Copy Of Pseudomonas And The Pseudomonads

PSEUDOMONAS AND THE PSEUDOMONADS

CHARACTERISTICS

OF

PSEUDOMONADS

Pseudomonads have very simple nutritional requirements and grow chemoorganotrophically at neutral pH and at temperatures in the mesophilic range. One of the striking properties of pseudomonads is their ability to use many different organic compounds as carbon and energy sources. Some species utilize over 100 different compounds, and only a few species utilize fewer than 20. • As an example of this versatility, a single strain of Burkholderia cepacia can use many different sugars, fatty acids, dicarboxylic acids, tricarboxylic acids, alcohols, polyalcohols, glycols, aromatic compounds, amino acids and amines, plus miscellaneous organic compounds not fitting into any of these categories. • On the other hand, pseudomonads generally lack the hydrolytic enzymes necessary to break down polymers into their component monomers. These nutritionally versatile pseudomonads contain numerous inducible operons (Section 9.3) because the catabolism of unusual organic substrates often requires the activity of several different enzymes. The pseudomonads are ecologically important organisms in soil and water and are probably responsible for the degradation of many soluble compounds derived from the breakdown of plant and animal materials in oxic habitats. They are also capable of breaking down many xenobiotic (not naturally occurring) compounds, such as pesticides and other toxic chemicals, and are thus important agents of bioremediation in the environment. Most pseudomonads metabolize glucose via the Entner–Doudoroff pathway, a variation of the glycolytic pathway in which early steps in glucose catabolism differ from the glycolytic pattern . • A survey for the presence of the Entner–Doudoroff pathway has shown it to be absent from gram-positive Bacteria but present in bacteria of the genera Pseudomonas, Rhizobium, Agrobacterium, Zymomonas, and several other gram-negative Bacteria.

PATHOGENIC

PSEUDOMONADS

A number of pseudomonads are pathogenic • Among the fluorescent pseudomonads, the species Pseudomonas aeruginosa is frequently associated with infections of the urinary and respiratory tracts in humans. • P. aeruginosa infections are also common in patients receiving treatment for severe burns or other traumatic skin damage and in people suffering from cystic fibrosis. P. aeruginosa is not an obligate pathogen. • Instead, the organism is an opportunist, initiating infections in individuals whose resistance is low. In addition to urinary tract infections, it can also cause systemic infections, usually in individuals who have experienced extensive skin damage. • Other pseudomonads are also human pathogens, such as Burkholderia cepacia, which like P. aeruginosa can infect the lungs of patients with cystic fibrosis. P. aeruginosa is naturally resistant to many of the widely used antibiotics, so chemotherapy is often difficult. Resistance is due to a resistance transfer plasmid (R plasmid) which is a plasmid carrying genes encoding proteins that detoxify various antibiotics, and to the presence of multidrug efflux systems that pump antibiotics out of the cell . • P. aeruginosa is commonly found in the hospital environment and can easily infect patients receiving treatment for other illnesses.. Polymyxin, an antibiotic not ordinarily used in human therapy because of its toxicity, is effective against P. aeruginosa and is used in certain medical situations. • Certain species of Pseudomonas, Ralstonia, and Burkholderia and the genus Xanthomonas are well-known plant pathogens (phytopathogens). In many cases these organisms are so highly adapted to the plant environment that they are rarely isolated from other habitats, including soil.