Nicknamed "Conan the Bacterium," *Deinococcus radiodurans* is a deeply branching bacterium belonging to a genus whose name is derived from a Greek word meaning "terrible berry." Classified as a polyextremophile, it can survive diverse extreme environments including heat, drought, vacuum, acidity, and radiation. Its unique ability to withstand high doses of ionizing radiation that kill other bacteria is attributed to specialized DNA repair mechanisms.

*Deinococcus radiodurans*

The genus *Acetothermus* is a deeply branching bacterium that represents one of the earliest non-LUCA (last universal common ancestor) lineages of life on Earth, arising approximately 3.5 billion years ago.

*Acetothermus*

Thermotogae is a class of anaerobic, gram-negative bacteria that are primarily hyperthermophilic, though some are mesophilic. A defining characteristic of these bacteria is that their cells are enclosed in a unique, toga-like outer sheath membrane. Additionally, their cell walls contain a thin layer of peptidoglycan with an atypical composition that includes diaminopimelic acid and D-lysine.

Thermotogae

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.

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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

https://openstax.org/details/books/microbiology/

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.

OpenStax Microbiology Textbook

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 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

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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