Bacteria are Unicellular (Single Cell) and have a range of shapes: Sphere, Rod, Spiral. They are a Few micrometers in length and will grow in a wide range of environments.

1. Basic Microbiology
and Bacterial
Metal Corrosion
Jonathan Beresford BSc (Hons) MSc
AKVO Ltd
www.akvo.co.uk

2. Bacteria

Bacteria are Unicellular (Single Cell)

Have a range of shapes: Sphere, Rod, Spiral

A Few micrometers in length

Will grow in a wide range of environments

Approximately 5x1030 bacteria on Earth

Only about half the known species of bacteria
can be grown in the laboratory

3. Bacteria



Approximately 10 times more bacteria
associated with a person than there are human
cells
The most common fatal bacterial infections are
associated with respiratory infections
TB kills around 2 million people per year in sub
Saharan Africa

4. Bacteria




Bacterial life developed around 4 billion years
ago
Multicellular organisms began to develop
around 800 million years ago
Bacteria form bio-films or bio-mats on surfaces
Bio-films can range in depth from a few
micrometers to half a meter and can be made
up of multiple bacterial species

5. Bacteria


Some bacteria can detect surrounding cells and
then move toward them (quorum sensing)
Bio-films can be very complex with different
bacteria doing different jobs e.g. form spores at
the surface to protect the film from drying out

6. Bacteria




2 general types of
bacteria:
Gram +ve and Gram -ve
Gram +ve have a thick
cell wall surrounding the
membrane
Gram -ve have a thin cell
wall surrounding the
membrane

7. Bacteria



Some Gram +ve bacteria such as Clostridium
can form spores (endospores)
When a bacteria forms and endospore it
becomes dormant. In this form it is highly
resistant to the effects of UV light, Gamma
Radiation, Disinfectants, Heat, Pressure and
Drying
Can stay dormant for thousands of years and
survive in space

8. Bacteria


Bacteria grow by cell division in a process
known as binary fission
Growth of cell numbers is exponential

9. Bacteria - Legionella

Legionella is a Gram -ve non-capsulated rod

Often found growing within amoebae

In humans they infect alveolar macrophages

Can be treated with specialist antibiotics as
growth is intra-cellular

10. Bacteria - Pseudomonas

Gram -ve rod present in water systems and
plant seeds

Motile due to flagella

Aerobic non-spore forming bacteria

Often forms bio-films

Manufacture Exopolysaccharides which cause
slime layers to be produced making them
difficult to remove

11. Bacteria - Pseudomonas



Only require a basic Carbon source for growth
and so can use a wide range of nutrients
This leads to growth in unexpected places
including in antiseptics
Common food spoilage bacteria especially in
the dairy industry

12. Bacterial Corrosion of Metals


Some species of sulphate reducing bacteria
produce hydrogen sulphide, which can lead to
sulphide stress cracking
Acidithiobacillus produce sulphuric acid

13. Bacterial Corrosion of Metals


Ferrobacillus
ferroxidans directly
oxidises Iron to Iron
Oxides and
Hydroxides
This is seen in the
“Rusticles” present on
the Titanic

14. Bacterial Corrosion of Metals




In aerobic conditions species of Thiobacillus
are the common corrosion causing bacteria
All species of Thiobacillus are relatively
common
In anaerobic conditions other species are the
main corrosion causes
They are usually spore forming sulphate
reducers

15. Bacterial Corrosion of Metals



This process requires a reducing environment with an
electrode potential of at least -100 mV
However small amounts of hydrogen sulphide can
cause these conditions in the local environment, so
once growth has started it accelerates as does the
corrosion
Several species of bacteria can be found around areas
of corrosion with some consuming the released
hydrogen causing galvanic corrosion

16. Bacterial Corrosion of Metals

Bacterial corrosion of
metals usually
appears as pitting
corrosion, however in
some cases it can
cause the metal to go
brittle by stripping the
Iron out and leaving a
graphite skeleton

17. Bacterial Corrosion of Metals



In bio-films aerobic bacteria can grow and
consume oxygen at different rates causing
varying oxygen concentrations
Two different oxygen concentrations on a
metals surface cause a difference in electrical
potential and subsequently corrosion currents
form
The area under the colony becomes anodic
and the area surrounding it cathodic

18. FOR FURTHER INFORMATION
and Corrosion Inhibition
Strategies
Contact AKVO Ltd
Tel 0844 244 8726
Or visit www.akvo.co.uk