Pseudomonas is a genus of motile, polar flagellate, non-sporeforming, strictly aerobic bacteria containing straight or curved, but not helical, Gram-negative rods, which occur singly. The metabolism is respiratory, never fermentative. They occur commonly in soil and in fresh water and marine environments. Some species are plant pathogens. One species is a specialized mammalian parasite, while others are only occasionally pathogenic to animals.