Introduction

The species which make up the genera Pseudomonas are a diverse and ecologically important group of microorganisms. Member of the family Pseudomoadacea, Pseudomonas can be found primarily in the soil and water. There are a great number of Pseudomonas species which have been characterized, however the exact phylogenetic relationships of these species is not completely understood. Currently, the Pseudomonas genus is divided into five groups on the basis of ribosomal RNA similarity, however, the use of this system is presently under debate. All Pseudomonas species are Gram-negative, rod-shaped bacteria, and test positive for oxidase. Almost all species are also motile with at least one polar flagella.

The diversity of the members of this genus cannot be underestimated. There are Pseudomonas species that are considered ubiquitous in soil, while there are also those which live only as a pathogen of a specific plant. Species of Pseudomonas can also be found in fresh and salt water, in spoiling food and as opportunistic animal pathogens. Only one species, however, is considered to be an obligate animal pathogen.

One cause of this niche diversity is the ability of many Pseudomonas species to grow well on very minimal media and in mixed populations with other microorganisms. Furthermore, Pseudomonas is able to grow on a wide range of organic materials particularly low-molecular-weight compounds. As a result, some Pseudomonas species seem to have developed a mutualistic relationship with microorganisms of the genus Streptomyces, an organism good at degrading high-molecular-weight compounds. This relationship is further aided by some Pseudomonas' development of resistance to antibiotics produced by Streptomyces, and further their ability to spread this resistance through a population by the transfer of plasmids.

Ecologically, many Pseudomonas species in the soil are extremely important as saprophytes. Some species also possess the ability to denitrify the soil, in which case nitrate can be used as an electron acceptor instead of oxygen, thus allowing them to grow in anaerobic conditions. Most species, however, are strictly obligate aerobes. Additionally, while it is more common to find Pseudomonas denitrifying the soil, at least one species is capable of nitrogen fixation.

The type species for this genus is P. aeruginosa. Capable of denitrification, aeruginosa lives primarily in the soil, but can also be found as an opportunistic animal pathogen. Like many, members of its genus, aeruginosa produces a fluorescent pigment. It also produces a characteristic non-fluorescent blue pigment which can be used to distinguish it from other species. As a pathogen, P. aeruginosa can be found in animals primarily in wound, burn and urinary tract infections, as well as in the leaves of tobacco plants.

In this experiment our intention was to isolate P. aeruginosa from soil. To do this we planned to collect and plate soil on Pseudomonas Isolation Agar. This agar would inhibit the growth of most microorganisms while allowing for Pseudomonas species to flourish. We then planned to transfer the growing Pseudomonas colonies to TSA plates to better observe any blue pigment that was produced. However, we were not able to find any colonies which produced a blue pigment and thus concluded that we had not isolated P. aeruginosa, but had instead isolated another member of the Pseudomonas genus. We then proceeded with tests to verify that we had indeed isolated a Pseudomonas species.