The phylum Pseudomonadota, formerly known as Proteobacteria, is a major and highly diverse group of bacteria that includes many well-known species important in medicine, ecology, and industry. This phylum encompasses several classes, such as the Alphaproteobacteria (which include Rhizobium, nitrogen-fixing bacteria associated with plants), Betaproteobacteria (such as Neisseria, the cause of meningitis and gonorrhea), Gammaproteobacteria (including Escherichia coli, Salmonella, Vibrio cholerae, and Pseudomonas species), Deltaproteobacteria (known for predatory bacteria like Bdellovibrio and sulfur-reducing bacteria), and Epsilonproteobacteria (such as Helicobacter pylori, linked to stomach ulcers). Members of Pseudomonadota are found in nearly every environment on Earth, ranging from soil and water to the human body, and include both beneficial symbionts and notorious pathogens, making them one of the most ecologically and medically significant bacterial groups.