Physical chemistry of

bacterial leaching

Lecture no.3

Cell adhesion

• Adhesion of microorganisms to the

mineral surface is ever present in the

natural environment.

• Microbial adhesion occurs and is

detrimental in wide range of areas

such as:

Biocorrosion
Biofouling
Bioleaching

Bacteria attachment

• The attachment of bacteria to the

mineral surface is affected by
hydrophobic and electrostatic
parameters.

• The

surface chemistry

of bacteria

attachment.

• The colonization of a surface by

bacteria is occurring in four distinct
steps

Steps in the colonization of

the mineral surface

Theory of adhesion

The contact angle

The adhesion of bacteria to the polystyrene

surface was strongly

correlated with the contact angle

Young equation

Thomas Young proposed the equation
for a drop of liquid placed on a solid
surface

Surface energy

1.Fowkes pioneered the surface component

approach He divided the total surface energy

in 2 parts.

= 

d

+ 

p



d

– dispersive part (Londona- van der Waalsa)



p

- non-dispersive part – polar part

2. Van Oss and Good diveted polar component of

surface energy into electron accepting (



+

)

and

electro-donating (



-

) parameters.

= 

VdW

+ 

AB



AB

= 2√

+



-

Surface energy and

hydrophobicity

Contact angle Hydrophobicit

y

Surface

energy

0

0

- 90

0

hydrophilic

High

(up to 100 mJ)

90

0

- 180

0

hydrophobic

low

(10- 30mJ)

Bacteria cell as colloid

particle

• Bacteria in solution have been

frequently described as colloidal
suspension.

• The colloid particles interaction is the

combination of attraction and repulsion
forces.

• Attraction force

– van der Waals force

• Repulsion force

– electrostatic force

Van der Waals force

• Van der Waals force is responsible for

long-range

attractive forces

between

colloid particles and between colloid

particle and the surface.

• Hydrophobicity arises when the

magnitude of van der Waals

interaction between water molecules

is greater

than the interactions of the

water molecules and the surface.

Attraction energy

• The

attraction energy V

A

arising from the van

der Waals force between colloidal particles of

radius r and separated by a distance H, is

given:

where: A

123

is the Hamaker constant of the

system.
The Hamaker constant can be calculated from

contact angle by a method outlined by Fowkes

H

r

A

V

A

6

132





Interaction energy curve

Electrostatic force

• The electrostatic forces are generally

repulsive in bacteria surface
interaction.

• The electrostatic forces arise

because both the colloid particles
and surface are charged.

Double electric layer

Schematic diagram of the

electric double layer

Surface potential of e.d.l.

The surface
potential of e.d.l
cannot be directly
measured

The zeta potential
represents the
potential between
the plane of shear
and the bulk
solution.

Theory of D.L.V.O.

(Derjaguin, Landau, Verwey,

Ovrbeek)

• The total interaction energy is presented

as a function of the distance of separation.

• Total interaction energy is given by:

V

TOT

= V

A

+ V

E

+ A

AB

• Initial bacterial adhesion can be described

by the DLVO theory in which adhesion is

predicted as interplay of Lifshitz-van der

Waals interaction, electrostatic

interactions and Lewis acid –base

interactions.

DLVO theory curves

Bacterial adhesion to solid

surfaces – disjoining pressure

The interplay between electrostatic forces and attractive van der
Waals surface forces and the charge of the bacterium cell determines
the minimum approach distance (position of the energy barrier/well).
Most bacteria in soils are negatively charged (otherwise, immobile).

Electrokinetic behavior of bacteria

cells

• Zeta potential of unadapted and

adapted A. ferrooxidans cells were
determined using a Zeta-meter.

• The tests were carried out at 22

0

C

under the required pH.

• Bacteria cells were dispersed in 10

-2

M

KCl,

• The cell concentration was 3 x 10

8

cells/ml

Zeta potential

(a) pyrite, (b) chalcopyrite-after interaction

with

A. ferrooxidans

Square-mineral alone

Circle-mineral interacted with ferrous grown cells

Triangle-mineral interacted with sulfur grow cells

Adhesion of bacteria cells

pokrycie, %

kąt zwilżania, 

potencjał

dzeta, mV

100

75

50

25

0

60

40

20

-30

-20

-10

0

The relationship between the contact angel of the
bacterial cell and zeta potential. Results for adhesion of
bacteria

Adhesion of Bacillus suptilis onto the

calcite surface

Biofilm (EPS)

• Most bacteria grow attached to

mineral surface in form of a biofilm.

• Bacterial attachment predominantly

is mediated by EPS (biopolymers),
which surround the bacterial cells.

• Bacteria are able to adapt their EPS

(biopolymer) according to the solid
surface.

Attachment side

• AFM imges demonstrate that cells of

A.ferrooxidans preferentially attach
to sites with visible surface
imperfections.

A

tomic

F

orce

M

icroscope

Atomic Force Microscope

(AFM)

AFM image

AFM image

Pyrite surface after 24 h of incubation with A.
ferrooxidans

Cells attached preferentially to the sites with surface
defects

AFM-imige of cells of Leptospirillum

ferrooxidans attached to pyrite after

24h of incubation

Cell of A.ferrooxidans attached to

the pyrite surface

Electron coming from pyrite to the iron(III) complex at
EPS and iron(III) is reduced to iron(II).

Adhesion of A.ferrooxidans

cells onto the mineral surface

red-pyrite; blue-chalcopyrite; green-sphalerite;
yellow-galena;
yellow cross-quartz

A-strain R-1 and B-strain SPm/3

Summary

• The cells of leaching bacteria are

attracted to the mineral surface by
van der Waals force.

• EPS generate microenvironment for

bacteria cells attached to the mineral
surface