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:: Section 3 of 10

Viable Bioaerosols: Microbiological Focus

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Prokaryotes are single cellular organisms and are one of the simplest living organisms known to humans. One of the most distinguishing factors about prokaryotes is the lack of a nucleus. The DNA of prokaryotes exists only as a single, circular molecular strand within the cell. The most prevalent form of prokaryotes is the bacterium. Bacteria are generally about 0.3-100 micrometers in diameter and occur at a natural concentration of 0.5-1000 airborne bacteria per cubic meter of ambient air.

A schematic of a prokaryotic cell is shown in the figure below. Note its simplicity.

Figure 4: Schematic of a prokaryotic cell.2

Although most bacteria are harmless and many are even beneficial, some bacteria do cause disease. Infamous pathogenic bacteria include: Mycobacterium tuberculosis (causes tuberculosis), Legionnella pneumophila (responsible for a type of pneumonia known as Legionnaires' diesease), Bacillus anthracis (responsible for Anthrax), and Yersinia pestis (responsible for pneumonic plague). Antibiotics can disrupt important parts of the cell, such as the cell wall, cytoplasmic membrane, and protein synthesis. By doing so, the bacteria is either killed or inhibited, making the antibiotic effective for treating bacterial infections.

Some bacteria can release spores which are very resiliant to adverse conditions and are thus able to survive for extended periods until more preferable conditions are available. Bacillus anthracis has this characteristic, which contributes to its potency as a potential agent of biological warfare.

For more information on the components of the prokaryotic cell, please check out

2Figure courtesy of Tim Sheppard,, What is a cell?