Physical chemistry of bacterial leaching

1
Physical chemistry of bacterial leaching

• Lecture no.3

2
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

3
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

4
Steps in the colonization of the mineral surface
5
Theory of adhesion
6
The contact angle
The adhesion of bacteria to the
polystyrene surface was strongly correlated with
the contact angle
7
Young equation
Thomas Young proposed the equation for a drop of
liquid placed on a solid surface
8
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 2v??-

9
Surface energy and hydrophobicity
10
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

11
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.

12
Attraction energy

• The attraction energy VA arising from the van der
  Waals force between colloidal particles of radius
  r and separated by a distance H, is given
• where A123 is the Hamaker constant of the
  system.
• The Hamaker constant can be calculated from
  contact angle by a method outlined by Fowkes

13
Interaction energy curve
14
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.

15
Double electric layer
16
Schematic diagram of the electric double layer
17
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.
18
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
• VTOT VA VE AAB
• 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.

19
DLVO theory curves
20
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).
21
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 220C under the
  required pH.
• Bacteria cells were dispersed in 10-2 M KCl,
• The cell concentration was 3 x 108 cells/ml

22
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
23
Adhesion of bacteria cells
The relationship between the contact angel of the
bacterial cell and zeta potential. Results for
adhesion of bacteria
24
Adhesion of Bacillus suptilis onto the calcite
surface
25
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.

26
Attachment side

• AFM imges demonstrate that cells of
  A.ferrooxidans preferentially attach to sites
  with visible surface imperfections.

27
Atomic Force Microscope
28
Atomic Force Microscope (AFM)
29
AFM image
30
AFM image
Pyrite surface after 24 h of incubation with A.
ferrooxidans Cells attached preferentially to the
sites with surface defects
31
AFM-imige of cells of Leptospirillum ferrooxidans
attached to pyrite after 24h of incubation
32
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).
33
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
34
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