Brent Cornell

    
A pollutant is a substance introduced into the environment that has an adverse effect upon a natural resource

• Certain pollutants may be disintegrated via the biological metabolism of microorganisms (biodegradation)

Examples of pollutants that may be metabolised by microorganisms include:

• Oil:  Hydrocarbons in crude oil may be metabolised by Pseudomonas
• Benzene:  Aromatic hydrocarbons (e.g. benzene) may be metabolised by halophilic Marinobacter
• Mercury:  Toxic methyl mercury may be converted into environmental mercury by Pseudomonas
• Uranium:  Uranium can be converted by Geobacter sulfureducens into a insoluble form that can be easily collected

    
Oil Spills

Crude oil is a non-uniform material composed of a mixture of hydrocarbons in variable proportions

• It can be processed to form petroleum products that can be refined to form various types of fuels (e.g. gasoline, etc.)
• When crude oil is released from containment (i.e. via damaged tankers or pipelines), it will form a floating slick on water

Crude oil is biodegradable and hence oil spills are commonly dispersed by bacterial decomposition (bioremediation)

• Physical procedures (such as the surface pumping of an oil slick) are highly laborious, expensive and slow
• Chemical procedures (such as the use of dispersants) may be non-biodegradable and toxic to marine ecosystems 

Pseudomonas is a chemoheterotroph that can utilise crude oil as its sole carbon source, making it efficient at oil degradation

• The hydrocarbons within the oil are converted into biomass or broken down via respiration into carbon dioxide and water
• Spraying the oil with essential inorganic nutrients (e.g. nitrates, phosphates, etc.) assists in the conversion to biomass
• The efficiency of oil degradation can also be improved by the presence of a surfactant (helps distribute the bacteria)

A high presence of salt at an oil spill may inhibit bacterial species (such as Pseudomonas) from being able to degrade the oil

• Oil spills commonly occur in marine environments – oil is frequently extracted in off-shore locations and transported by ship
• Additionally, the extraction of oil from underground reserviors is often accompanied by brine (salt water)

Marinobacter are a halophilic ('salt-loving’) bacteria that can degrade certain hydrocarbons present in crude oil (i.e. benzene)

• Whilst not as efficient at degrading oil as Pseudomonas, its tolerance for salt environments makes it a useful alternative

Hydrocarbon Metabolism by Chemoheterotrophs

    
Mercury Contamination

Mercury exists in three forms: as a metal (elemental mercury), as inorganic ions or as an organic form (methyl mercury)

• Elemental mercury is produced as an industrial pollutant and is converted to the other forms by aquatic bacterial communities

Methyl mercury is the most toxic form and will accumulate within aquatic ecosystems polluted by elemental mercury

• Pseudomonas is capable of degrading the toxic methyl mercury to form elemental mercury and methane gas
• This makes Pseudomonas an important biological agent in the treatment and remediation of mercury pollution

Mercury Conversion