polysaccharides and proteins are not typically used by them. Therefore, SRB are
very versatile with respect to the electron donors and acceptors for their growth.
Sulfate-reducing bacteria most studied are Desulfovibrio spp., which are curved
bacilli, are spiroidal bacilli and occasionally are straight bacilli, and present mobility
by polar flagella. Under stress conditions, some bacteria are polymorphic, such as
D. africanus, D. salexigens and D. gigas. Nutritionally, the cultures are easily
enriched with lactate, a reducing agent for their growth and in some cases of
vitamins. Lactate is partially oxidized to acetate for most of the species. Some strains
are capable of growing in the presence of H 2 as a source of energy and acetate plus
CO 2 or yeast extract as a source of carbon, while carbohydrates are a source unusual
of carbon. Very few members carry out a fermentative metabolism. Others are
moderate halophiles by their requirement of NaCl (20–30 g/L). Not only is sulfate
the electron acceptor, but also the sulfite and thiosulfate and in some cases nitrate are
final electron acceptors (Devereux et al. 1990; Voordouw 1995). Some bacteria have
the capacity to reduce iron (III), uranium (VI), chromium (VI), pertechnetate (VII),
selenite (VI) and arsenate (VI), but these reduction processes are not coupled to
growth (Cabrera et al. 2006; Muyzer and Stams 2008).
13.4.1 Classification and Phylogeny
During the first six decades of the last century, the knowledge of new SRB with
similar cellular characteristics but different morphologies generated serious
problems in the classification of this bacterial group. In 1936, Kluyver and Niel
gave the prospects for a natural system of classification of bacteria, as an attempt to
devise a bacterial natural classification of their own, based primarily on morphological criteria, but attaching great weight to physiological characters. Based on the
morphological and physiological criteria, the genus Desulfovibrio was established,
and “Spirillum desulfuricans”, discovered by Beijerinck, was the first species, but
with a novel name Desulfovibrio desulfuricans. Later, Campbelly and Postgate
proposed the genus Desulfotomaculum (1965). Both continued studding the Gramnegative SRB and discovered the presence of cytochrome c 3 , indicated by an
absorption band at 552–554 mμ, forming a “pyridine hemochromogen” of the
hematoheme class, observed by other investigators too. This generated a greater
understanding of Gram-negative SRB that the genus Desulfovibrio was improved
(Postgate and Campbell 1966). For 25 years, other SRB were isolated, and other
genera that appeared such as Desufobacter, Desulfobulbus, Desulfococcus,
Desulfonema,
Desulfobotulus,
Desulfobacterium,
Desulfomonile,
and
Desulfoarculus were described (Widdel and Pfennig 1984). Thermophilic Gramnegative bacteria able to reduce sulfate were classified inner of the genera
Thermodesulfomicrobium and Thermodesulfobacterium, and thermophilic Grampositive sulfate reducers were placed in Desulfotomaculum. On the other hand,
two isolate sulfate reducers from anaerobic submarine hydrothermal areas were
denominated as archaeal sulfate reducers, which were classified as Archaeoglobus
fulgidus and A. profundus. Then, three basic cell groups of SRB were proposed:
13 Heavy Metal Removal Processes by Sulfate-Reducing Bacteria
375
very versatile with respect to the electron donors and acceptors for their growth.
Sulfate-reducing bacteria most studied are Desulfovibrio spp., which are curved
bacilli, are spiroidal bacilli and occasionally are straight bacilli, and present mobility
by polar flagella. Under stress conditions, some bacteria are polymorphic, such as
D. africanus, D. salexigens and D. gigas. Nutritionally, the cultures are easily
enriched with lactate, a reducing agent for their growth and in some cases of
vitamins. Lactate is partially oxidized to acetate for most of the species. Some strains
are capable of growing in the presence of H 2 as a source of energy and acetate plus
CO 2 or yeast extract as a source of carbon, while carbohydrates are a source unusual
of carbon. Very few members carry out a fermentative metabolism. Others are
moderate halophiles by their requirement of NaCl (20–30 g/L). Not only is sulfate
the electron acceptor, but also the sulfite and thiosulfate and in some cases nitrate are
final electron acceptors (Devereux et al. 1990; Voordouw 1995). Some bacteria have
the capacity to reduce iron (III), uranium (VI), chromium (VI), pertechnetate (VII),
selenite (VI) and arsenate (VI), but these reduction processes are not coupled to
growth (Cabrera et al. 2006; Muyzer and Stams 2008).
13.4.1 Classification and Phylogeny
During the first six decades of the last century, the knowledge of new SRB with
similar cellular characteristics but different morphologies generated serious
problems in the classification of this bacterial group. In 1936, Kluyver and Niel
gave the prospects for a natural system of classification of bacteria, as an attempt to
devise a bacterial natural classification of their own, based primarily on morphological criteria, but attaching great weight to physiological characters. Based on the
morphological and physiological criteria, the genus Desulfovibrio was established,
and “Spirillum desulfuricans”, discovered by Beijerinck, was the first species, but
with a novel name Desulfovibrio desulfuricans. Later, Campbelly and Postgate
proposed the genus Desulfotomaculum (1965). Both continued studding the Gramnegative SRB and discovered the presence of cytochrome c 3 , indicated by an
absorption band at 552–554 mμ, forming a “pyridine hemochromogen” of the
hematoheme class, observed by other investigators too. This generated a greater
understanding of Gram-negative SRB that the genus Desulfovibrio was improved
(Postgate and Campbell 1966). For 25 years, other SRB were isolated, and other
genera that appeared such as Desufobacter, Desulfobulbus, Desulfococcus,
Desulfonema,
Desulfobotulus,
Desulfobacterium,
Desulfomonile,
and
Desulfoarculus were described (Widdel and Pfennig 1984). Thermophilic Gramnegative bacteria able to reduce sulfate were classified inner of the genera
Thermodesulfomicrobium and Thermodesulfobacterium, and thermophilic Grampositive sulfate reducers were placed in Desulfotomaculum. On the other hand,
two isolate sulfate reducers from anaerobic submarine hydrothermal areas were
denominated as archaeal sulfate reducers, which were classified as Archaeoglobus
fulgidus and A. profundus. Then, three basic cell groups of SRB were proposed:
13 Heavy Metal Removal Processes by Sulfate-Reducing Bacteria
375