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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 is cell
Avi Reply
is unit of life
who is an industrial microbiologist
Cynthia Reply
I want to know the biochemical composition of bacteria
Josh Reply
It contains peptidoglcon, DNA nd RNA
bacteriophage disadvantage
Momina Reply
disease due to __________ abnormalities are termed primary immunodeficiencies
Tayee Reply
Some primary immunodeficiencies are due to a defect of a single cellular or humoral component of the immune system.
Examples of primary immunodeficiencies include: chronic granulomatous disease, X-linked agammaglobulinemia, selective IgA deficiency etc
thank you
explain microbial mutation
what is mutation
Cynthia Reply
alteration in genetic makeup
Hi, I'm new here. I'm Bello Abdul Hakeem from Nigeria.
welcome on board
Thanks brother I'm an undergraduate. I hope to study for MBBS.
pls guys help me out
what is limitation of plate
limitation of plate load test . there are some that should be considered while performing load test which are given below, this test is usually performed on relatively similar plate ,usually 1 or 2 square foot area the reason is that the plate of greater are the economically not feasible
iam new here my name shafiu umar from Nigeria
thanks shafiu
how to differentiate Gram positive from Gram negative bacteria?
by the cell membrane
with gram staining which has 4 steps
Mechanism of bacterial pathogenicity
rashida Reply
write a short note on Algea
najaatu Reply
green minutes plants organisms that are produced in turf.
Algae is a kind of a photosynthetic organism, which is usually grown in the moist areas. These are usually the simple plants that grow near to the water bodies. It contains a kind of chlorophyll pigments that act as a primary coloring agent.
they are eukaryotic and most lived in fresh water. they are photosynthetic that's, they contain chlorophyll and store starch in discrete chloroplast.
are bacteria important to man
just Reply
yes, depending on the type of bacteria .eg the normal florals, the latic acid batteries etc are important to man
I mean latic acid bacterial
I don't understand this topic
Jane Reply
what topic is that
sahi kon hai bhosri ke
saurabh Reply
define metabolism of carbohydrates with example
Thavasi Reply
what is sterilization a
the process of keep equipment free from bacteria
is it only bacteria?
no undesirable fungi and contamination also.
what is streak plate method
what is the biofilm
metabolism is the sum of all the biochemical reaction required for energy generation and use of that energy to synthesize cell materials from small molecules in environment.
what are granulocytes
Shawnitta Reply
granulocytes are type of WBCs which contains granules in the cytoplasm
what is mutation
it is the interchange of genes from their normal sequence
is an heritable change of the base-pair sequence of genetic material
suitable example for prokaryotes
Suvetha Reply
one of the possible early sources of energy was
uv radiation and lighting
e coli is the example of prokaryotes
archaea too

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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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