(II), Ni(II), Cd(II) and Fe(II)]. The most relevant resistance mechanism in bacteria is
related to the P1B-type ATPases and chemiosmotic systems (Naghma et al. 2005;
Silver and Phung 2005). Genomic studies of the interrelationships to metal-induced
proteome and metabolome changes allow in silico searches for genes encoding
metal-responsive proteins (Haferburg and Kothe 2010; Chance et al. 2004). The
proteins encoded could be either involved in metal homeostasis, thus being of
interest for improving metal resistance of strains for bioremediation.
13.4 Sulfate-Reducing Bacteria
Reducing sulfates constitute a group of obligate anaerobic prokaryotes (bacteria and
archaea); they present a morphological and physiological diversity. These
microorganisms live in anoxic habitats and have great ecological importance in the
carbon and sulfur cycles, because they mineralize the organic matter of the anaerobic
environments. In marine sediments, 50% of organic matter is oxidized by sulfate
reduction with an equivalent or higher yield than in an aerobic process (Barton
1995). Within this group of prokaryotes, the sulfate-reducing bacteria (SRB) are the
most abundant and are widespread in natural habitats such as marine sediments,
lakes and saltwater lagoons and oil fields, as well as in the gastrointestinal tracts of
many animals, including humans. In environments with low sulfate levels, such as
bodies of freshwater, they have relevance in the mineralization of organic matter
(Muyzer and Stams 2008). Some SRB are able to survive in the presence of oxygen,
but no growth has been observed (Fournier et al. 2004). Also, SRB have industrial
(biocorrosion), environmental (bioremediation) and health (inflammation of the
intestine) implications (Bartosch et al. 2004); consequently, the SRB have been
studied extensively.
Sulfate-reducing bacteria were discovered by Martinus Willem Beijerinck in
1895 and described as the use of enrichment cultures for “sulfur fermentation”.
With his cultivation technique, he was able to isolate colonies surrounded by a black
precipitate, ferrous sulfide. Beijerinck had isolated the first sulfate-reducing bacteria
from the Dutch city canal in Delft. The morphological description of the bacterium
corresponded to curved bacilli with movement, which is the reason why it was
named Spirillum desulfuricans. Beijerinck also suggested studying other terminal
electrons acceptors, besides sulfate, and studying the distribution of these bacteria in
marine environments and soil (Voordouw 1995). SRB are chemolithotrophic
microorganisms, capable of using sulfate as the final electron acceptor in the
degradation of organic matter, a process called sulfate reduction, where hydrogen
sulfide is generated. The dissimilatory reduction of sulfate is a large-scale process
limited to SRB; however, they can also reduce other oxidized forms of sulfur such as
sulfite and thiosulfate and other inorganic compounds as nitrite or nitrate. Some SRB
are able to integrate elemental sulfur as a substrate in the respiration, and other SRB
can even respire with oxygen. SRB can grow in a sulfate-dependent manner using
hydrogen and a wide range of organic compounds, but polymeric compounds as
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M. I. Neria-González and R. Aguilar-López
related to the P1B-type ATPases and chemiosmotic systems (Naghma et al. 2005;
Silver and Phung 2005). Genomic studies of the interrelationships to metal-induced
proteome and metabolome changes allow in silico searches for genes encoding
metal-responsive proteins (Haferburg and Kothe 2010; Chance et al. 2004). The
proteins encoded could be either involved in metal homeostasis, thus being of
interest for improving metal resistance of strains for bioremediation.
13.4 Sulfate-Reducing Bacteria
Reducing sulfates constitute a group of obligate anaerobic prokaryotes (bacteria and
archaea); they present a morphological and physiological diversity. These
microorganisms live in anoxic habitats and have great ecological importance in the
carbon and sulfur cycles, because they mineralize the organic matter of the anaerobic
environments. In marine sediments, 50% of organic matter is oxidized by sulfate
reduction with an equivalent or higher yield than in an aerobic process (Barton
1995). Within this group of prokaryotes, the sulfate-reducing bacteria (SRB) are the
most abundant and are widespread in natural habitats such as marine sediments,
lakes and saltwater lagoons and oil fields, as well as in the gastrointestinal tracts of
many animals, including humans. In environments with low sulfate levels, such as
bodies of freshwater, they have relevance in the mineralization of organic matter
(Muyzer and Stams 2008). Some SRB are able to survive in the presence of oxygen,
but no growth has been observed (Fournier et al. 2004). Also, SRB have industrial
(biocorrosion), environmental (bioremediation) and health (inflammation of the
intestine) implications (Bartosch et al. 2004); consequently, the SRB have been
studied extensively.
Sulfate-reducing bacteria were discovered by Martinus Willem Beijerinck in
1895 and described as the use of enrichment cultures for “sulfur fermentation”.
With his cultivation technique, he was able to isolate colonies surrounded by a black
precipitate, ferrous sulfide. Beijerinck had isolated the first sulfate-reducing bacteria
from the Dutch city canal in Delft. The morphological description of the bacterium
corresponded to curved bacilli with movement, which is the reason why it was
named Spirillum desulfuricans. Beijerinck also suggested studying other terminal
electrons acceptors, besides sulfate, and studying the distribution of these bacteria in
marine environments and soil (Voordouw 1995). SRB are chemolithotrophic
microorganisms, capable of using sulfate as the final electron acceptor in the
degradation of organic matter, a process called sulfate reduction, where hydrogen
sulfide is generated. The dissimilatory reduction of sulfate is a large-scale process
limited to SRB; however, they can also reduce other oxidized forms of sulfur such as
sulfite and thiosulfate and other inorganic compounds as nitrite or nitrate. Some SRB
are able to integrate elemental sulfur as a substrate in the respiration, and other SRB
can even respire with oxygen. SRB can grow in a sulfate-dependent manner using
hydrogen and a wide range of organic compounds, but polymeric compounds as
374
M. I. Neria-González and R. Aguilar-López