DYNAMICS SLOWDOWN DURING EARLY STAGES OF BACTERIAL COLONISATION

Groupe Physique des Energies

Laboratoire APC

Université Paris DiderotThomas Vourc’h, Julien Léopoldès, Hassan Peerhossaini

MICRO-ORGANISMS SURFACE INTERACTIONS

o Biofouling

o Infections

o Food-processing industry

o Biofuel production

2

Introduction

T. Bjarnsholt, 2013

yachting-pages.com

famille-schlegel.com

CYANOBACTERIA: PRIMITIVE ORGANISMS

3

Introduction

Evolution of the oxygene rate in atmosphere plotted against time

o Primitive organisms, whichenabled the transition to more evolved forms of life.

Govindjee et Dimitriy Shevala,

2011

CYANOBACTERIA’S POTENTIAL

4

Ducat et al., 2011

Different products from cyanobacteria

Introduction

Photosynthetic efficiency :

o Cyanobacteria : 3 – 9 %

o Average terrestrial

organisms: 0.25 – 3%

M. Brenner, 2006

G. Dismukes et al., 2008

20minutes.fr

BIOFILM FORMATION

5Different stages of biofilm formation

Introduction

C. Cassier-Chauvat

& F. Chauvat, 2015

Mantle of Exopolysaccharides

(EPS)

Typical SEM (scanning electron microscopy) images of

cyanobacterium Synechocystis sp. PCC6803

DIFFERENT KIND OF MOTILITY

6M. Mazza, Journal of Physics D: Applied Physics, 2016

Swimming motility

Swarming motility

Twitching motility

Gliding motilityD. Bhaya et al., Molecular Biology, 2000

Type IV Pili

Introduction

STUDYING DIFFUSION

7

Definition of the Mean Squared Displacement (MSD):

In the case of a 2-D Fickian behaviour:

Introduction

DMSD 4)(

20)()( XXMSD

Slope :

4D

Time

MSD for simulated Brownian motionDisplacement probabilities at different

times for simulated Brownian motion

EXPERIMENTAL SETUP

8

Binary imagesExperimental setup

Camera

Microfluidic Chip

250 mm

I) Experimental results

VIDEO

9

I) Experimental results

DIFFUSIVE DYNAMICS SLOWDOWN

10

Temporal evolution of the detected

number of bacteria

Bacterial transport towards the

surface via a sedimentation

process.

I) Experimental results

DIFFUSIVE DYNAMICS SLOWDOWN

11

Definition of the Mean Squared Displacement (MSD):

In the case of a Fickian behaviour:

I) Experimental results

t

DMSD 4)(

20)()( XXMSD

DIFFUSIVE DYNAMICS SLOWDOWN

12

Temporal evolution of the diffusion

coefficient

Diffusion coefficient

decreases with time

I) Experimental results

INTERMITTENT MOTILITY

13

A typical trajectory of 668s duration, divided

into run and tumble periods

I) Experimental results

Experimental displacement

probabilities

Central

part

Tails

ANALYTIC FORMULA FOR THE DIFFUSION COEFFICIENT : CONTINUOUS-TIME RANDOM WALK (CTRW) MODEL

11/15/2017 14

rt

run

tt

ll

l

runl

tt

rt

Experimental

parameters

CTRW model

parameters

2

4

1 lD

Bouchaud &

Georges, 1990

II) Model

ANALYTIC FORMULA FOR THE DIFFUSION COEFFICIENT

15/11/2017 15

II) Model

Ballistic hypothesis:

Bacteria landing

at time t’

Area covered by a

particle between t’ and t

COVERED SURFACE PROPORTION S(T)

15/11/2017 16

Bhaya, et al., 2015

Golestatnian, et al.,

2015

III) Dynamics slowdown analysis

Experimental colonisation maps drawn at different experiment times

COVERED SURFACE PROPORTION S(T)

15/11/2017 17

Glass EPS

III) Dynamics slowdown analysis

WHAT HAPPENS WITH MUTANTS ?

18

III) Dynamics slowdown analysis

Wild Type Cells

Mutant cells – Deficient in EPS production

EPSJittawuttipoka et al.,

2015

Decrease of the relative diffusion

coefficient with time

Mutants

Wild Type

COMPARISON OF DIFFERENT SURFACES

11/15/2017 19

Glass

PDMS

Temporal evolution of the diffusion coefficient on

glass and on a PDMS surface

IV) Comparison of different surfaces

SURFACE COLONISATION AFTER ONE WEEK OF CULTURE

20

Colonisation on a glass surface:

diffusion enables an homogeneized

colonisation.

Colonisation on a PDMS surface:

adhesion leads to the formation of

numerous micro-colonies.

50 mm 50 mm

IV) Comparison of different surfaces

COLONISATION AFTER ONE WEEK: MODEL

11/15/2017 21

• Numerical computations model

Speed : 2 px/step Speed : 0.05 px/step

IV) Comparison of different surfaces

CONCLUSIONS

22

o Cyanobacterium Synechocystis sp. PCC 6803 diffusive dynamics decreases with time.

o Dynamics is well described with an intermittent model.

o This decrease can be linked to a progressive surface covering with the EPS droppedby the bacteria. EPS-depleted mutants do not exhibit such a decrease.

o Early dynamics can be linked to the shape of microcolonies growing on surface.

Conclusions

ACKNOWLEDGEMENTS

Many thanks to :

o Annick Méjean

o Franck Chauvat & Corinne Cassier-Chauvat

o Mojtaba Jarrahi

o Jean-Pierre Thermeau

o Guillaume Chau, Elnaz Pashmi & Chau Minh N’guyen

23

Acknowledgements

INTERMITTENT MOTILITY

24

2))2/()2/(()(

tXtXtD

Temporal evolution of D (red) and

instantaneous speed (blue)A typical trajectory of 668s

duration

I) Experimental results

COVERED SURFACE PROPORTION S(T)

15/11/2017 25

Bhaya, et al., 2015

Golestatnian, et al.,

2015

III) Dynamics slowdown analysis

DIFFUSIVE DYNAMICS SLOWDOWN

26

Definition of the Mean Squared Displacement (MSD):

In the case of a Fickian behaviour:

I) Experimental results