As we try to define life, we believe that O2, which is so pervasive in the...

As we try to define life, we believe that O₂, which is so pervasive in the environment, is fundamentally necessary to sustain life. Clostridium & Streptococcus are both catalase-negative bacteria, but only Streptococcus grows by fermentation. Why then is Clostridium killed by O₂, whereas Streptococcus is not?

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Expert Solution

Answer - Both clostridium and streptococcus are anaerobes ,but clostridium is strictly an obligate anaerobe while streptococcus is a facultative anaerobe.

EXPLANATION ;

Anaerobic microorganisms unlike aerobic microorganisms;doesn't requires oxygen for growth.
Depending on the oxygen requirement related to growth microbes are classified into ; Obligate Aerobes,Facultative Anaerobes.Obligate anaerobes,Aerotolerant Anaerobes and micro - aerophiles.
Anaerobes generates the needed energy for them through fermentation and lack the ability to utilize oxygen as the terminal hydrogen acceptor.
Obligate Anaerobes - They lack enzymes like superoxide dismutase and / catalase ; hence will be killed by toxic compounds like hydrogen peroxide and superoxides in the presence of oxygen.Hence oxygen is very toxic to these organisms.Eg - clostridia,Bacteriodes etc.
.Oxygen has strong oxidizing ability and acts as terminal electron acceptor in aerobic and facultative anerobic organisms.During respiration,after the stepwise reduction of oxygen ; some highly reactive intermediates called reactive oxygen species are formed (ROS) that are toxic too.These organisms are adaptable against these toxic compounds as they have developed defense mechanism to protect from these compounds .
Above said defense mechanism include certain enzymes that convert the toxic byproducts into less dangerous ones.
The above mentioned enzymes are absent in Obligate anaerobes but present in aerobes as well as facultative anaerobes .
Facultative anaerobes - they can live in the presence and absence of oxygen .They use fermentation for energy derivation if oxygen is absent while use oxygen as the terminal electron acceptor in its presence.They are adaptable in both the conditions.Eg - Streptococcus,Staphylococcus,salmonella etc.

gladiator answered 1 year ago

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