Proteobacteria is a large and diverse group of bacteria that are classified as Gram-negative. They are known for their varied shapes and metabolic capabilities, which allow them to thrive in many environments, including soil, water, and even inside the bodies of animals and plants. This group includes important bacteria such as Escherichia coli, which is commonly found in the intestines of humans and animals. Many Proteobacteria play crucial roles in ecosystems, such as nitrogen fixation, which helps convert atmospheric nitrogen into a form usable by plants. Some members of this group are also significant in medicine, as they include pathogens responsible for diseases like Salmonella infections and Vibrio cholerae, the cause of cholera.