Alphaproteobacteria is a class of bacteria within the phylum Proteobacteria. These microorganisms are diverse and can be found in various environments, including soil, water, and as symbionts in plants and animals. Some members are known for their ability to perform photosynthesis, while others are important in nitrogen fixation. Many Alphaproteobacteria are also significant in human health and agriculture. For example, Rhizobium species form beneficial relationships with legumes, aiding in nitrogen uptake. Additionally, some Alphaproteobacteria are pathogens, such as Rickettsia, which can cause diseases in humans.