Forms of Metallic Corrosion
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the case of metal corrosion caused by sulfate-reducing bacteria (SRB), the
accompanying organisms remove oxygen and produce simple carbon compounds, such as acetic acid and/or lactic acid, as nutrients for SRB.
Bacteria are the smallest living organisms on this planet. Some can only
live with, and others only without oxygen. Some can adapt to changing conditions and live with either, aerobically or anaerobically. There is wide diversity with regard to their metabolisms. They are classified as to their source
of metabolic energy as follows:
Energy Source
Classification
Light
Phototrophs
Chemical reactors
Chemotrophs
Inorganic hydrogen donators
Lithotrophs
Organic hydrogen donators
Organotrophs
Carbon dioxide (cell source)
Autotrophs
Organic molecules (cell source)
Heterotrophs
These six terms may be combined to easily describe the nutritional requirements of bacteria. For example, if energy is derived from inorganic hydrogen
donators and biomass are derived from organic molecules, they are microtrophs (chemo-litho-organotrophs).
An important feature of microbial life is the ability to degrade any naturally occurring compound. Exceptions to the rule are a few manmade materials such as highly polymerized and halogenated compounds.
In addition to energy and carbon sources, nitrogen, phosphorus, and trace
elements are needed by microorganisms. Nitrogen compounds may be inorganic ammonium nitrate as well as organically bound nitrogen (e.g., amino
acids, nucleotides). With the help of an enzyme called nitrogenase, bacteria
are able to fix nitrogen from atmospheric nitrogen, producing ammonia that
is incorporated into cell constituents.
Phosphorus is taken in as inorganic phosphate or as organically bound
phosphoroxylated compounds such as phosphorus-containing sugars and
liquids. Phosphorus, in the form of adenosine triphosphate (ATP), is the
main energy-storing compound.
For many of the metabolic purposes, trace elements are needed. Cobalt
aids in the transfer of methyl groups from/to organic or inorganic molecules.
Vitamin B 12 , cobalamin, is involved in the methylation of heavy metals such
as mercury. Iron, as Fe 2+ or Fe 3+ , is required for the electron transport system, where it acts as an oxidizable/reducible central atom in cytochrome of
nonhemo-iron-sulfur proteins. Magnesium acts in a similar manner in the
chlorophyll molecule. Copper is an essential part of a cytochrome that, at the
terminal end of the electron transport system, is responsible for the reduction of oxygen to water.
51
the case of metal corrosion caused by sulfate-reducing bacteria (SRB), the
accompanying organisms remove oxygen and produce simple carbon compounds, such as acetic acid and/or lactic acid, as nutrients for SRB.
Bacteria are the smallest living organisms on this planet. Some can only
live with, and others only without oxygen. Some can adapt to changing conditions and live with either, aerobically or anaerobically. There is wide diversity with regard to their metabolisms. They are classified as to their source
of metabolic energy as follows:
Energy Source
Classification
Light
Phototrophs
Chemical reactors
Chemotrophs
Inorganic hydrogen donators
Lithotrophs
Organic hydrogen donators
Organotrophs
Carbon dioxide (cell source)
Autotrophs
Organic molecules (cell source)
Heterotrophs
These six terms may be combined to easily describe the nutritional requirements of bacteria. For example, if energy is derived from inorganic hydrogen
donators and biomass are derived from organic molecules, they are microtrophs (chemo-litho-organotrophs).
An important feature of microbial life is the ability to degrade any naturally occurring compound. Exceptions to the rule are a few manmade materials such as highly polymerized and halogenated compounds.
In addition to energy and carbon sources, nitrogen, phosphorus, and trace
elements are needed by microorganisms. Nitrogen compounds may be inorganic ammonium nitrate as well as organically bound nitrogen (e.g., amino
acids, nucleotides). With the help of an enzyme called nitrogenase, bacteria
are able to fix nitrogen from atmospheric nitrogen, producing ammonia that
is incorporated into cell constituents.
Phosphorus is taken in as inorganic phosphate or as organically bound
phosphoroxylated compounds such as phosphorus-containing sugars and
liquids. Phosphorus, in the form of adenosine triphosphate (ATP), is the
main energy-storing compound.
For many of the metabolic purposes, trace elements are needed. Cobalt
aids in the transfer of methyl groups from/to organic or inorganic molecules.
Vitamin B 12 , cobalamin, is involved in the methylation of heavy metals such
as mercury. Iron, as Fe 2+ or Fe 3+ , is required for the electron transport system, where it acts as an oxidizable/reducible central atom in cytochrome of
nonhemo-iron-sulfur proteins. Magnesium acts in a similar manner in the
chlorophyll molecule. Copper is an essential part of a cytochrome that, at the
terminal end of the electron transport system, is responsible for the reduction of oxygen to water.