<< Chapter < Page Chapter >> Page >

Learning objectives

  • Describe the unique features of deeply branching bacteria
  • Give examples of significant deeply branching bacteria

On a phylogenetic tree (see A Systematic Approach ), the trunk or root of the tree represents a common ancient evolutionary ancestor, often called the last universal common ancestor (LUCA) , and the branches are its evolutionary descendants. Scientists consider the deeply branching bacteria , such as the genus Acetothermus , to be the first of these non-LUCA forms of life produced by evolution some 3.5 billion years ago. When placed on the phylogenetic tree, they stem from the common root of life, deep and close to the LUCA root—hence the name “deeply branching” ( [link] ).

A diagram of a phylogenetic tree. At the base is the label LUCA This branches into two branches. The branch on the left is the bacteria, the branch to the right branches again to form the archaea and Eukarya. The lowest branch of the bacteria is the acetothermus (which is starred). Branches above that include (from bottom to top): aquifex, thermotoga, green filamentous bacteria, bacteroides, cytophaga, planctomyces, gram positives, cyanobacteria, porteiobacteria and spirochetes. Branches of the arcaea from bottom to top: pyrodicticum, thermoproteus, Thermococcus, methanococcus, methanobacterium, methanosarcina, and halophies. Branches of the Eukarya from bottom to top: diplomonads, microsporidia, trichomonads, flagellates, entamoebae, slime molds, ciliates, plants, animals, and fungi.
The star on this phylogenetic tree of life shows the position of the deeply branching bacteria Acetothermus . (credit: modification of work by Eric Gaba)

The deeply branching bacteria may provide clues regarding the structure and function of ancient and now extinct forms of life. We can hypothesize that ancient bacteria, like the deeply branching bacteria that still exist, were thermophiles or hyperthermophiles , meaning that they thrived at very high temperatures. Acetothermus paucivorans , a gram-negative anaerobic bacterium discovered in 1988 in sewage sludge, is a thermophile growing at an optimal temperature of 58 °C. G. Dietrich et al. “ Acetothermus paucivorans , gen. nov., sp. Nov., a Strictly Anaerobic, Thermophilic Bacterium From Sewage Sludge, Fermenting Hexoses to Acetate, CO 2 , and H 2 .” Systematic and Applied Microbiology 10 no. 2 (1988):174–179. Scientists have determined it to be the deepest branching bacterium, or the closest evolutionary relative of the LUCA ( [link] ).

The class Aquificae includes deeply branching bacteria that are adapted to the harshest conditions on our planet, resembling the conditions thought to dominate the earth when life first appeared. Bacteria from the genus Aquifex are hyperthermophiles, living in hot springs at a temperature higher than 90 °C. The species A. pyrophilus thrives near underwater volcanoes and thermal ocean vents, where the temperature of water (under high pressure) can reach 138 °C. Aquifex bacteria use inorganic substances as nutrients. For example, A. pyrophilus can reduce oxygen, and it is able to reduce nitrogen in anaerobic conditions. They also show a remarkable resistance to ultraviolet light and ionizing radiation. Taken together, these observations support the hypothesis that the ancient ancestors of deeply branching bacteria began evolving more than 3 billion years ago, when the earth was hot and lacked an atmosphere, exposing the bacteria to nonionizing and ionizing radiation.

The class Thermotogae is represented mostly by hyperthermophilic, as well as some mesophilic (preferring moderate temperatures), anaerobic gram-negative bacteria whose cells are wrapped in a peculiar sheath-like outer membrane called a toga . The thin layer of peptidoglycan in their cell wall has an unusual structure; it contains diaminopimelic acid and D-lysine. These bacteria are able to use a variety of organic substrates and produce molecular hydrogen, which can be used in industry. The class contains several genera, of which the best known is the genus Thermotoga . One species of this genus, T. maritima , lives near the thermal ocean vents and thrives in temperatures of 90 °C; another species, T. subterranea , lives in underground oil reservoirs.

Finally, the deeply branching bacterium Deinococcus radiodurans belongs to a genus whose name is derived from a Greek word meaning terrible berry . Nicknamed “ Conan the Bacterium ,” D. radiodurans is considered a polyextremophile because of its ability to survive under the many different kinds of extreme conditions—extreme heat, drought, vacuum, acidity, and radiation. It owes its name to its ability to withstand doses of ionizing radiation that kill all other known bacteria; this special ability is attributed to some unique mechanisms of DNA repair.

A micrograph of four round cells forming a square.
Deinococcus radiodurans , or “Conan the Bacterium,” survives in the harshest conditions on earth.

Key concepts and summary

  • Deeply branching bacteria are phylogenetically the most ancient forms of life, being the closest to the last universal common ancestor.
  • Deeply branching bacteria include many species that thrive in extreme environments that are thought to resemble conditions on earth billions of years ago
  • Deeply branching bacteria are important for our understanding of evolution; some of them are used in industry

Fill in the blank

The length of the branches of the evolutionary tree characterizes the evolutionary ________ between organisms.

distance

Got questions? Get instant answers now!

The deeply branching bacteria are thought to be the form of life closest to the last universal ________ ________.

common ancestor

Got questions? Get instant answers now!

Many of the deeply branching bacteria are aquatic and hyperthermophilic, found near underwater volcanoes and thermal ocean ________.

vents

Got questions? Get instant answers now!

The deeply branching bacterium Deinococcus radiodurans is able to survive exposure to high doses of ________.

ionizing radiation

Got questions? Get instant answers now!

Short answer

Briefly describe the significance of deeply branching bacteria for basic science and for industry.

Got questions? Get instant answers now!

What is thought to account for the unique radiation resistance of D. radiodurans ?

Got questions? Get instant answers now!

Questions & Answers

I'm interested in biological psychology and cognitive psychology
Tanya Reply
what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
Amanyire Reply
why is communication effective
Dakolo Reply
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
Wekolamo Reply
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Manix Reply
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
Amesalu Reply
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
Zyryn Reply
good👍
Jonathan
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
Kelu Reply
interpersonal relationships
Abdulfatai Reply
What would be the best educational aid(s) for gifted kids/savants?
Heidi Reply
treat them normal, if they want help then give them. that will make everyone happy
Saurabh
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice MCQ 2

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?

Ask