Anaerobic Respiration
# The respiration process, which uses oxygen as its terminal electron acceptor, is called aerobic respiration and while in anaerobic respiration terminal electron acceptor is not oxygen.
# Anaerobic respiration refers to the special type of respiration, which can take place without oxygen.
Anaerobic respiration is the oldest form of cellular respiration that is carried out by single celled organisms, especially in anoxic environments such as riverbeds, lake mud, bio-gas plants etc.
# It is a process of oxidation of molecules in the absence of oxygen, which results in the production of energy in the form of ATP.
This process is relatively less energy yielding than the aerobic respiration process like for example in alcoholic fermentation or the anaerobic respiration two molecules of ATP are produced for each glucose.
# Bacterial anaerobic respiration is one of the most ancient and essential metabolism processes, which have characteristics of both flexibility and high diversity.
Different Types of Anaerobic Respiration:-
Nitrate reduction
Nitrogen is removed from the environment by both nitrification, the oxidative conversion of ammonia to nitrate and denitrification.
Nitrate reduction can be performed with three different purposes-
a) nitrate assimilation b) nitrate respiration c) nitrate dissimilation
Assimilatory nitrate reduction or nitrate ammonification occurs in Enterobacteriaceae members like E.coli and Enterobacter aerogenes.
This process involves two enzymes nitrate reductase and nitrite reductase. Ammonia is released out at the end of this process.
Denitrification:-
# It is the only biological process that converts oxidized nitrogen back to molecular, hence this process is very significant for nitrogen cycling.
# True The enzymes of denitrification are formed only under anaerobic or low oxygen tension conditions and in most cases nitrate is required as inducer.
# Denitrification is carried out by 4 metalloenzymes that catalyze the steps necessary to reduce nitrate to dinitrogen and are oxygen sensitive.
# These include Nitrate reductase - Nitrate is reduced to nitrite.
Nitrite reductase - Nitrite is reduced to nitric oxide
Nitric oxide reductase - Nitric oxide is reduced to nitrous oxide.
Nitrous oxide reductase - Nitrous oxide is reduced to nitrogen.
# This process is carefully regulated by the microbes since some of the products of the reduction of nitrate to nitrogen gas are toxic metabolism.
# Denitrifying bacteria are capable of utilizing other electron acceptors like nitrite and nitrous oxide in addition to nitrate.
# Nitrate respiration hes been extensively studied in bacteria due to its significance in the global nitrogen cycle.
# Denitrification removes nitrate, an accessible nitrogen source for plants, from the soil and convert it to nitrogen. This decreases soil fertility making farming more expensive.
# The use of high nitrate fertilizers in modern agriculture leads to accumulation of nitrates in soil that makes matters worse as it lead to nitrate pollution, and this is rectified using Denitrification, this process is very significant.
Sulfate Reduction
# In this process in organic sulfur compounds serve as electron acceptors. Sulfate or elemental sulfur are reduced to sulfide, typically in the form of hydrogensulfide. Eight electrons are added to sulfate to form sulfide.Sulfate reduction is similar to oxygen respiration in transfer of electrons and gain of energy of phosphorylation it is called sulfate respiration.
# Eubacteria members which undergo this process are Desulfovibrio, Desulfobacterium, Desulfococcus, Desulfomonas,.etc
# Substrates for sulfate reducers range from Hydrogen gas to aromatic compounds such as benzoate. The most utilized sustrates are acetate, lactate.
# This process takes place both by assimilation and dissimilation pathways.
i) Assimilation pathway is common occurence in almost all bacteria, fungi and plants. these forms produce sulfide necessary for synthesis of sulfur containing amino acids like methionine, cysteine etc
ii) Dissimilatory sulfate reduction is carried out by obligatory anaerobes and takes place through three main enzymes.
ATP sulfurylase - convert sulfate into Adenosine
phosphosulfate(APS ).
APS reductase - converts APS into sulfite
Sulfite reductase - reduces sulfite to sulfide.
# The electron transport chain in these organisms contain c-type or b-type cytochromes, menaquinone, ferrodoxins, havodoxins rubredoxin and desulforedoxin.
# In addition to these ETS also has important and specific protein called siroheme, which exhibit sulfite reductase activity and catalyzes the 6 electron transfer reaction.
# Anaerobic respiration refers to the special type of respiration, which can take place without oxygen.
Anaerobic respiration is the oldest form of cellular respiration that is carried out by single celled organisms, especially in anoxic environments such as riverbeds, lake mud, bio-gas plants etc.
# It is a process of oxidation of molecules in the absence of oxygen, which results in the production of energy in the form of ATP.
This process is relatively less energy yielding than the aerobic respiration process like for example in alcoholic fermentation or the anaerobic respiration two molecules of ATP are produced for each glucose.
# Bacterial anaerobic respiration is one of the most ancient and essential metabolism processes, which have characteristics of both flexibility and high diversity.
Different Types of Anaerobic Respiration:-
Nitrate reduction
Nitrogen is removed from the environment by both nitrification, the oxidative conversion of ammonia to nitrate and denitrification.
Nitrate reduction can be performed with three different purposes-
a) nitrate assimilation b) nitrate respiration c) nitrate dissimilation
Assimilatory nitrate reduction or nitrate ammonification occurs in Enterobacteriaceae members like E.coli and Enterobacter aerogenes.
This process involves two enzymes nitrate reductase and nitrite reductase. Ammonia is released out at the end of this process.
Denitrification:-
# It is the only biological process that converts oxidized nitrogen back to molecular, hence this process is very significant for nitrogen cycling.
# True The enzymes of denitrification are formed only under anaerobic or low oxygen tension conditions and in most cases nitrate is required as inducer.
# Denitrification is carried out by 4 metalloenzymes that catalyze the steps necessary to reduce nitrate to dinitrogen and are oxygen sensitive.
# These include Nitrate reductase - Nitrate is reduced to nitrite.
Nitrite reductase - Nitrite is reduced to nitric oxide
Nitric oxide reductase - Nitric oxide is reduced to nitrous oxide.
Nitrous oxide reductase - Nitrous oxide is reduced to nitrogen.
# This process is carefully regulated by the microbes since some of the products of the reduction of nitrate to nitrogen gas are toxic metabolism.
# Denitrifying bacteria are capable of utilizing other electron acceptors like nitrite and nitrous oxide in addition to nitrate.
# Nitrate respiration hes been extensively studied in bacteria due to its significance in the global nitrogen cycle.
# Denitrification removes nitrate, an accessible nitrogen source for plants, from the soil and convert it to nitrogen. This decreases soil fertility making farming more expensive.
# The use of high nitrate fertilizers in modern agriculture leads to accumulation of nitrates in soil that makes matters worse as it lead to nitrate pollution, and this is rectified using Denitrification, this process is very significant.
Sulfate Reduction
# In this process in organic sulfur compounds serve as electron acceptors. Sulfate or elemental sulfur are reduced to sulfide, typically in the form of hydrogensulfide. Eight electrons are added to sulfate to form sulfide.Sulfate reduction is similar to oxygen respiration in transfer of electrons and gain of energy of phosphorylation it is called sulfate respiration.
# Eubacteria members which undergo this process are Desulfovibrio, Desulfobacterium, Desulfococcus, Desulfomonas,.etc
# Substrates for sulfate reducers range from Hydrogen gas to aromatic compounds such as benzoate. The most utilized sustrates are acetate, lactate.
# This process takes place both by assimilation and dissimilation pathways.
i) Assimilation pathway is common occurence in almost all bacteria, fungi and plants. these forms produce sulfide necessary for synthesis of sulfur containing amino acids like methionine, cysteine etc
ii) Dissimilatory sulfate reduction is carried out by obligatory anaerobes and takes place through three main enzymes.
ATP sulfurylase - convert sulfate into Adenosine
phosphosulfate(APS ).
APS reductase - converts APS into sulfite
Sulfite reductase - reduces sulfite to sulfide.
# The electron transport chain in these organisms contain c-type or b-type cytochromes, menaquinone, ferrodoxins, havodoxins rubredoxin and desulforedoxin.
# In addition to these ETS also has important and specific protein called siroheme, which exhibit sulfite reductase activity and catalyzes the 6 electron transfer reaction.
