How Fuel Bugs Operate

Contaminated and impacted fuel has as much to do with microbiology as it does chemistry.

Environmentalists, when cleaning up soils from contaminated areas, often apply "bioremediation", which is the breaking down of fuel (hydrocarbons) by the use of specialized bacteria and fungi. As an army of ants strip bare a carcass so these microbes break up the chemical elements of fuel.

Fuel bugs are extremely efficient in breaking down complex constituents into basic elements. It is not surprising that a cubic meter air sample may contain thousands of differing species of fungi and many millions of individual spores. (Fungi of the genus Cladosporium (right) continuously produce multitudes of spores from their conidiophore, (the stems upon which the spores grow)).

With a diameter in the range of just 0.5-20µm and a miniscule mass, spores are carried by the slightest breeze and can remain suspended in still air for long periods of time. In ideal conditions some spores can remain "alive" for hundreds of years. The minute spore represents the simplest and most successful means by which both simple and complex organisms are able to dissipate and reproduce.

A spore ending up in the most unlikely of places has a good chance of germinating if it comes across nutrition or the by-products of already entrenched microbes - provided that initially there is moisture present. The hardy little spore is assisted by microcosms through which symbiotic relationships between the many differing types of microorganisms flourish in even the harshest of environments.

The level of chemical re-engineering that can take place in these organisms is considerable. The altered by-products result from processes principally employed to satisfy the organisms' needs. The aerobic groups of yeasts, fungi and bacteria initially utilise oxygen in the stripping down of complex compounds into basic compounds using an exothermic process that is characterised by the production of heat and new chemicals.


The oxidative process employed by the fungi cladosporium resinae in a diesel environment yields carbon dioxide, water and energy, as represented in the sequence opposite.

The oxidative process employed by sulphur denuding bacteria yields water, sulphur and energy. Other sulphur-dependant bacteria reprocess the sulphur, in turn yielding sulphuric acid and energy in the sequences:



These sequences simplify the manner in which microbes act in breaking down fuels, however there are many other by-products and processes that continue well beyond the scope of this reference.

If water is the most common form of fuel contamination then microbes are literally the second most common form of fuel contamination. The presence of water in fuel appears to trigger the ever-present spores into germination, resulting in the breakdown of their food source (fuel). Microbes do this by congregating at the point at which fuel and water meet. This position allows the spores to attack the fuel-food source while utilising the available oxygen dissolved in water. Specific organisms will attack various fuel components, producing alternate basal compounds that other organisms will absorb. Paradoxically fuel will remain unaffected by microbial attack for long periods when there is no water present.


A few spores of Cladosporium resinae (as pictured above left) will quickly grow into a substantial colony. Although microscopic, the fungal filaments will grow into a dense mat at the point where fuel meets water. (The photograph above right, taken inside an 'infested' underground fuel storage tank, shows the mat left behind after the fuel stock has been pumped off and the water body pumped from below the mat). Cladosporium resinae usually precedes the organisms that feed off the byproducts that it produces when breaking down the fuel-food source. The fungi breaks down stable compounds such as the benzene ring structures of fuel to simpler linear hydrocarbons that can then be broken up further by Pseudomona (bacteria) species. Collectively, the microbes will over time greatly impair the ignition characteristics of fuel.

The consequences of fuel contaminated by both water and microbial activity can be significant in terms of fuel containment and vehicular performance. The 'sulphur-dependant' bacteria excrete sulphides that, when mixed with water, produce the corrosive compound sulphuric acid. This acid attacks the metal shell of fuel tanks from the inside. Cladosporium resinae produces a bio-surfactant that degrades fuel by allowing water to partially mix with it, creating an emulsion which affects the combustive qualities of the fuel, thus impacting the performance characteristics of the motor and increasing fuel consumption.

Large amounts of fungal material have been found as far 'up stream' of a fuel tank as the fuel pump where there has been sufficient moisture in the system (water saturated fuel) to support the breakdown of fuel. Large displacement motors that combust water-saturated fuel usually demonstrate startability problems, filter blockage, heavy exhaust emissions and higher than usual consumption with corresponding loss of net power.

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