<< Chapter < Page Chapter >> Page >

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 pathogenic
kelvin Reply
biological pathogen is anything that can produce disease. a pathogen may also be referred to as an infectious agent, or simple a germ.
explain 3 points why gender is relevant to health.
wat causes sor throat
Ezeama Reply
Gram positive
streptococcus pyrogenes
group A streptococcus pyogenes. But not the only one.
does the bac of s.aures gives choronic diseas in bone?
causes virus bac group A strep allergies smoking
truth also virus
what z microbiology
Mwelwa Reply
microbiology is all about the scientific study of microorganisms, their life changes, their life span, structural punctuality and their phenomenon.
Best scope in microbiology
wat abut skin
whatis scope
what is scope
what happened when someone died and what happened to the blood
Franca Reply
nice question
when you die you have no memory and the blood dry off
what microorganisms is all about?
And how many does the microorganisms is classified?
How are microbs organized
what is endoparasites and exo parasite and their example
Endo : inside the body Exo/ecto : outside or on the body
examples please
Louse for exo/ecto Helminths (worms) for endo
what's prokaryotic
mohaiminul Reply
A prokaryotic cell is a cell with no membrane bounds organelles
what are the main effect of parasite?
yunusa Reply
nutritional group of micro organism
Mana Reply
what are the charateristic bacteria, eukaryotes, and viruses have in commom
Ami Reply
what type of bacteria ismor serious
D N A ar purno rup ki
Ruba Reply
বাংলায় দেখবো DNA এর পূর্রন্যরুপ কি
what's microbiology
micro biology is the study of micro organisms,those being unicellular multicellular or a cellular
deoxyribonucleic acid is a long molecule that contains our unique genetic code.
Does the parasite/parasitology are under microbiology or not
Define bacteria
Bacteria are a type of biological cell & they constitute a large domain of prokaryotic microorganisms.
what kind of microbiology
hello what is main function of T and B cells
Ishaq Reply
T cells are involved in cell-mediated immunity while B cells are primarily responsible for humoral immunity (relating to antibodies)
what is hepatitis B
it's viral infection that attacks the liver and can cause both acute and chronic diseases. the virus is most commonly transmitted from mother to child during birth and delivery, as well as through contact with blood or other body fluids...
What are fundamental experiment of microbiology?
Lucky Reply
study of microscopic organisms, unicellular and multicellular
what are the characteristics of bacteria, viruses, and eukaryotes
bacteria-are living organism. contain a peptidoglycan/lipopolysaccharide cell wall. VIRUS-are considered as organic structure which interact with living organism don't have acell wall. they have many differents like bacteria size -large(1000nm) virus size-smaller(20-400nm). bacteria ribosomes presen
virus ribosomes absence. bacteria living organism. virus b/n living and non-living things
eukaryotic cell has a true membrane bond nucleus and has other membranous organelles that allow for compartmenalization of function
This answer is wrong
Jeffrey Reply
who discovered the growth curve
Joy Reply
Example of coccus bacteria
Nweke Reply
staphylococcus aureus
MRSA any bew information
pl. read any new information about MRSA
Any stru tural finding about novel corona virus

Get the best Microbiology course in your pocket!

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?