Pseudomonas aeruginosa

Pseudomonas aeruginosa is a highly adaptable bacterium that plays a major role in medicine and the environment.

It is a rod-shaped, Gram-negative organism that is classified as a facultative anaerobe. This means it can thrive in environments with plenty of oxygen or in places where oxygen is nearly absent. The bacterium is found globally in soil, water, and human skin. It is also common in many human-made environments. Because it is so widespread and can cause serious illness, it is a major focus for scientists and doctors.

The bacterium uses several complex mechanisms to survive in diverse habitats. To grow, it requires nutrients like iron, which is often difficult to find in an accessible form. P. aeruginosa secretes molecules called siderophores to bind and transport iron into the cell. This process involves a social dynamic between different members of the bacterial population. Some bacteria act as cooperators by producing these siderophores for the group. Others act as cheaters by using the iron without spending energy to make the molecules.

In terms of its biology, P. aeruginosa has a large and complex genome. It possesses a circular chromosome that is between 5.5 and 6.8 million base pairs in size. This genome contains between 5,500 and 6,000 open reading frames, which are the parts of the DNA that provide instructions for making proteins. A 2020 study analyzed 494 different Pseudomonas genomes to understand their diversity. Researchers found that while they share a core genome, the species is surprisingly diverse. Industrial strains often have the largest genomes, while clinical isolates tend to be smaller.

One of the most significant traits of P. aeruginosa is its ability to resist antibiotics. The World Health Organization identifies it as a major threat due to this multidrug resistance. The bacterium uses advanced mechanisms to protect itself from medicine. It can selectively block antibiotics from entering through its outer membrane. It also uses efflux systems to pump drugs out of the cell. Additionally, it produces enzymes called beta-lactamases that can break down certain antibiotics. These traits make treating infections very difficult and sometimes require advanced drug regimens.

This bacterium is considered an opportunistic pathogen, meaning it often infects people who are already ill. It is especially dangerous for those who are immunocompromised, or have weakened immune systems. For example, it can cause serious lung infections in patients with cystic fibrosis. In these patients, the bacteria can form thick layers called biofilms. These biofilms consist of bacterial cells surrounded by a protective material called alginate. These structures protect the bacteria from the immune system and make them very hard to kill.

In addition to medical concerns, P. aeruginosa has unique physical characteristics. It produces a distinct, sweet odor that smells like grapes. This smell comes from the synthesis of a chemical called 2-aminoacetophenone. The bacterium also produces colorful pigments that are visible in laboratory cultures. It creates a blue pigment called pyocyanin and a green pigment called pyoverdine. These two metabolites combine to give the cultures a characteristic blue-green color.

Beyond its role in disease, P. aeruginosa shows remarkable versatility in the environment. It is capable of decomposing hydrocarbons, which are organic compounds found in many substances. This ability allows the bacterium to help break down tarballs and oil from large oil spills. This makes it a useful organism for cleaning up certain types of environmental pollution. Its ability to live in many different settings, from hospital equipment to deep ocean oil, shows how successful this species is at adapting to the world around it.