Phototrophic purple and green bacteria are classified based on their utilization of sulfur compounds for oxidation. Sulfur bacteria perform anoxygenic photosynthesis using sulfur compounds as electron donors, while nonsulfur bacteria use organic compounds, such as succinate and malate, as electron donors.

Classification of Purple and Green Bacteria

Purple and green bacteria are a group of phototrophic bacteria that carry out photosynthesis using bacteriochlorophylls, which are green, purple, or blue pigments similar to plant chlorophyll. Some of these bacteria also contain carotenoids—red or orange pigments—enabling them to absorb light at different wavelengths and display colors ranging from orange and red to purple and green.

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Phototrophic bacteria represent a diverse category of bacteria, rather than a single taxonomic group, characterized by their ability to use sunlight as an energy source. They include both Proteobacteria and nonproteobacteria, as well as purple or green sulfur and nonsulfur bacteria, with some species being capable of nitrogen fixation.

Phototrophic Bacteria

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

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Cyanobacteria are a phylum of blue-green phototrophic bacteria that contain chlorophyll and perform oxygenic photosynthesis. They are hypothesized to have played a critical role in oxygenating Earth's anoxic atmosphere approximately $${}1$$–$${}2$$ billion years ago.

Cyanobacteria

Purple and Green Bacteria 

Phototrophic bacteria perform either oxygenic photosynthesis, which produces oxygen, or anoxygenic photosynthesis, which does not generate oxygen. Except for certain cyanobacteria, most phototrophic bacteria engage in anoxygenic photosynthesis.

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