Pseudomonas belongs to the rRNA group I organism of gamma proteobacteria. They are Gram-negative aerobic rod-shaped with polar flagella. They can be isolated from soil, rotting plant matter, and the rhizospheric region of many plant species. Strains of these bacteria called P. marginalis or P. fluorescens can be attributed to soft rot of vegetables. The highly complex groups of fluorescent, oxidase-positive soft rot Pseudomonas are opportunistic macergens. The nomenclature of bacteria in the genus Pseudomonas has changed considerably in recent decades. P. marginalis are pectinolytic strains of P. fluorescens that cause soft rot on a wide range of hosts. The taxonomic and phytopathogenic status of P. marginalis is not well known, but it is biochemically and phenotypically indistinguishable from saprophytic strains of P. fluorescens biovars II, P. putida, and P. chlororaphis (now includes P. aureofaciens). Due to their ability to degrade pectin and macerate the parenhymatous tissues of the plant, they are called P. marginalis. Recently, based on 16S rRNA analysis, Anzai et al. (2000) proposed 57 strains of Pseudomonas sensu stricto with seven subgroups: the P. syringae group, the P. chlororaphis group, the P. fluorescens group, the P. putida group, the P. stutzeri group, the P. . aeruginosa and the P. pertucinogena group. . Additionally, within the same genus Pseudomonas, some species have been misclassified, for example P. aureofaciens and P. aurantiaca, which were reclassified as P. chlororaphis (Peix et al. 2007). Since the invention of the genus Pseudomonas, many taxonomic changes have taken place, not only with regard to the number of species included, but also with regard to the criteria used for their definition and delimitation. In Berg...... middle of paper ......ies (Guasp et al. 2000). The selection of the minimum principles necessary for the delimitation and description of species is selected for each bacterial genus by a committee created by experts in the given genus. The methods used in the taxonomy of the genus Pseudomonas and its related genera have been standardized by the Subcommittee on Taxonomy. However, minimum standards for the description of species in the genus Pseudomonas have yet to be defined after the 2002 meeting of this subcommittee (De Vos and Yabuuchi 2002). Therefore, the new description of species in this genus should be based on the general minimum standards for the characterization of bacterial species (Stackebrandt et al. 2002). These general minimum standards necessary for the classification of new species and/or subspecies must include 16S rRNA sequencing, DNA-DNA hybridization, fatty acid analysis and phenotypic classification..