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Learning objectives

  • Interpret visual data demonstrating minimum, optimum, and maximum oxygen or carbon dioxide requirements for growth
  • Identify and describe different categories of microbes with requirements for growth with or without oxygen: obligate aerobe, obligate anaerobe, facultative anaerobe, aerotolerant anaerobe, microaerophile, and capnophile
  • Give examples of microorganisms for each category of growth requirements

Ask most people “What are the major requirements for life?” and the answers are likely to include water and oxygen. Few would argue about the need for water, but what about oxygen? Can there be life without oxygen?

The answer is that molecular oxygen (O 2 ) is not always needed. The earliest signs of life are dated to a period when conditions on earth were highly reducing and free oxygen gas was essentially nonexistent. Only after cyanobacteria started releasing oxygen as a byproduct of photosynthesis and the capacity of iron in the oceans for taking up oxygen was exhausted did oxygen levels increase in the atmosphere. This event, often referred to as the Great Oxygenation Event or the Oxygen Revolution , caused a massive extinction. Most organisms could not survive the powerful oxidative properties of reactive oxygen species (ROS), highly unstable ions and molecules derived from partial reduction of oxygen that can damage virtually any macromolecule or structure with which they come in contact. Singlet oxygen (O 2 •), superoxide ( O 2 ) , peroxides (H 2 O 2 ), hydroxyl radical (OH•), and hypochlorite ion (OCl ), the active ingredient of household bleach, are all examples of ROS. The organisms that were able to detoxify reactive oxygen species harnessed the high electronegativity of oxygen to produce free energy for their metabolism and thrived in the new environment.

Oxygen requirements of microorganisms

Many ecosystems are still free of molecular oxygen. Some are found in extreme locations, such as deep in the ocean or in earth’s crust; others are part of our everyday landscape, such as marshes, bogs, and sewers. Within the bodies of humans and other animals, regions with little or no oxygen provide an anaerobic environment for microorganisms. ( [link] ).

a) A photograph of a bog. B) A photograph of cows.
Anaerobic environments are still common on earth. They include environments like (a) a bog where undisturbed dense sediments are virtually devoid of oxygen, and (b) the rumen (the first compartment of a cow’s stomach), which provides an oxygen-free incubator for methanogens and other obligate anaerobic bacteria. (credit a: modification of work by National Park Service; credit b: modification of work by US Department of Agriculture)

We can easily observe different requirements for molecular oxygen by growing bacteria in thioglycolate tube culture s. A test-tube culture starts with autoclaved thioglycolate medium containing a low percentage of agar to allow motile bacteria to move throughout the medium. Thioglycolate has strong reducing properties and autoclaving flushes out most of the oxygen. The tubes are inoculated with the bacterial cultures to be tested and incubated at an appropriate temperature. Over time, oxygen slowly diffuses throughout the thioglycolate tube culture from the top. Bacterial density increases in the area where oxygen concentration is best suited for the growth of that particular organism.

Questions & Answers

what a tropism in host
Khaliil Reply
HPV vaccine given to school children
Jayani Reply
Differentiation between electron, proton and neutron
Zainab Reply
proton .possitive charge electron . negative charge neutron . having no charge
proton positive charge. electron negative charge. And no charge of the neutron.
the nucleus is composed of electrons (-) charge and they turn around the Nucleon the Nucleon = neutron(no charge) + proton (+) a neutron can turn to a proton and vice versa (cuz they have the same mass=1)
what are the roles of microorganisms in human being
Buhari Reply
some causes disease, others are not disease causing
they're necessary in our digestive system+the skin,everywhere actually the number of them in the human body alone is higher(by millions)than the number of humans cells,they're indispensable in the food industry,others are fundamental to make medicines and more,what exactly are you asking about ?
What are the natural occurring elements found in organisms on earth?
Otu Reply
some of the naturally occurring elements found in organisms are carbon, nitrogen, hydrogen, oxygen
some of them are carbon, oxygen, nitrogen, hydrogen, phosphorus and sulfur
what is Zika virus?
Somali Reply
Zika virus is a mosquito-borne flavivirus that was first identified in Uganda in 1947 in monkeys. 
in pregnancy it can cause the unborn child's head to underdevelop so that it does not grow along with the rest of the body
intracellular vesicles are found in
Akshay Reply
how do i report widal slide results
Isaac Reply
how food can be used as a substrate for the growth of microorganisms
Ashi Reply
what is the importance of understanding chemistry in the field of microbiology and food technology?
Charmaine Reply
What is different between eukaryotes and prokcaryotic
Abia Reply
main difference is that eukaryotic cells possess membrane bound organelles
prokaryotes are primitive organisms that doesn't contain membrane bound nucleus or any orgenelle while in eukaryotes membrane bound orgenelles and nucleus is present
what s anatomy
jane Reply
its mean body structure, function, and systems
study of internal structure of living things
anatomy is the study structure of the made human
anotomy is the actual study of body internally and externally Which include how itis made. for what and what is need of this
la science anatomie c'est la science qui nous aide à étudier l'homme
Ancestor are they real
Rapheal Reply
yes of course
yes please
50 50, depending on the accuracy of the clan records.
Why protist is not a kingdom of Linnaeus 'S taxonomy?
Neha Reply
I dont know
Linnaeus used Aristotle's criteria for dividing living organisms into kingdoms. Plants are immobile and insensitive, while animals are mobile and sensitive. the creatures he saw through the microscope were mobile, so he attributed them to animals.
name the different types of media use in lab to detect the micro organisms
Shehzadi Reply
The different types of media used in the lab to detect the microorganisms is known as cell culture..
solid media or broth is used to grow and detect microorganisms
what is microbiology
the study of large living organisms
the study of organisms which are micro in range
what is autoclaving?
process for sterilization
is a machine used on the process of sterilisation
what is difference between hot air oven and autoclave as they both are used for sterilization ?
autoclave basically do moist heat sterilization while hot air oven do sterilization by dry heat.....
what is the microbe
which method out of these two is best?
why human have microbe
hi to all
depends on what to sterilize
what is knowledge
well idea

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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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