The bacterium Pseudomonas aeruginosa is found naturally in soils, in water, and on plants. It is also found on surfaces in hospitals and homes.

Early classifications named it as Bacterium aeruginosum, Pseudomonas pyocyana, Pseudomonas pyocyanea, Pseudomonas polycolor, Pseudomonas vendrelli, among others. It was classified by Schroeter in 1872

Like many bacteria, P. aeruginosa is a single cell rod shaped organism that has a flagellum, fimbriae, and at least one pilus.

The flagellum is used to propel the bacterium around or to anchor it to a substrate or other P aeruginosa cells. The fimbriae are also used to attach the bacteria to other cells, a surface, and to each other. The pili are used to connect to and exchange genetic material with another P. aeruginosa, a process called lateral or horizontal gene transfer.

It is classified as a gram-negative bacterium, the type that is most often pathogenic to humans. Using the pili, P. aeruginosa can rapidly exchange DNA in the colony of bacteria, which in part explains P. aeruginosa’s rapid development of multi-drug resistance.

Metabolically, P. aeruginosa is chemoheterotrophic generally aerobic utilizing a wide range of organic compounds for sources of carbon and nitrogen.

In nature P. aeruginosa naturally grows as a planktonic form of single cell organisms dispersed and motile within the medium that it is growing such as soil or water. In motile form, research has found P. aeruginosa to be among the speed demons of the bacteria world. It does not form spores.

Under ideal conditions, P. aeruginosa uses its flagellum and/or fimbriae to anchor itself and possibly to each other on a surface to produce a growing mat of bacteria cells. The bacteria growing together in this manner called abiofilm and may have developed evolutionally as a protection mechanism. The rhamnolipids help form a protective cover for the mat of the P. aeruginosa bacteria.

These biofilms are both useful and problematic to mankind.

Bacterium Pseudomonas aeruginosa, like many gram-negative bacteria, is a pathogen and can make people sick in sufficient quantities. When it forms a biofilm it is very difficult to treat with antibiotics. Although found almost everywhere, it is a significant cause of nosocomial infections where adaptive resistance to antibiotics is occurring, accounting for over 10% of hospital acquired infections.

P. aeruginosa has been implicated in infecting immune compromised individuals and specific infections related to lung infections associated with cystic fibrosis, corneal disease, burns wounds, urinary tract, hot tub rash, ear, and other organs. It is considered an opportunistic pathogen because while it is all around, it does not infect unless the target has a wound or isimmunocompromised. An infection usually produces a mild odor of grapes and bluish-green pus.

There are a large number of strains of P. aeruginosa. There are over 100 strains of P. aeruginosa on file at the American Type Culture Collection (ATCC). There are also a number of strains that are unavailable though ATCC such as the collection developed over many years and now owned by Rhamnolipid, Inc. Additionally there are probably thousands of strains isolated by various research institutions around the world. Some work has gone into typing them into groups, but the task is huge and there seem to be a very large number of types. Each strain has different characteristics including how much rhamnolipid is produced, which types of rhamnolipids are produced, what it metabolizes, and conditions in which it grows. Only a small percentage of the strains have been extensively studied.

Through evaluation and selection, strains of P. aeruginosa can be isolated to produce rhamnolipids at higher concentrations and more efficiently. Strains can also be selected to produce less byproduct and to metabolize different feedstock or pollutants. This production is greatly affected by the environment in which the bacterium is grown.

Pseudomonas aeruginosa, like other Pseudomonas species, metabolize carbon source such as fats and oils. In addition to being found in soils, water, and on plants, P aeruginosa can be found in sources of oil such as seeps, spills, leaks, and in oil being transported. They can survive in both aerobic and some anaerobic environments in a wide range of pH and temperatures.

P. aeruginosa is one of the most studied bacteria due to common occurrence in nature and pathogenic properties. One strain of P. aeruginosa, PAO1, had its complete genome sequenced as early as 2000.