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 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.

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.

Photosynthetic Pathways in Phototrophic Bacteria

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.

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Modern bacterial taxonomy classifies bacteria using physiological, biochemical, and genetic traits. This classification includes a unique category of deeply branching bacteria, which represent the oldest evolutionary lineages. Additionally, gram-negative bacteria are further divided into Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB), and spirochetes, while gram-positive and other bacterial groups continue to be categorized based on their distinct physiological and genomic properties.

Bacterial Diversity

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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.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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Deeply branching bacteria are the phylogenetically oldest forms of life and the closest relatives to the last universal common ancestor. They often live in extreme environments that mimic the conditions of ancient Earth billions of years ago, making them crucial for studying evolutionary history and useful for industrial processes.

Deeply Branching Bacteria

Non-proteobacteria gram-negative bacteria are a group of gram-negative bacteria that do not belong to the Proteobacteria phylum. This group includes spirochetes, the Cytophaga-Flavobacterium-Bacteroides (CFB) group, Planctomycetes, and Chlamydia species.

Non-proteobacteria Gram Negative Bacteria

Proteobacteria is a major phylum of gram-negative bacteria whose establishment as a separate phylum within the domain Bacteria was proposed in 1987 by American microbiologist Carl Woese, based on the similarity of their genomic nucleotide sequences. Originally termed 'purple bacteria and their relatives' by Woese, this diverse phylum contains both normal human microbiota and pathogens, and is divided into five classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria.

Proteobacteria

Phototrophic Bacteria

Gram-positive bacteria represent a large and diverse group of microorganisms whose taxonomy and unique traits are critical for diagnosing and treating infectious diseases. These bacteria are categorized into high G+C and low G+C gram-positive groups, depending on the abundance of guanine and cytosine nucleotides within their genomes.

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