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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

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

common ancestor

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

vents

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

ionizing radiation

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Short answer

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

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

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Questions & Answers

reactions if viruses to physical and chemical agents?
VICTOR Reply
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
Asali
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
bacteria
ABUBAKAR
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
Asali
yes
Dhirender
not 'things'...'organisms' like bacterias, viruses and fungi
Sinmi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
Richard
bacterium is obvio in a singular form but plural of bacterium is bacterias
Sinmi
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
Aakriti
what is microbiology?
Sandeep Reply
what is microbiology
Glory
is the study of small microorganisms that can't be viewed by our naked eyes under a microscope
Nabukwasi
it's the study of microbes their classification, diversity, their cellular structure and processes, their applications and interaction with other organisms.
Chaitanya
what is EMP pathway
rajesh
which organism is implicated in meningoencephalitis
Peter Reply
Herpes virus
Carlos
Yeah
Laxmi
which mold is called dairy mold?
Gopinath
mushroomm
Top
Geotrichum candidum
Gopinath
hi
bio
Hlw
Laxmi
which infectious agent is the smallest
Sinmi
spore or virus
Anushree
prion ....it is a single protein in a misfolded form..there is also a theory based on it
Sinmi
yup...m sry
Anushree
yes it can be turned as a virus
Sinmi
which gram positive bacteria is responsible for food poisoning?
Sinmi
prion is not a living organism yet it is infectoois why
Jeevan
prions are virus like organism. and it is a misfolded protein that may cause disease to us.
Tharra
Clostridium perfringens, B.cereus
Sneha
Who is the father of the biology
Dhirender
I have one more question. . that who is the father of botany and medicine? ? can any one tell
Dhirender
define polar bond in simple way
Rashmi Reply
when there is formation of positive and negative poles i.e. one atom is +ve and other is -ve which further results in the dipole moment. Such bond is know as polar bond. It is a convalent bond only.
Aakriti
Hi everyone, is these site only about microbiology? I want a site which I can download articles on hematological and biochemical profile
Peter Reply
I think it is only about micro biology.
Kimberly
so whats happening
Michael
I am about to enter school and am going for MCB
Olugbenga Reply
What is DNA damage and repair
Sree Reply
removal of nucleotide bases from DNA is damage n addition or insertion of bases in DNA is repair.
Rashmi
replication is a term related to generation of new DNA from a parental DNA.
Rashmi
role of microorganism as pathogens
Parteek Reply
to live inside the host body, reproduction n destroy the immune system of host body.
Rashmi
what is replication
rajesh
please give me ans
rajesh
replication is a term related to generation of new DNA from parental DNA.
Rashmi
difference between endotoxin and exotoxin
Binkheir Reply
toxins released inside the cell or a body is endotoxin n toxins released outside the cell or a body is exotoxin.
Rashmi
Generally, exotoxins are produced by gram positive bacteria and endotoxins are the integral part of the cell wall of gram negative bacteria. But some gram negative bacteria can also produced exotoxins such as E.coli.
Aakriti
Yeah u r ryt aakarti exotoxins screted by gram postive bacteria nd secreted by cell surface and they are secondary metabolites ....On the other hand endotoxin released by gram negtive bacteria nd released inside the cell (lipopolysaccharide) ..
Bharat
Heat stable lipopolysaccharides to be exact.
Aakriti
yup..
Bharat
please I want the names of bacteria and the diseases they cause.
Ibrahim Reply
there are many we classify it according to their shapes gram negative or gram positive
Tharra
so u may refer the book u guess or by when u want I can do a list for you and send u here
Tharra
😊
Tharra
please do a list for me
Ibrahim
I have the lost but it's too much to type ..
Tharra
MSc entrance prepare books and questions LA etha base pani irukum..
Guhan Reply
kushal always prescott is the imp book to follow.search some objective mcqs books based on your syllabus
deepthi Reply
I want to clear entrance of ms university so I have no more idea so my preparation is based on my bachlor studies.
Kushal
what are the opportunistic infection in aids stage
Kalkak
certain cancer or pneumonia 🤔
Kushal
penicillium crysogenum
Kushal Reply
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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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