielectric constant of the solvent, suggesting hydrophilic biopolymers. Specific
and non-specific interaction forces between the AFM tip and the biopolymers were
further characterized by applying a Poisson statistical analysis to the discrete adhesion
data. The specific and non-specific interaction forces were the highest in methanol (-4
and -1.48 nN respectively). These values are in accordance with the high adhesion
magnitude values measured with AFM in methanol. The results of my different studies
emphasized the important role of AFM in studying biological interactions to different
surfaces and in characterizing bacterial surface biopolymers.
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Table of contents
Page
List of Tables……………………………………………………………………….. …x
List of Figures………………………………………………………………………. ...xi
Acknowledgments…………………………………………………………………... ..xvii

Chapter 1: Introduction……………………………………………………………... ….1
1.1 Problem Statement and Research Objectives……………………….. ….1
1.2 Literature Review…………………………………………………… ….5
1.2.1 Elasticity of Biopolymers……………………………………… ….6
1.2.2 Steric Interactions between the Biopolymers and the AFM Tip. ….7
1.2.3 Effect of Bacterial Biopolymers on Adhesion…………………. ….9
1.2.4 Elasticity of the Cell…………………………………………… …10
1.2.5 Bacterial Adhesion……………………………………………... …11
1.2.5.1 AFM Studies……………………………………………. …11
1.2.5.2 Attachment during Flow……………………………… …12
1.2.6 Statistical Analysis of AFM data……………………………… …12
1.2.7 Force Balances and Interaction Energy………………………... …13
1.3 Organization of Dissertation………………………………………… …15
1.4 References…………………………………………………………… …20

Chapter 2: Elasticity of Pseudomonas putida KT2442 Surface
Polymers Probed with Single-Molecule Force Microscopy …………… …33
Abstract………………………………………………………………….. …33
2.1 Introduction………………………………………………………….. …35
2.2 Materials and Methods………………………………………………. …38
2.2.1 Cultures………………………………………………………... …38
2.2.2 Sample Preparation……………………………………………. …39
2.2.3 Polymer Characterization……………………………………… ...39
2.2.4 Zeta Potential………………………………………………….. …39
2.2.5 Polarimetry……………………………………………………. …39
2.2.6 Force Analysis Using AFM…………………………………… …40
2.2.7 Retraction Curves……………………………………………… …40
2.2.8 Modeling………………………………………………………. …41
2 .3 Results………………………………………………………………. …42
2.3.1 Effect of Salt Concentration on Biopolymer
Conformation and Adhesive Forces…………………………... …42
2.3.2 Effect of Solvent Polarity on Biopolymer
Conformation and Adhesive Forces…………………………... …43
2.3.3 Comparison with Polymer Elasticity Models………………… …44
2.3.3.1 The Effect of Solution Ionic Strength………………… …44
2.3.3.2 Effect of Solvent Polarity…………………………….. …44
2.3.3.3 Comparison of WLC and FJC Models……………….. …45
2.3.3.4 Extensible Freely Jointed Chain Model………………. …46
2.4 Discussion…………………………………………………………... …46
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2.4.1 Effect of Polarity and Ionic Strength on
Biopolymer Conformation …………………………………… …46
2.4.2 Biopolymer Elastic Properties………………………………... …48
2.4.3 Comparison Between Different Models……………………… …48
2.4.4 Biopolymer Adhesion………………………………………… …49
2.4.5 Heterogeneity of Biopolymers………………………………... …51
2.4.6 Chemical Nature of the Biopolymer………………………….. …52
2.5 Summary……………………………………………………………. …53
2.6 Acknowledgments…………………………………………………... …54
2.7 References…………………………………………………………... …55
2.8 Figure Captions……………………………………………………... …67

Chapter 3: Heterogeneity in Bacterial Surface Polysaccharides, Probed
On Single-Molecule Basis ……………………………………………... …81
Abstract…………………………………………………………………. …81
3.1 Introduction…………………………………………………………. …83
3.2 Materials and Methods……………………………………………… …85
3.2.1 Cultures……………………………………………………….. …85
3.2.2 Bacterial Cell Preparation for AFM Measurements………….. …85
3.2.3 Single-Molecule Force Spectroscopy ………………………... …85
3.2.4 Modeling Biopolymer Elastic Properties……………………... …86
3.2.5 Polymer Characterization……………………………………... …87
3.2.6 Size-Exclusion Chromatography……………………………... …87
3.2.7 Polarimetry……………………………………………………. …87
3.3 Results………………………………………………………………. …88
3.3.1 Single-Molecule Force Spectroscopy………………………… …88
3.4 Discussion…………………………………………………………... …90
3.4.1 Physical Heterogeneity……………………………………….. …90
3.4.2 Chemical Heterogeneity………………………………………. …90
3.4.3 Effect of Solution Ionic Strength……………………………... …92
3.4.4 Adhesion Affinities…………………………………………… …93
3.5 Acknowledgments…………………………………………………... …94
3.6 References…………………………………………………………... …95
3.7 Figure Captions……………………………………………………... ..103

Chapter 4: Role of Ionic Strength on the Relationship of Biopolymer
Conformation, DLVO Contributions, and Steric Interactions to
Bioadhesion of Pseudomonas putida kT2442 ………………………….. ..112
Abstract…………………………………………………………………. ..112
4.1 Introduction…………………………………………………………. ..114
4.2 Materials and Methods……………………………………………… ..117
4.2.1 Bacterial Culture Preparation…………………………………. ..117
4.2.2 Electrophoretic Mobility……………………………………… ..117
4.2.3 Preparing Bacterial Samples for AFM Work…………………. ..117
4.2.4 Force Analysis Using AFM…………………………………... ..118
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4.2.5 Determination of Polymer Brush Layer Thickness…………… ..119
4.2.6 Calculation of Surface Potential for Soft Particles…………… ..120
4.2.7 Calculation of Interaction Energies…………………………… ..121
4.2.8 Polymer Elastic Properties……………………………………. ..122
4.2.9 Scaling Relationships for Polyelectrolyte Brushes…………… ..122
4.3 Results………………………………………………………………. ..125
4.3.1 Biopolymer Electrostatic Properties and Predicted Energy
Barriers to Attachment Based on Soft-Particle DLVO Theory ..125
4.3.2 Biopolymer Conformation……………………………………. ..125
4.3.2.1 Thickness of the Polymer Brush Layer……………….. ..125
4.3.3 Elastic Properties of the Biopolymers………………………… ..126
4.3.4 Scaling Relations………………………………………………….. ..127
4.3.5 Effect of Ionic Strength on Biopolymer Adhesion……………….. ..128
4.4 Discussion……………………………………………………………… ..128
4.4.1 Effect of Ionic Strength on Biopolymer Conformation………….. ..128
4.4.2 Polyelectrolyte Theories…………………………………………. ..129
4.4.3 Balance of Attractive and Repulsive Forces…………………….. ..131
4.4.4 Critical Salt Concentrations Influencing Biopolymer
Conformation and Adhesion……………………………………... ..133
4.5 Summary………………………………………………………………. ..135
4.6 Acknowledgments……………………………………………………... ..135
4.7 Glossary……………………………………………………………….. ..136
4.8 Figure Captions………………………………………………………... ..142
4.9 Appendix………………………………………………………………. ..145
4.9.1 Soft-Particle DLVO Theory……………………………………... ..145
4.9.2 Born Repulsive Interactions……………………………………... ..145
4.10 References……………………………………………………………. ..148

Chapter 5: The Role of Lipopolysaccharides in Adhesion, Retention,
And Transport of Escherichia coli JM109……………………………… ..168
Abstract…………………………………………………………………. ..168
5.1 Introduction…………………………………………………………. ..170
5.2 Materials and Methods……………………………………………… ..173
5.2.1 Cultures……………………………………………………….. ..173
5.2.2 Removal of Lipopolysaccharides via EDTA Treatment……… ..173
5.2.3 Protein Assay…………………………………………………. ..174
5.2.4 Electrophoretic Mobility Measurements……………………… ..174
5.2.5 Atomic Force Microscopy Experiments……………………… ..175
5.2.6 Modeling of Approach Curves with a Steric Model:
Determination of Polymer Brush Thickness………………….. ..176
5.2.7 Classical DLVO Theory Calculations of Interaction Energies.. ..177
5.2.8 Soft Particle DLVO Theory…………………………………... ..178
5.2.9 Modeling of Retraction Curves: Statistical Distributions of
Adhesion Affinities…………………………………………… ..180
5.2.10 Batch Retention Assays……………………………………... ..180
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5.2.11 Bacterial Transport in Porous Media………………………... ..181
5.3 Results………………………………………………………………. ..183
5.3.1 AFM Adhesion Measurements-Effect of LPS on Adhesion …. ..183
5.3.2 Distribution of Adhesion Affinities…………………………... ..184
5.3.3 Steric Interactions…………………………………………….. ..185
5.3.4 Energy Calculations using DLVO Theory…………………… ..185
5.3.4.1 Zeta Potential and Soft-particle Potential of E. coli
JM109………………………………………………… ..185
5.3.4.2 Interaction Energies between E. coli JM109 and Sand. ..186
5.3.4.3 Interaction Energies between E. coli JM109 and
Silicon Nitride………………………………………… ..186
5.3.5 Batch Retention Experiments………………………………… ..187
5.3.6 Column Transport Experiments………………………………. ..187
5.4 Discussion…………………………………………………………... ..188
5.4.1 Effect of EDTA Treatment on Cell Surface Macromolecules... ..188
5.4.2 Role of Electrostatic Interactions Controlling the Attachment
of E. coli to Silicon Nitride, Glass, and Quartz Sand………… ..189
5.4.3 Role of Steric Interactions Produced by Lipopolysaccharides
in Bacterial Adhesion………………………………………… ..190
5.4.4 Interpreting Bacterial Heterogeneity in Adhesion Force…….. ..191
5.4.5 Relating Biopolymer Properties to Bacterial Transport …….. ..192
5.5 Acknowledgments…………………………………………………... ..194
5.6 References…………………………………………………………... ..195
5.7 Figure Captions……………………………………………………... ..207

Chapter 6 : Nature of the Interaction Forces between Escherichia coli JM109 and
A Model Surface……………………………………………………… ..221
Abstract……………………………………………………………….. ..221
6.1 Introduction……………………………………………………….. ..223
6.2 Materials and Methods……………………………………………. ..226
6.2.1 Experimental Procedures……………………………………. ..226
6.2.1.1 Cultures……………………………………………… ..226
6.2.1.2 Atomic Force Microscopy Experiments…………….. ..227
6.2.1.3 Contact Angle Measurements……………………….. ..228
6.2.2 Modeling…………………………………………………….. ..228
6.2.2.1 Statistical Description of AFM Data………………… ..228
6.2.2.2 Analysis of the Adhesion Force Data from AFM
Retraction Curves……………………………………. ..229
6.2.2.3 Application of Poisson Distribution Function to AFM
Pull-off Force Data to Characterize Bonds Formed…. ..229
6.2.2.4 Poisson Statistical Analysis………………………….. ..230
6.2.2.5 Elasticity of Microbial Cells…………………………. ..232
6.2.2.6 Bacterial Cell Elasticity is Characterized by the
Young’s Modulus…………………………………….. ..233
6.2.2.7 Modeling Adhesion Forces between Elastic Surfaces.. ..233
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6.2.2.8 Surface Energy Calculations…………………………. ..238
6.2.2.9 van der Waals Force and Energy Interactions………. ..239
6.2.2.10 Modeling of Approach Curves with a Steric Model:
Determination of Polymer Brush Thickness……….. ..240
6.3 Results……………………………………………………………… ..240
6.3.1 Elasticity and Adhesion Models……………………………… ..240
6.3.1.1 Elasticity of Bacterium……………………………….. ..240
6.3.1.2 Adhesion Models……………………………………... ..241
6.3.2 Relationships Between Solvent Polarity and Adhesion Other
Properties…………………………………………………….. ..242
6.3.3 Specific and Non-specific Forces…………………………..... ..244
6.4 Discussion………………………………………………………….. ..246
6.4.1 Effect of Polarity on Biopolymer Conformation and Bacterial
Adhesion………………………………………………………. ..246
6.4.2 The Role of Interaction Forces in Controlling the Adhesion of
E. coli JM109 to Silicon Nitride…………………………....... ..249
6.4.3 Elasticity of the Cell…………………………………………. ..254
6.4.4 Adhesion Models…………………………………………… ..255
6.5 Glossary…………………………………………………………….. ..260
6.6 Figure Captions…………………………………………………….. ..262
6.7 References………………………………………………………….. ..264

Chapter 7: Conclusions and Recommendations……………………………………. ..292
7.1 Conclusions…………………………………………………………. ..292
7.2 Recommendations for Further Study ………………………………. ..296
7.2.1 Accurate Estimation of the Tip Radius……………………….. ..296
7.2.2 Estimation of Cantilever Spring Constant……………………. ..297
7.2.3 Finding the Zero Separation Distance between the AFM
Tip and the Substrate…………………………………………. ..298
7.2.4 Bacterial and Adhesion Models………………………………. ..299
7.2.5 Chemical Force Microscopy to Probe Bacterial-Natural
Organic Matter Interactions………………………………….. ..300
7.2.6 The Use of Peptides as Biosensors…………………………… ..301
7.3 References………………………………………………………….. ..303
7.4 Figure Captions ……………………………………………………. ..307

Appendix……………………………………………………………………………. ..316
A.1 Energy Calculations using DLVO Theories………………………… ..316
A.2 Reproducibility in Force Measurements……………………………. ..316
A.3 Figure Captions……………………………………………………… ..320

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List of Tables

Table Page

Table 2.1 Effect of Solvent on Average Properties of Adhesion Peaks……….. …65
Table 2.2 Summary of Model Parameters for Surface Biopolymers of
Pseudomonas putida KT2442………………………………………. …66
Table 3.1 Summary of the Parameters Used to Fit the Solid Lines in
Figure 3.4. The average segment length was 0.21 ± 0.08 nm, average
contour length was 273 ± 250 nm, and the average R2 was 0.95 ±
0.07. Values are shown in order of increasing contour
length………………………………………………………………... ..101
Table 3.2 Summary of the mean and standard deviation of pull-off distances
and pull-off forces for the data shown in Figure 3.6………………... ..102
Table 4.1 Summary of Parameters for DLVO Interaction Energy Calculations. ..138
Table 4.2 Physical Properties of Brush Layer as a Function of Salt
Concentration……………………………………………………….. ..139
Table 4.3 Comparison of Measured Adhesion Forces with DLVO Predictions
as a Function of Added Salt Concentration…………………………. ..140
Table 4.4 Summary of Physical Property Transitions as a Function of Added
Salt Concentration ………………………………………………….. ..141
Table 5.1 Application of Steric Model to AFM Approach Curves for E. coli
JM109……………………………………………………………….. ..209
Table 5.2 Evaluation of Surface Potentials of E. coli JM109 Using both
Conventional Smoluchowski Thepry (Zeta Potential) and Soft-
Particle Theory………………………………………………………. ..210
Table 5.3 Summary of E Values for Calculations of Interaction Energy
max
between E. coli and Different Substrates……………………………. ..211
Table 5.4 Bacterial Transport Experiments in Quartz Sand Packed Columns.... ..212
Table 6.1 Contact Angle Measurements on E. coli JM109……………………. ..275
Table 6.2 Young’s moduli for E. coli JM109………………………………….. ..276
Table 6.3 Correlation of Bacterial Surface Properties Obtained from
Interaction Force Measurements with Solvent Properties…………… ..277
Table 6.4 Summary of Adhesion Forces Measured by AFM…………………... ..278
Table 6.5 Summary of Calculated Parameters Based on Fitting Poisson
Distribution to Adhesion Force Data………………………………... ..279
Table 6.6 Summary of Forces and Energies in Different Solvents…………….. ..280
Table 6.7 Summary of the Adhesion Map Parameters Constructed by Johnson
et al. [53]…………………………………………………………….. ..281

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