Pseudomonas stutzeri is a Gram-negative soil bacterium that is motile, has a single polar flagellum, and is classified as bacillus, or rod-shaped.[1][2] While this bacterium was first isolated from human spinal fluid, [3] it has since been found in many different environments due to its various characteristics and metabolic capabilities.[4] P. stutzeri is an opportunistic pathogen in clinical settings, although infections are rare.[3] Based on 16S rRNA analysis, this bacterium has been placed in the P. stutzeri group, to which it lends its name.[5] Taxonomy P. stutzeri is most easily differentiated from the other Pseudomonas spp. in that it does not produce fluorescent pigments.[6] P. mendocina, P. alcaligenes, P. pseudoalcaligenes, and P. balearica are classified within the same branch of pseudomonads as P. stutzeri based on 16S rRNA sequences and other phylogenetic markers.[6] Of this group, P. stutzeri is most closely related to P. balearica and they can be differentiated not only by the 16S rRNA sequences, but also by the ability of P. stutzeri to grow above 42 °C.[7] P. stutzeri has been isolated in many different locations, and since each strain is a little different based on where it was isolated, the P. stutzeri group contains many genomovars.[6] This means that the many strains of P. stutzeri can be considered genospecies, which are organisms that can only be differentiated based on their nucleic acid composition