Exam 24: Nutrient Cycles, Biodegradation, and Bioremediation

Correct Answer:

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Microorganisms capable of degrading petroleum, such as certain bacteria and fungi, do not readily destroy oil tank wells and other petroleum reserves for several reasons:

1. **Anaerobic Conditions**: Many oil reserves are located in environments that lack oxygen (anaerobic conditions). The microorganisms that are most effective at degrading petroleum typically require oxygen (aerobic conditions) to metabolize the hydrocarbons efficiently. Without oxygen, their metabolic processes are significantly slowed down, or they may not be able to degrade petroleum at all.

2. **Nutrient Limitation**: The degradation of petroleum by microorganisms requires not only oxygen but also other nutrients such as nitrogen and phosphorus. In the deep subsurface environments where oil is found, these nutrients are often in limited supply, which can inhibit the growth and activity of petroleum-degrading microorganisms.

3. **Temperature and Pressure**: The high temperatures and pressures found in deep geological formations where oil is located can be inhospitable to many microorganisms. These extreme conditions can prevent the growth and activity of the microbes that would otherwise degrade the petroleum.

4. **Bioavailability**: The petroleum in oil reserves is often trapped in rock formations, making it less bioavailable to microorganisms. The oil must be in a form that is accessible for the microbes to attach to and degrade. In many cases, the oil is too deeply embedded in the rock or is present in droplets surrounded by water, which makes it difficult for the microbes to access.

5. **Inhibition by Toxic Compounds**: Crude oil contains a complex mixture of hydrocarbons, some of which are toxic to microorganisms. These toxic compounds can inhibit the growth and activity of microbes that might otherwise degrade the oil.

6. **Slow Metabolic Rates**: Even when microorganisms are present in oil reserves, their metabolic rates can be very slow due to the suboptimal conditions. This slow metabolism means that any degradation of petroleum that does occur happens over geological timescales, which is much slower than the rate at which humans extract and use petroleum.

7. **Human Intervention**: Oil tank wells and other infrastructure are designed to prevent microbial contamination and degradation. Measures such as the use of biocides, regular maintenance, and the construction of physical barriers help to protect petroleum reserves from microbial attack.

In summary, the combination of harsh environmental conditions, lack of necessary nutrients, and human interventions all contribute to the preservation of oil tank wells and other petroleum reserves from degradation by microorganisms.