Thioglycolate broth is used in test tubes to identify bacteria based on their oxygen requirements. Obligate aerobes gather at the top where oxygen is highest, obligate anaerobes gather at the bottom where oxygen is lowest, and facultative anaerobes gather mostly at the top because aerobic respiration generates more ATP than other methods. Microaerophiles gather in the upper part but not the very top as they are poisoned by oxygen but need it, while aerotolerant bacteria can be found throughout as they do not require oxygen.

1. Thioglycolatemedium
Anaerobic bacteria can be identified by
growing in test tubes of Thioglycolate
broth.
TEST FOR OXYGEN REQUIREMENTS OF MICROORGANISMS

2. Effect of thioglycolate broth on different bacteria .

3. Obligate Aerobes :- needs
oxygen because they cannot
ferment or respire
anaerobically. They gather
at top of the test tube
where oxygen concentration
highest.

4. Obligate anaerobe :- Are
poisioned by oxygen so
they gather at the bottom
of the test tube where
oxygen concentration is
lowest.

5. Facultative anaerobes:- Can grow with
or without oxygen because they
can metabolise energy aerobically
or anaerobically. They gather
mostly at the top because aerobic
respiration generates more ATP
than either fermentation or
anaerobic respiration

6. Microaerophile:- Needs oxygen
because they cannot
ferment or respire
anaerobically. However,
they are poisoned by
oxygen. They gather in
upper part of test tube but
not very top.

7. Aerotolerant:- Do not require
oxygen as they metabolise
energy anaerobically. Unlike
obligate anaerobes, however
they are not poisioned by
oxygen. They can be found
evenly spread throughout the
test tube.

8. Campylobacter, a type of capnophie
A Miacroaerophile is a microorganism that requires oxygen to survive , but requires env’s
Containing lower levels of oxygen than present in atmosphere. (typically 2-10% of oxygen)
Many microaerophiles are capnophiles requiring an elevated concentration of
carbondioxide (ex.- 10% in case of campylobacter species).