Pseudomonas aeruginosa
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Classification
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The genus Pseudomonas holds about sixty different types of species in the kingdom classified as bacteria. The species Pseudomonas aeruginosa is classified as a gram-negative bacterium[1]|. Most Pseudomonas aeruginosa are categorized as obligate aerobes, however sometimes in certain environmental conditions, the bacteria acts as a facultative anaerobe. Furthermore, because of the way it obtains its energy, it is considered to be a chemoheterotroph. (Willey)
Description and significance
The Pseudomonas genus includes bacteria that are straight or slightly curved rods. P. aeruginosa is a rod-shaped bacterium. Its size ranges from 0.5 to 1.0mm by 1.5 to 5.0mm in terms of its length and width. Almost all types of strains are motile by means of a polar flagellum (Todar). P. aeruginosa is a well-studied species due to its high level pathogenicity and its significant role in human disease. The organism can affect humans, animals as well as plants, and can thrive under many environmental conditions, such as in soil, water and even hospital environments. P. aeruginosa is primarily a nosocomial pathogen. According to the CDC (Center for Disease Control), the overall incidence of P. aeruginosa infections in U.S. hospitals averages about 0.4 percent (4 per 1000 discharges), and the bacterium is the fourth most commonly-isolated nosocomial pathogen accounting for 10.1 percent of all hospital-acquired infections (Todar).
Gene mapping studies of Pseudomonas aeruginosa have helped researchers and clinicians better understand local gene expression and the evolution of Pseudomonas aeruginosa as it has adapted to the CF lung. Because of its ability to resist many antibiotics and due to its high level of adaptability to most environments, p. aeruginosa genome sequencing proved to be crucial.
Describe how and where it was isolated.
Genome structure
Pseudomonas aeruginosa is the largest of the 25 bacteria that scientists have sequenced so far [3]. The genome of P. aeruginosa has an unusually large number of genes for nutrient transport, metabolic regulation and catabolism; this may be why the bacterium has the ability to grow in a wide range of environments and resist antibiotics (Willey). This microbe’s genome is a single circular chromosome that is made up of 6,264,403 base pairs (Bp), which is 6.3 million bases (Mb) and contains 5,570 predicted genes on one chromosome (Stover, et al). The P. aeruginosa almost the largest genome sequenced as compared to other bacterial genomes that have been sequenced. Due to its large genome size, P. aeruginosa has tremendous genetic density, allowing it to form biofilms. It utilizes quorum sensing (group symbiosis) to achieve its resistance against microbial agents in most cases. They also have metabolic plasmids that are about 75-230 kbp in size and are involved in degrading substances such as sugars.
Describe the size and content of the genome. Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?
Cell structure and metabolism
The P. aeruginosa has a cell wall that is gram-negative as it is composed of three layers; the plasma membrane, a thin peptidoglycan layer, and an outer membrane. Since P. aeruginosa is a chemoheterotroph, it can grow on the least amount of media available to them and will use just about anything as their carbon source to build up their biofilm in various types of environments (Willey, et al 2008).
[biofilm]
Gram-negative bacterium generally have seven different pathways of protein secretions, and three of them are seen in P. aeruginosa. These protein secretion pathways include ABC transport proteins that are embedded in lipid membranes, and are involved in the translocation of many different substrates across the membrane.
P. aeruginosa secretes virulence factors which include potent toxins and degradative enzymes. The toxins cause extensive tissue damage and also interfere with the human immune systems defense mechanisms. They also enter and kill host cells at or near the site of colonization. Moreover, the bacterium's degradative enzymes permanently disrupt the cell membranes and connective tissues in various organs; these enzymes include lipases and proteases [3].
P. aeruginosa is ubiquitous in soil and water, and on surfaces in contact with soil or water. Its metabolism is respiratory and never fermentative, but it is able to grow in the absence of O2 if NO3 is available as a terminal electron acceptor (Todar).
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Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
P. aeruginosa can infect animals, plants and also humans. They cause disease in humans who are already ill, infecting those patients with low resistance in their bodies. P. aeruginosa are opportunistic pathogens and cause infection in patients who are diagnosed with cystic fibrosis, have lower respiratory tract infections, surgical wounds, urinary tract infections, skin infections i.e:(dermatitis), and even in patients who have cancer i.e: blood cancer (Willey). It causes nosocomial infection in patients as this bacterium can grow anywhere where enough nutrients and enough moisture are found.
An opportunistic pathogen, P. aeruginosa produces a thick biofilm and due to its dense colonization, it is able to resist many antibiotics, disinfectants, as well as UV light and infected patients can therefore be difficult very to treat. Another factor that contributes to P. aeruginosa resistance is its gram negative cell wall that is composed of three layers; the inner plasma membrane, peptidoglycan, and its outer membrane. This high level of resistance in P. aeruginosa can be of consequence and dangerous to a patient’s health.
The bacterium is naturally resistant to many antibiotics due to the permeabiliity barrier afforded by its Gram-negative outer membrane. Also, its tendency to colonize surfaces in a biofilm form makes the cells even more resistant to antibiotics. Moreover, Pseudomonas maintains antibiotic resistance plasmids, R-factors and RTFs, and it is able to transfer these genes by horizontal gene transfer (HGT), mainly transduction and conjugation (Todar).
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
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References
Willey, Sherwood, Woolverton. 2008. Prescott, Harley, and Klein’s Microbiology, Seventh Edition. New York 10020: McGraw-Hill Companies, Inc. 1088p.
Todar, Kenneth: Pseudomonas aeruginosa. [2] University of Wisconsin-Madison Department of Bacteriology.
[3] Pseudomonas aeruginosa