Pseudomonas is a genus of gram negative bacteria that comprises several species. Pseudomonas fluorescens is a commonly studied strain in this bacterial group. The species name 'fluorescens' is coined with respect to its ability of secreting pyoverdin, which is a green colored, fluorescent, and soluble pigment. Responsible for contaminating food items and protecting plant diseases, this species is a topic of common interest for microbiologists all across the globe.
Based on the nature of its growth, pseudomonas fluorescens is categorized under obligate aerobes, meaning that oxygen is necessary for its survival. It prefers to grow within the temperature range of 25 - 30° C. Unlike other saccharolytic bacteria, P. fluorescens is not capable of hydrolyzing sugar for energy production. When exposed to low iron concentration, it secretes the pigment, and becomes fluorescent.
This microbe is found in decaying plant matter, living plants, soil, and water. In short, these aerobic bacteria are adaptive in different environmental conditions, and can be isolated from soil, water, and plant samples. It won't be wrong to say that this bacterium is ubiquitous in occurrence. For research purposes, pure strains are isolated and multiplied in artificial growth media (nutrient broth and nutrient agar).
Regarding the morphology, the bacterium is similar to other rod shaped species. In hydrated surfaces (foods or food processing equipment), they form bio-films, which are protected by EPS (extracellular polymeric substances). As far as genome content is concerned, this bacterium has a single chromosome, which is circular in shape. The chromosome for the strain P. fluorescens Pf-5 is made up of 7,074,893 base pairs.
The locomotive structure for this microorganism is polar flagella, which are present in multiple numbers. When chemo-attractants like sugar, organic acid, and amino acid are used in diluted concentration, this bacterium moves towards them with the help of flagella. The speed of movement, rate of change in direction (RCDI), and other motility aspects are greatly influenced by alteration in the attractant concentration.
P. fluorescens is found to be a common food contaminant, especially for dairy products and other food items, which are stored in low temperature conditions (at 4° C ). It secretes heat stable enzymes (lipase and protease), which cause souring of milk. In food supply centers, routine checkup for microbial contamination is done to maintain the food standard recommended for the particular region.
In recent times, several studies have been done based on the uses of P. fluorescens as a bio-control measure. This type of beneficial bacteria forms colonies in the plant surfaces, and provide epiphytic fitness to the host. It secretes potential antibiotics and hydrogen cyanide, which are lethal to the plant pathogens. Overall, it promotes plant growth by suppressing pathogens in the root zone, and also in the upper plant parts, helping in nutrient assimilation.
Similar to other species of pseudomonas, this bacterium is employed for treatment of environmental pollution (bioremediation). When introduced in polluted soil, it degrades plastics and other contaminating agents, thereby retaining the original soil properties. Another use of this bacterium is in commercial production of an antibiotic called mupirocin, which is effective for skin, eye, and ear infections.
It is a problematic bacterial strain in case of hospital and healthcare settings. The main reason is its resistance to common antiseptics and antibiotics that are used in medical centers. When it enters the human body, it remains asymptomatic in healthy adults; whereas it causes pseudomonas infection symptoms in children and adults, who have a weakened immune system.
Due to the significant importance of pseudomonas fluorescens in agriculture, the genome sequencing of two strains are completed. And pure strains of this microorganism are available in research institutes, which are maintained under controlled conditions for the interest of scientific studies. The future applications of this bacterium consist of employing it for bio-control use, with an aim to reduce spraying of chemical-based pest control products.