The methanogens are strict anaerobic archaea that produce methane during
anaerobic respiration. Methanogens are found in deeper regions of oil reservoirs,
utilizing the acetate, one carbon compounds, and H 2 and CO 2 (Prajapat et al. 2019).
Generally, methanogens are present with syntrophs (an obligate proton producing
bacteria).
6.2.1 Sulfate Reducing Bacteria
Sulfate reducing bacteria (SRB) are morphologically diverse and anaerobic
organisms obtaining energy by dissimilatory reduction of sulfate to sulfide
(Bernardez and De Andrade Lima 2015). The SRB and sulfate reducing archaea
(SRA) are together known as sulfate reducing prokaryotes (SRP). During the sulfate
reduction process, these SRP communities oxidize the organic compounds (oil
components in the oil reservoir) and reduce sulfate into hydrogen sulfide (H 2 S).
SRP are also found to have the ability to utilize other sulfur compounds such as
sulfite, dithionite, thiosulfate, trithionate, elemental sulfur, and polysulfides.
The sulfate reduction processes are of two types, assimilatory sulfate reduction
and dissimilatory sulfate reduction. During assimilatory sulfate reduction, the final
product of sulfate reduction is used for the biosynthesis of sulfur containing
biomolecules, while dissimilatory sulfate reduction produces H 2 S which is released
in the surrounding environments. Dissimilatory sulfate reduction is a three step
process: In the initial step, sulfate is reduced into adenosine-5
0 -phosphosulfate
(APS) with the help of the ATP sulfurylase enzyme. Then, APS is converted into
sulfite and adenosine monophosphate (AMP) with the help of APS reductase
enzyme. During the last step, produced sulfite is further converted into H 2 S with
the help of dissimilatory bisulfite reductase (Dsr) enzyme (Prajapat et al. 2019).
SRP communities are known to be phylogenetically distributed variably along the
oil fields. Such as, the presence of SRB depends upon the oil field origin, oil
composition, downhole temperature, pH of oil–water mixture, depth of the reservoir,
stage of oil production, and salinity of produced water. The variance of SRP
communities also differs worldwide in different oil fields. The general SRB
communities present in varies oil field setup are Desulfotomaculum,
Desulfosporosinus,
Thermodesulfobacterium,
Thermodesulfovibrio,
Thermodesulfobium,
Thermotoga,
Thermodesulfohabdus,
Desulfacinium,
Desulfobulbus, Desulfocapsa, Desulfofustis, Desulforhapalus, Desulfobotulus,
Desulfotignum, Desulfobacter, Desulfobulbus, and Desulfovibrio (Prajapat et al.
2019). While SRA present in various oil fields are Archaeoglobus fulgidus,
Archaeoglobus profundus, Archaeoglobus veneficus, and Caldivirga maquilingensis
(Prajapat et al. 2019).
Moreover, beside there divergence the SRP population are widely distributed
among the oil field facilities. These microbes thrive in-between the oil and water
phases. They mostly inhabit in the injection, production, and crude oil processing
facilities. As these SRP population grow in different environments, they showed
varied types of physiology. The SRP present in the oilfields are mesophilic,
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G. Prajapat et al.
anaerobic respiration. Methanogens are found in deeper regions of oil reservoirs,
utilizing the acetate, one carbon compounds, and H 2 and CO 2 (Prajapat et al. 2019).
Generally, methanogens are present with syntrophs (an obligate proton producing
bacteria).
6.2.1 Sulfate Reducing Bacteria
Sulfate reducing bacteria (SRB) are morphologically diverse and anaerobic
organisms obtaining energy by dissimilatory reduction of sulfate to sulfide
(Bernardez and De Andrade Lima 2015). The SRB and sulfate reducing archaea
(SRA) are together known as sulfate reducing prokaryotes (SRP). During the sulfate
reduction process, these SRP communities oxidize the organic compounds (oil
components in the oil reservoir) and reduce sulfate into hydrogen sulfide (H 2 S).
SRP are also found to have the ability to utilize other sulfur compounds such as
sulfite, dithionite, thiosulfate, trithionate, elemental sulfur, and polysulfides.
The sulfate reduction processes are of two types, assimilatory sulfate reduction
and dissimilatory sulfate reduction. During assimilatory sulfate reduction, the final
product of sulfate reduction is used for the biosynthesis of sulfur containing
biomolecules, while dissimilatory sulfate reduction produces H 2 S which is released
in the surrounding environments. Dissimilatory sulfate reduction is a three step
process: In the initial step, sulfate is reduced into adenosine-5
0 -phosphosulfate
(APS) with the help of the ATP sulfurylase enzyme. Then, APS is converted into
sulfite and adenosine monophosphate (AMP) with the help of APS reductase
enzyme. During the last step, produced sulfite is further converted into H 2 S with
the help of dissimilatory bisulfite reductase (Dsr) enzyme (Prajapat et al. 2019).
SRP communities are known to be phylogenetically distributed variably along the
oil fields. Such as, the presence of SRB depends upon the oil field origin, oil
composition, downhole temperature, pH of oil–water mixture, depth of the reservoir,
stage of oil production, and salinity of produced water. The variance of SRP
communities also differs worldwide in different oil fields. The general SRB
communities present in varies oil field setup are Desulfotomaculum,
Desulfosporosinus,
Thermodesulfobacterium,
Thermodesulfovibrio,
Thermodesulfobium,
Thermotoga,
Thermodesulfohabdus,
Desulfacinium,
Desulfobulbus, Desulfocapsa, Desulfofustis, Desulforhapalus, Desulfobotulus,
Desulfotignum, Desulfobacter, Desulfobulbus, and Desulfovibrio (Prajapat et al.
2019). While SRA present in various oil fields are Archaeoglobus fulgidus,
Archaeoglobus profundus, Archaeoglobus veneficus, and Caldivirga maquilingensis
(Prajapat et al. 2019).
Moreover, beside there divergence the SRP population are widely distributed
among the oil field facilities. These microbes thrive in-between the oil and water
phases. They mostly inhabit in the injection, production, and crude oil processing
facilities. As these SRP population grow in different environments, they showed
varied types of physiology. The SRP present in the oilfields are mesophilic,
116
G. Prajapat et al.