Pseudomonas fluorescens:

electron micrograph of the aerobic soil bacterium Pseudomonas fluorescens
What is Pseudomonas fluorescens?

Description: Pseudomonas fluorescens is a gram negative rod shaped bacterium commonly found in decaying organic material such as leaves, soil, plants and water surfaces. It has multiple flagella that it uses for motility. As the name suggests pseudomonas fluorescens contain soluble green fluorescent pigments called pyoverdin that are produced when the iron concentration in the surrounding environment.

Growth requirements: Optimal temperatures for growth of Pseudomonas fluorescens are 25-30 degree Celsius. It is an obligate aerobe bacteria so require oxygen to survive, It is unable to grow under anaerobic conditions however some strains are capable of using nitrogen as the final electron acceptor instead of oxygen during cellular respiration.

Why is it of concern?

Pseudomonas fluorescens is a common contaminant in food. Since the optimal temperature for growth is low the bacteria can survive and multiply within refrigerators. Dairy products,eggs, meat and sea foods are commonly contaminated with P. fluorescens; it causes spoilage by producing produce enzymes such as heat stable lipases and proteases that degrade lipids and proteins in the food.

P. fluorescens has also been linked to infection in cancer patients in hospitals. Commonly infection occurs from biofilms that colonise intravenous lines. In rare cases it can cause Bacteremia, a bacterial infection of the blood. People with a normal healthy immune system are unlikely to suffer from infection. In 1997 four patients at the National Taiwan University Hospital began to suffer from symptoms including fevers and chills after being treated in the chemotherapy room . When blood was taken and analysed it was found that they had been infected by P. fluorescens.
The same kind of infection can kill immune-compromised fish such as koi carp, which are commonly kept as pets and can be very expensive.

P. fluorescens is present in a commensal relationship with plants. A commensal relationship is when one organism benefits and the other is unaffected and remains neutral. This relationship allows the plants to attain key nutrients, degrading pollutants, and suppressing pathogens via antibiotic productions.

How can P. fluorescens be used in biotechnological applications?

As stated above P. fluorescens plays an important role in plant pathogen protection. current research is being done into how to use those relationships to protect crops. There are plant pathogenic fungus such as Alternaria cajani and Curvularia lunata that grow on the plants surface and can cause the death of the plant or stunt the growth of the affected areas. The presence of the P.fluorescens stops the spore production of the fungus so it cannot grow and spread on the plants; this is being used to protect apples and pears on fruit farms from the mold that would otherwise ruin the crop. The strain that is used on the fruit farms is unable to survive above 25 degrees Celsius so it is rare to be a pathogen in the human body, it is therefore relatively safe to use around people.

In the video to the right, new research in Mexico is investigating how to use P. fluorescens to counter the effects of methyl testosterone (MT) that is being used in the fishing industry there. The hormone is given to young fish in fish farms to make them all male. The male fish grow faster and bigger than females so they make more money on the market, however, MT is escaping into the surrounding environment. When the hormone is infecting the surrounding area this can have an affect on the animals in that zone. The research is working out how to use bacteria to break down the hormone before it can affect the environment.