Deeply branching bacteria occupy early-diverging positions on the tree of life and offer clues about conditions faced by ancient organisms. This lesson explores how scientists interpret their evolutionary position and examines notable groups and species adapted to extreme environments.
A phylogenetic tree represents evolutionary relationships. Its root represents a common ancient ancestor, often called the last universal common ancestor (LUCA), while branches represent descendant lineages. Deeply branching bacteria appear on branches that emerge close to this root. “Deeply branching” describes their position on the tree; it does not mean that these bacteria are unchanged ancestors or that modern species are LUCA itself.
All flashcards
What is LUCA?
LUCA is the last universal common ancestor, the common ancient ancestor represented at the root of the phylogenetic tree.
What does “deeply branching” mean?
It describes a lineage that diverges early on a phylogenetic tree, close to its root. It does not mean a modern species is unchanged or is LUCA.
What are key traits of *Acetothermus paucivorans*?
It is a gram-negative, anaerobic thermophile with an optimal growth temperature of about 58 °C. It was discovered in sewage sludge and is described as a deeply branching bacterium.
What is distinctive about Thermotogae?
Their cells have a sheath-like outer membrane called a toga. They use organic substrates and produce molecular hydrogen; some are hyperthermophiles and others are mesophilic.
How does *Deinococcus radiodurans* withstand intense radiation?
Distinctive DNA-repair mechanisms help it withstand ionizing radiation. It also survives other extreme conditions, making it a polyextremophile.
Quiz questions
What does the root of a phylogenetic tree represent?Answer: The common ancestral lineage from which the represented lineages descend.
What does “deeply branching” describe in evolutionary biology?Answer: An early-diverging lineage positioned close to the tree’s root.
What structure gives Thermotogae their distinctive name?Answer: A sheath-like outer membrane called a toga.
Why is *Deinococcus radiodurans* described as a polyextremophile?Answer: It can survive several extreme conditions, including radiation, heat, and drought.
Which group includes hyperthermophiles that can use inorganic substances as nutrients?Answer: Aquificae
Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.