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Chapter 21. Geomicrobiology of Selenium and Tellurium

Chapter 21. Geomicrobiology of Selenium and Tellurium

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Geomicrobiology



21.3 TOXICITY OF SELENIUM AND TELLURIUM

Both selenium and tellurium are toxic when present in excess, but the minimum toxic doses vary

depending on the organism. As mentioned in Section 21.2, some plants accumulate selenium to the

extent of 1.5–2 g kg−1 dry weight of tissue (Stadtman, 1974). They usually grow in arid environments with unusually high concentrations of selenium in the soil. In the Kesterson National Wildlife

Refuge in California, where extensive selenium intoxication of wild animals has been observed,

selenate concentrations of 1.8–18 µM (0.14–1.4 ppm) have been reported, contrasted with normal

concentrations of ∼1.3–21.1 nM in the San Joaquin River, ∼0.4–1.3 nM in the Sacramento River,

and <0.2 nM in San Francisco Bay, all located in California (Zehr and Oremland, 1987). These

normal concentrations are below minimum inhibitory concentrations (MICs) of selenate [Se(VI)]

for three selenium-sensitive strains of bacteria from the same general area in California. Their

MICs were found to range from 0.78 to 1.56 mM for selenate and from 1.56 to 25 mM for selenite

[Se(IV)]. Selenium-resistant bacteria from the Kesterson National Wildlife Refuge exhibited MICs

of 50 to >200 mM selenate and selenite (Burton et al., 1987). By contrast, both selenium-resistant

and selenium-sensitive organisms from these same sites in California exhibited MICs for tellurate in

the range of 0.03–1 mM and for tellurite in the range of 0.03–4 mM (Burton et al., 1987).

Selenium and tellurium resistance appears to be regulated by different genes. In Escherichia

coli, tellurium resistance appears to be mediated by the arsenical ATPase efflux pump. The genetic

determinants for this pump reside on resistance plasmid R773 (Turner et al., 1992). Higher forms

of life appear to be relatively more sensitive to Se than bacteria, although they require Se as a

nutritional trace element. Biochemically, Se toxicity appears to be the result of superoxide or H2O2

production in excess of antioxidant production by a cell. A similar mechanism may be the basis for

Te toxicity (see references 31, 35, and 41 cited by Guzzo and Dubow, 2000).



21.4 BIOOXIDATION OF REDUCED FORMS OF SELENIUM

Some inorganic forms of selenium have been reported to be oxidizable by microorganisms.

Micrococcus selenicus isolated from mud (Breed et al., 1948), a rod-shaped bacterium isolated

from soil and thought to be autotrophic (Lipman and Waksman, 1923), and a purple bacterium

(Sapozhnikov, 1937) were observed to oxidize Se0 to SeO2–

4 . A strain of Bacillus megaterium from

2–

topsoil in a river alluvium was found to oxidize Se0 to SeO2–

3 and traces of SeO 4 . Red selenium

was more readily attacked than gray selenium (Sarathchandra and Watkinson, 1981). Dowdle

and Oremland (1998) observed elemental selenium oxidation in soil slurries that was inhibited

by autoclaving the slurry or by addition of formalin, azide, 2,4-dinitrophenol, or the antibiotics

chloramphenicol + tetracycline or cycloheximide + nystatin. Se0 oxidation in the slurries was

enhanced by addition of sulfide, acetate, or glucose, suggesting that sulfur-oxidizing autotrophs and

heterotrophs were involved in the oxidation.

Acidithiobacillus ferrooxidans has been shown to oxidize copper selenide (CuSe) to cupric copper

(Cu2+) and elemental selenium (Se0) (Torma and Habashi, 1972). The reaction may be written as

CuSe + 2H+ + 0.5O2 → Cu2+ + Se0 + H2O



(21.4)



21.5 BIOREDUCTION OF OXIDIZED SELENIUM COMPOUNDS

Various inorganic selenium compounds have been found to be reduced anaerobically by some

microorganisms. Crude cell extract of Micrococcus lactilyticus (also known as Veillonella lactilyticus) has been shown to reduce selenite but not selenate to Se0, and Se0 to HSe−. The reductant was

hydrogen (H2 ) (Woolfolk and Whiteley, 1962). Cell extracts from strains of Desulfovibrio desulfuricans and Clostridium pasteurianum were also found to reduce selenite with hydrogen. The enzyme

hydrogenase mediated electron transfer from hydrogen in these reactions (Woolfolk and Whiteley,



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1962). A variety of other bacteria, actinomycetes, and fungi have been shown to reduce selenate and

selenite to Se0 (Bautista and Alexander, 1972; Lortie et al., 1992; Stolz and Oremland, 1999; Tomei

et al., 1992; Zalokar, 1953). The bacteria include Pseudomonas stutzeri, Wolinella succinogenes,

and Micrococcus sp. Acidithiobacillus ferrooxidans is able to reduce the red form of Se0 to H2Se

anaerobically, albeit in small amounts (Bacon and Ingledew, 1989).

A relatively recently discovered bacterium, Thauera selenatis, can grow anaerobically with selenate or nitrate as terminal electron acceptor (Macy et al., 1993; Rech and Macy, 1992). In the

absence of nitrate, it reduces selenate to selenite (DeMoll-Decker and Macy, 1993). The reductases

for selenate and nitrate in this organism are distinct enzymes with different pH optima. Thus in

contrast to the response of a selenate-reducing enrichment culture (Steinberg et al., 1992), nitrate

does not inhibit selenate reduction by T. selenatis. Indeed, when present together, both selenate and

nitrate are reduced simultaneously, with selenate reduced to elemental selenium (DeMoll-Decker

and Macy, 1993). The selenate reductase in this organism, which catalyzes the reduction of selenate

to selenite, is found in the periplasm, whereas its nitrate reductase, which catalyzes the reduction of

nitrate to nitrite, is found in its cytoplasmic membrane (Rech and Macy, 1992), Selenate reductase

is a metalloprotein containing Mo, Fe, acid-labile sulfur, and a cytochrome b subunit (Schroeder

et al., 1997). Nitrite reductase is found in the periplasm of T. selenatis and plays a role in selenite

reduction, besides catalyzing nitrite reduction (DeMoll-Decker and Macy, 1993). This explains why

T. selenatis produces elemental selenium in the presence of nitrate, but selenite in its absence.

Selenite does not support growth of T. selenatis (DeMoll-Decker and Macy, 1993).

A selenite reductase enzyme has been obtained from the fungus Candida albicans (Falcone

and Nickerson, 1963; Nickerson and Falcone, 1963). It reduces selenite to Se0. A characterization

of the enzyme has shown that it requires a quinone, a thiol compound (e.g., glutathione), a pyridine

nucleotide (NADP), and an electron donor (e.g., glucose 6-phosphate) for activity. Electron transfer

between NADP and quinone is probably mediated by flavin mononucleotide in this system. It is

2–

possible that this enzyme is part of an assimilatory SeO2–

4 and SeO 3 reductase system. How this

enzyme compares with that in T. selenatis remains to be established.

Sulfurospirillum barnesii (formerly Geospirillum barnesii, also called strain SES-3) (Oremland

et al., 1994; Stolz et al., 1999) is another bacterium that can reduce selenate to elemental selenium.

Cells of this organism grew with lactate as carbon and energy source and selenate as terminal electron acceptor, which was reduced to selenite. As with Thauera selenatis, resting cells of Ssp. barnesii but not growing cells were able to reduce selenite to Se0 (Oremland et al., 1994). One important

difference between Ssp. barnesii and T. selenatis is that Ssp. barnesii is able to use a much wider

range of reducible anions as terminal electron acceptors than T. selenatis (Stolz and Oremland,

1999). Ssp. barnesii can reduce selenate and nitrate simultaneously whether pregrown on selenate

or nitrate, consistent with the observation that selenate reductase is constitutive in this organism

(Oremland et al., 1999).

Two newly discovered selenate reducers, both gram-positive bacteria, are Bacillus arsenicoselenatis and B. selenitireducens (Switzer Blum et al., 1998). The first forms spores but the second

does not. Both were isolated from anoxic muds from Mono Lake, California, which is alkaline,

hypersaline, and arsenic-rich. B. arsenicoselenatis reduces selenate to selenite whereas B. selenitireducens reduces selenite to elemental selenium as forms of anaerobic respiration. In coculture,

the two strains together can reduce selenate to elemental selenium. Both strains can reduce arsenate

as well as selenate (Switzer Blum et al., 1998). Sulfurospirillum barnesii and B. arsenicoselenatis

can reduce selenate and nitrate simultaneously, but unlike the selenate reductase in Ssp. barnesii,

that in B. arsenicoselenatis is not constitutive because it does not appear in nitrate-grown cells

(Oremland et al., 1999). Therefore, in order for B. arsenicoselenatis to reduce selenate and nitrate

simultaneously, it has to be grown in the presence of a mixture of the two electron acceptors.

A moderately halophilic selenate reducer was isolated from Dead Sea (Israel) sediment. It

reduced selenate to selenite and elemental selenium. It is a gram-negative organism and has been

named Selenihalanaerobacter shriftii (Switzer Blum et al., 2001). When it respires on glycerol or



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glucose, it forms acetate and CO2. Nitrate and trimethylamine N-oxide could serve as alternative

electron acceptors, but reduced forms of sulfur, nitrite, arsenate, fumarate, or dimethylsulfoxide

could not.

All previously mentioned selenate- and selenite-reducing bacteria belong to the domain Bacteria.

Recently, a hyperthermophilic member of the domain Archaea capable of respiring organotrophically on selenate was isolated from a hot spring near Naples, Italy (Huber et al., 2000) (see also

Chapter 14). Its name is Pyrobaculum arsenaticum. It reduces selenate to elemental selenium.

Previously isolated P. aerophilum (Völkl et al., 1993) was found capable of respiring organotrophically on selenate and selenite and autotrophically on selenate with H2 as electron donor (Huber

et al., 2000). Elemental selenium was the reduction product.

In most studies of bacterial reduction of selenate and selenite, elemental selenium (red form),

when formed, is usually found to be a major, if not the only, product. This is noteworthy because

sulfate and sulfite cannot be directly reduced to S0 but are reduced to H2S without intermediate formation of S0. Yet selenium and sulfur are members of the same chemical family. The implication is

that enzymatic mechanisms of reduction for oxidized forms of these two elements are different. To

date, none of the true selenate respirers have been found capable of sulfate respiration, which could

be related to the significantly higher energy yield in selenate respiration (∆G′, −15.53 kcal mol−1 e−1)

than in sulfate respiration (∆G′, 0.10 kcal mol−1 e−1) (Newman et al., 1998). It must be noted, however, that Desulfovibrio desulfuricans subsp. aestuarii has been found to reduce nanomolar but not

millimolar quantities of selenate to selenite (Zehr and Oremland, 1987). Sulfate inhibited reduction of selenate, suggesting but not proving that the mechanism of sulfate and selenate reduction

in this case may be a common one. As Zehr and Oremland (1987) pointed out, when sulfate is

being reduced to H2S in the absence of selenate, some of the H2S formed may subsequently reduce

biogenically formed selenite chemically to Se0. They found that in nature, the sulfate reducer can

reduce selenate only if the ambient sulfate concentration is <4 mM. Hockin and Gadd (2003) found

that in mixed biofilms, Desulfomicrobium norvegicum could reduce selenite that diffused into the

biofilm with H2S it produced anaerobically by reduction of sulfate, resulting in the formation of S0

and Se0. This reaction was abiotic and can be formulated as follows:

+

0

0

3HS− + SeO2–

4 + 5H → 3S + Se + 4H2O



(21.5)



The sulfur and selenium precipitated within the biofilm as nanometer-sized selenium–sulfur granules. By contrast, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter

shriftii can form nanospheres consisting exclusively of Se0 when reducing selenite enzymatically

(Oremland et al., 2004).

Whereas selenate and selenite reduction by the previously described organisms resulted in extracellular deposition of Se0, intracellular deposition of Se0 has been observed with some other organisms. Chromatium vinosum can deposit Se0 intracellularly as a result of an interaction of H2Se,

which is produced by Desulfovibrio desulfuricans in selenate reduction in coculture with Chr.

vinosum. The Se0 is stored in the form of globules in the Chr. vinosum cells (Nelson et al., 1996).

Rhodobacter spheroides deposited red Se0 in or on its cells when it reduced selenate and selenite

(Van Fleet-Stadler et al., 2000). Ralstonia metallidurans CH34 can reduce selenite to red Se0, which

it stores in its cytoplasm and occasionally in its periplasm (Roux et al., 2001).



21.5.1



OTHER PRODUCTS OF SELENATE AND SELENITE REDUCTION



In Escherichia coli, a significant portion of selenite reduced during glucose metabolism is deposited

as Se0 on its cell membrane but not in its cytoplasm (Gerrard et al., 1974), and another portion is

incorporated as selenide in organic compounds such as selenomethionine (Ahluwalia et al., 1968).

Some soil microbes reduce selenate or selenite to dimethylselenide [(CH3)2Se] at elevated selenium



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concentrations (Kovalskii et al., 1968; Fleming and Alexander, 1972; Alexander, 1977; Doran and

Alexander, 1977). Other volatile selenium compounds may also be formed, their relative quantities

depending on reaction conditions (Reamer and Zoller, 1980). The compounds include dimethyl

diselenide [(CH3)2Se2] and dimethyl selenone [(CH3)2SeO2].

Some fungi have been found to be effective in forming methylated selenium compounds (Barkes and

Fleming, 1974). Alternaria alternata isolated from seleniferous water from a sample series collected

from evaporation ponds at the Kesterson Reservoir, Lost Hills, and Peck Ranch in California formed

dimethylselenide more rapidly from selenate and selenite than from selenium sulfide (SeS2) or various organic Se compounds. Methionine, a known biochemical methyl donor, and methylcobalamin, a

known methyl carrier in biochemical transmethylation, stimulated dimethylselenide formation by the

fungus (Thompson-Eagle et al., 1989). Crude cell extracts and a supernatant fraction from the fungus

Pichia guillermondi after centrifugation at 144,000g reduced selenite but not selenate (Bautista and

Alexander, 1972). In a mechanism proposed by Reamer and Zoller (1980), all methylated forms of

selenium arise by methylation of selenite and subsequent reductions and, where needed, by additional

methylation of the methylated products. Dimethylselenone is viewed as a precursor of dimethylselenide,

whereas methylselenide [(CH3)SeH] and (CH3)SeOH are viewed as precursors of dimethyldiselenide.

The archaeon Methanococcus voltae has been found to be able to use dimethylselenide [(CH3)2Se]

as a source of Se required for its growth. Demethylation in this instance involved a corrinoid protein

and two methyltransferases (Niess and Klein, 2004).



21.5.2



SELENIUM REDUCTION IN THE ENVIRONMENT



Bacterial reduction of selenate and selenite has been detected in situ, especially in environments

with significant soluble selenium. In the Kesterson National Wildlife Refuge in California, Maiers

et al. (1988) reported that 4% of water samples, 92% of sediment samples, and 100% of the soil

samples they collected exhibited microbial selenium reduction. Of 100 mg selenate per liter, up

to 75% was reduced to red Se0, the rest to selenite. In the interstitial water of core samples from a

wastewater evaporation pond in Fresno, California, selenate removal was stimulated by H2 and the

2–

addition of acetate, and inhibited by O2, NO 3– , MnO2, CrO2–

4 , and WO 4 , but not by the addition of

2–

2–

SO 4 , MoO 4 , or FeOOH (Oremland et al., 1989). At other sites in California and also in Nevada,

Steinberg and Oremland (1990) found measurable selenate-reducing activity in surficial sediment

samples from bodies of freshwater to waters with salinities of 250 g L−1 but not 320 g L−1. Nitrate,

nitrite, molybdate, and tungstate added separately to samples from the agricultural drains were

inhibitory to different extents. Sulfate partially inhibited the reduction of selenate in a sample

from a freshwater site but not in one from a site with water having a salinity of 60 g L−1. These

differences are likely reflections of differences in the type of selenate reducers in the different

samples and therefore of differences in mechanisms of selenate reduction. Additional studies in the

agricultural drainage region of western Nevada revealed a selenate turnover rate of 0.04–1.8 h−1

at ambient Se oxyanion concentrations (13–455 nM). Rates of removal of selenium oxyanions

ranged from 14 to 155 µmol m−2 per day (Oremland et al., 1991). The formation of elemental Se has

a potential for selenium immobilization in soil and sediment under anaerobic conditions. Owing

to the possibility of Se0 reoxidation under aerobic conditions, remobilization may occur. However,

such reoxidation has been found to be a slow process compared to microbial selenate reduction

(Dowdle and Oremland, 1998).

A recent study of selenate-respiring bacteria detected in culture enrichments with sediments from

water bodies in Chennai, India, and New Jersey, United States, revealed the presence of a diverse

group of bacteria classifiable with Gammaproteobacteria, Deltaproteobacteria, Deferribacteres,

and Chrysiogenetes (Narasingarao and Häggblom, 2007).

Methylation of selenium in aquatic environments has also been observed (e.g., Chau et al., 1976;

Frankenberger and Karlson, 1992, 1995). This activity has a potential for Se removal from polluted



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soils and waters. Ranjard et al. (2002) demonstrated transmethylation of different forms of selenium

with bacterial thiopurine methyltransferase in a strain of Escherichia coli, DH10B, acting on selenate, selenite, (methyl)selenocysteine, and selenomethionine.

Ecologically, anaerobic reduction of selenate and selenite to selenium (Se0) represents a respiratory, energy-conserving process in some microorganisms and serves to detoxify the immediate

environment for all organisms as long as anaerobic conditions are maintained. Selenium volatilization serves as a permanent detoxification process in water, soils, and sediments, and can occur

aerobically, although in at least one instance it was more effective anaerobically (Frankenberger and

Karlson, 1995).



21.6



SELENIUM CYCLE



The existence of a selenium cycle in nature was suggested by Shrift (1964). However, some of the

details of this cycle are still obscure. The ultimate source of selenium must be igneous rocks, but

whether microbes play a role in mobilizing the selenium from selenium-containing minerals is

unknown. Similarly, little is known about the role that microbes play in mobilizing selenium in soil

and sediment. Such an activity, when it occurs, is of great importance in understanding and controlling selenium pollution, as has occurred, for instance, in the Kesterson National Wildlife Refuge in

California. The source of selenium in that case appears to be the drainage of irrigation water applied

to farmland in the San Joaquin Valley. The irrigation water leached the selenium from the soil.

This drainage has been collecting in the wildlife refuge. Different processes in selenium cycling in

wetlands include redox reactions involving selenium, methylation and volatilization of selenium,

organic and inorganic complexation of selenium, precipitation and dissolution of Se-containing

minerals, and sorption and desorption of ionic species of selenium (Masscheleyn and Patrick, 1993).

The known biochemical steps of a selenium cycle are shown in Figure 21.1.



21.7 BIOOXIDATION OF REDUCED FORMS OF TELLURIUM

Microbial oxidation of reduced forms of tellurium has so far not been reported. This may mean

that this process does not occur in nature, but it is more likely that so far it has not been sought by

investigators. Its geomicrobial importance is likely to be limited because the natural occurrence of

tellurium is much rarer than that of selenium (see Section 21.1).

Organic selenium



b

(CH3)2Se

or

(CH3)2Se2



b



SeO42−



a



?

Se2−



SeO32−

b



b, c, ?

d



b, d



e



Se0



f



CuSe



FIGURE 21.1 The selenium cycle. (a) Escherichia coli, (b) bacteria, (c) actinomycetes, (d) fungi, (e)

Micrococcus lactilyticus, (f) Acidithiobacillus ferrooxidans. (See also Doran JW, Alexander M, Appl Environ

Microbiol, 33, 31–37, 1977.)



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21.8 BIOREDUCTION OF OXIDIZED FORMS OF TELLURIUM

Microbial reduction of tellurates and tellurites to elemental tellurium (Te0) and dimethyltelluride

[(CH3)2Te] has been reported (Woolfolk and Whiteley, 1962; Silverman and Ehrlich, 1964; Nagai,

1965; Bautista and Alexander, 1972; Trutkoet al., 2000; Klonowska et al., 2005; Csotonyi et al.,

2006; Baesman et al., 2007). Trutko et al. (2000) presented evidence that in some gram-negative

bacteria the respiratory chain was involved in tellurite reduction. The tellurite was reduced to tellurium crystallites, which appeared in the periplasmic space or on the outer or inner surface of the

plasma membrane. The makeup of the respiratory chain differed to some extent among the different

bacterial cultures tested. Klonowska et al. (2005) found that although Shewanella oneidensis was

able to reduce selenite and tellurite anaerobically, the electron transport pathway to the two electron

acceptors diverged upstream from tetracytochrome c, CymA.

Baesman et al. (2007) found that Bacillus selenitireducens and Sulfurospirillum barnesii

produced Te0 in the form of nanocrystals when respiring on tellurate or tellurite. With B. selenitireducens, Te 0 was deposited in the form of nanorods on the surface of the cells, which subsequently formed clusters, called shards, and rosettes. Nanorods also appeared in the bulk phase.

Some crystals in the form of nanorods that aggregated into shard-like nanocrystals also formed

inside the cells. Ssp. barnesii deposited Te 0 as irregularly shaped nanospheres (∼20 nm diameter) frequently attached to the cell surface, which coalesced into larger clusters (500–1000 nm

diameter). Nanospheres were also observed inside the cells. A question arises whether the difference in morphologies of the Te 0 nanocrystals is somehow related to a difference in the gramstaining properties of these two organisms, B. selenitireducens being gram-positive whereas

Ssp. barnesii being gram-negative. This difference in gram reactivity may reflect a difference in

organization of their respective electron transport systems, as is probably the case, for instance,

in Mn(II)-oxidation and Mn(IV)-reduction by gram-positive and gram-negative bacteria

(see Sections 17.5 and 17.6).

The fungus Penicillium sp. has been found to produce (CH3)2Te from several inorganic tellurium

compounds, provided only that reducible selenium compounds were also present (Fleming and

Alexander, 1972). The amount of dialkyltelluride formed was related to the relative concentrations

of Se and Te in the medium. Microbial reduction of oxidized forms of tellurium may represent

detoxification reactions rather than a form of respiration, but this needs further investigation.



21.9



SUMMARY



Selenium, although a very toxic element, is nutritionally required by some bacteria, plants, and animals. Microorganisms have been described that can oxidize reduced selenium compounds. At least

one, Acidithiobacillus ferrooxidans, can use selenide in the form of CuSe as a sole source of energy,

oxidizing the compound to elemental selenium (Se0) and Cu2+. Oxidized forms of inorganic selenium compounds can be reduced by microorganisms, including members of the domains Bacteria

and Archaea, and Fungi. Selenate and selenite may be reduced to one or more of the following:

Se0, H2Se, dimethylselenide [(CH3)2Te], dimethyl diselenide [(CH3)2Se2], and dimethyl selenone

[(CH3)2SeO2]. The reductions are enzymatic and in some bacteria represent a form of respiration.

The microbial interactions with various forms of selenium contribute to a selenium cycle in nature.

Microbial selenate and selenite reduction to elemental selenium in soil and sediment is a form of

selenium immobilization that is potentially reversible. Microbial selenate and selenite reduction

to volatile forms of selenium in soil, sediment, and water columns of bodies of water is a form of

selenium removal that is permanent.

Tellurium occurs in such low concentrations in nature that it does not seem geomicrobially

important. Nevertheless, microbial reduction of tellurate and tellurite to elemental tellurium (Te0)

and dimethyltelluride [(CH3)2Te] has been observed. Microbial oxidation of tellurides has so far not

been reported.



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REFERENCES

Ahluwalia GS, Saxena YR, Williams HH. 1968. Quantitative studies on selenite metabolism in Escherichia

coli. Arch Biochem Biophys 124:79–84.

Alexander M. 1977. Introduction to Soil Microbiology. 2nd ed. New York: Wiley.

Andreesen JR, Ljungdahl LG. 1973. Formate dehydrogenase of Clostridium thermoaceticum: Incorporation

of selenium-75, and the effects of selenite, molybdate, and tungstate on the enzyme. J Bacteriol

116:869–873.

Bacon M, Ingledew WJ. 1989. The reductive reactions of Thiobacillus ferrooxidans on sulfur and selenium.

FEMS Microbiol Lett 58:189–194.

Baesman SM, Bullen TD, Dewald J, Zhang D, Curran S, Islam FS, Beveridge TJ, Oremland RS. 2007.

Formation of tellurium nanocrystals during anaerobic growth of bacteria that use Te oxyanions as respiratory electron acceptors. Appl Environ Microbiol 73:2135–2143.

Barkes L, Fleming RW. 1974. Production of dimethylselenide gas from inorganic selenium by eleven fungi.

Bull Environ Contam Toxicol 12:308–311.

Bautista EM, Alexander M. 1972. Reduction of inorganic compounds by soil microorganisms. Soil Sci Soc Am

Proc 36:918–920.

Breed RS, Murray EGD, Smith NR. 1948. Bergey’s Manual of Determinative Bacteriology. 6th ed. Baltimore,

MD: Williams & Wilkins.

Burton GA Jr., Giddings TH, DeBrine P, Fall R. 1987. High incidence of selenite-resistant bacteria from a site

polluted with selenium. Appl Environ Microbiol 53:185–188.

Chau YK, Wong PTS, Silverberg BA, Luxon PL, Bengert GA. 1976. Methylation of selenium in the aquatic

environment. Science 192:1130–1131.

Combs GF Jr., Scott ML. 1977. Nutritional interrelationships of vitamin E and selenium. BioScience

27:467–473.

Csotonyi JT, Stackebrandt E, Yurkov V. 2006. Anaerobic respiration on tellurate and other metalloids in bacteria from hydrothermal vent fields in the eastern Pacific Ocean. Appl Environ Microbiol 72:4950–4956.

DeMoll-Decker H, Macy JM. 1993. The periplasmic nitrate reductase of Thauera selenatis may catalyze the

reduction of selenite to elemental selenium. Arch Microbiol 160:241–247.

Doran JW, Alexander M. 1977. Microbial transformation of selenium. Appl Environ Microbiol 33:31–37.

Dowdle PR, Oremland RS. 1998. Microbial oxidation of elemental selenium in soil slurries and bacterial cultures. Environ Sci Technol 32:3749–3755.

Duerre P, Andreesen JR. 1982. Selenium-dependent growth and glycine fermentation by Clostridium purinolyticum. J Gen Microbiol 128:1457–1466.

Enoch HG, Lester RL. 1972. Effects of molybdate, tungstate, and selenium compounds on formate dehydrogenase and other enzymes in Escherichia coli. J Bacteriol 110:1032–1040.

Falcone G, Nickerson WJ. 1963. Reduction of selenite by intact yeast cells and cell-free preparations.

J Bacteriol 85:754–762.

Fleming RW, Alexander M. 1972. Dimethyl selenide and dimethyl telluride formation by a strain of Penicillium.

Appl Microbiol 24:424–429.

Frankenberger WT, Karlson U. 1992. Dissipation of soil selenium by microbial volatilization. In: Adriano DC,

ed. Biogeochemistry of Trace Metals. Boca Raton, FL: Lewis Publishers, pp. 365–381.

Frankenberger WT, Karlson U. 1995. Soil management factors affecting volatilization of selenium from dewatered sediments. Geomicrobiol J 12:265–277.

Gerrard TL, Telford JN, Williams HH. 1974. Detection of selenium deposits in Escherichia coli by electron

microscopy. J Bacteriol 119:1057–1060.

Guzzo J, Dubow MS. 2000. A novel selenite- and tellurite-inducible gene in Escherichia coli. Appl Environ

Microbiol 66:4972–4978.

Hockin SL, Gadd GM. 2003. Linked redox precipitation of sulfur and selenium under anaerobic conditions by

sulfate-reducing bacterial biofilms. Appl Environ Microbiol 69:7063–7072.

Huber R, Sacher M, Vollmann A, Huber H, Rose D. 2000. Respiration of arsenate and selenate by hyperthermophilic archaea. Syst Appl Microbiol 23:305–314.

Klonowska A, Heulin T, Vermeglio A. 2005. Selenite and tellurite reduction by Shewanella oneidensis. Appl

Microbiol 71:5607–5609.

Kovalskii VV, Ermakov VV, Letunova SV. 1968. Geochemical ecology of microorganisms in soils with different selenium content. Mikrobiologiya 37:122–139.

Lansche AM. 1965. Tellurium. In: Mineral Facts and Problems. Washington, DC: Bureau of Mines, Department

of the Interior, pp. 935–939.



CRC_7906_Ch021.indd 534



10/22/2008 4:14:41 PM



Geomicrobiology of Selenium and Tellurium



535



Lester RL, DeMoss JA. 1971. Effects of molybdate and selenite on formate and nitrate metabolism in

Escherichia coli. J Bacteriol 105:1006–1014.

Lipman JG, Waksman SA. 1923. The oxidation of selenium by a new group of autotrophic microorganisms.

Science 57:60.

Lortie L, Gould WD, Rajan S, McCready RGL, Cheng J-J. 1992. Reduction of selenate and selenite to elemental selenium by a Pseudomonas stutzeri isolate. Appl Environ Microbiol 58:4042–4044.

Macy JM, Rech S, Auling G, Dorsch M, Stackebrandt E, Sly L. 1993. Thauera selenatis gen. nov. sp. nov.,

a member of the beta-subclass of Proteobacteria with a novel type of anaerobic respiration. Int J Syst

Bacteriol 43:135–142.

Maiers DT, Wichlacz PL, Thompson DL, Bruhn DF. 1988. Selenate reduction by bacteria from a selenium-rich

environment. Appl Environ Microbiol 54:2591–2593.

Masscheleyn PH, Patrick WH Jr. 1993. Biogeochemical processes affecting selenium cycling in wetlands.

Environ Toxicol Chem 12:2235–2243.

Mertz W. 1981. The essential trace elements. Science 213:1332–1338.

Miller WJ, Neathery MW. 1977. Newly recognized trace mineral elements and their role in animal nutrition.

BioScience 27:674–679.

Nagai S. 1965. Differential reduction of tellurite by growing colonies of normal yeasts and respiration deficient

mutants. J Bacteriol 90:220–222.

Narasingarao P, Häggblom MM. 2007. Identification of anaerobic selenate-respiring bacteria from aquatic

sediments. Appl Environ Microbiol 73:3519–3527.

Nelson DC, Casey WH, Sison JD, Mack EE, Ahmad A, Pollack JS. 1996. Selenium uptake by sulfuraccumulating bacteria. Geochim Cosmochim Acta 60:3531–3539.

Newman DK, Ahmann D, Morel FMM. 1998. A brief review of microbial arsenate respiration. Geomicrobiol J

15:255–268.

Nickerson WJ, Falcone G. 1963. Enzymatic reduction of selenite. J Bacteriol 85:763–771.

Niess UM, Klein A. 2004. Dimethylselenide demethylation is an adaptive response to selenium deprivation in

the archeon Methanococcus voltae. J Bacteriol 186:3640–3648.

Oremland RS, Herbel MJ, Switzer Blum J, Langley S, Beveridge TJ, Ajayan PM, Sutto T, Ellis AV, Curran S.

2004. Structural and spectral features of selenium nanospheres produced by Se-respiring bacteria. Appl

Environ Microbiol 70:52–60.

Oremland RS, Hollibaugh JT, Maest AS, Presser TS, Miller LB, Cuthberson CW. 1989. Selenate reduction to

elemental selenium by anaerobic bacteria in sediments and culture: Biogeochemical significance of a

novel sulfate-independent respiration. Appl Environ Microbiol 55:2333–2343.

Oremland RS, Steinberg NA, Presser TS, Miller LG. 1991. In situ bacterial selenate reduction in the agricultural drainage system of western Nevada. Appl Environ Microbiol 57:615–617.

Oremland RS, Switzer Blum J, Burns Bindi A, Dowdle PR, Herbel M, Stolz JF. 1999. Simultaneous reduction of nitrate and selenate by cell suspensions of selenium-respiring bacteria. Appl Environ Microbiol

65:4385–4392.

Oremland RS, Switzer Blum J, Culbertson CW, Visscher PT, Miller LG, Dowdle P, Strohmaier FE. 1994.

Isolation, growth, and metabolism of an obligately anaerobic, selenate-respiring bacterium, strain SES-3.

Appl Environ Microbiol 60:3011–3019.

Patrick R. 1978. Effects of trace metals in the aquatic ecosystem. Am Sci 66:185–191.

Pinsent J. 1954. The need for selenite and molybdate in the coli-aerogenes group of bacteria. Biochem J

57:10–16.

Ranjard L, Prigent-Combaret C, Nazaret S, Cournoyer B. 2002. Methylation of inorganic and organic selenium

by the bacterial thiopurine methyltransferase. J Bacteriol 184:3146–3149.

Rapp G Jr. 1972. Selenium: Element and geochemistry. In: Fairbridge RW, ed. The Encyclopedia of

Geochemistry and Environmental Sciences. Encyclopedia of Earth Science Series, Vol. IVA. New York:

Van Nostrand Reinhold, pp. 1079–1080.

Reamer DC, Zoller WH. 1980. Selenium biomethylation products from soil and sewage. Science 208:500–502.

Rech S, Macy JM. 1992. The terminal reductases from selenate and nitrate respiration in Thauera selenatis are

two distinct enzymes. J Bacteriol 174:7316–7320.

Rosenfeld I, Beath OA. 1964. Selenium, Geobotany, Biochemistry, Toxicity, and Nutrition. New York: Academic

Press.

Rotruck JT, Pope AL, Ganther HE, Swanson AB, Hafman DG, Hoekstra WG. 1973. Selenium: Biochemical

role as a component of glutathione peroxidase. Science 179:588–590.

Roux M, Sarret G, Pignot-Paintrand I, Fontecave M, Coves J. 2001. Mobilization of selenite by Ralstonia metallidurans CH34. Appl Environ Microbiol 67:769–773.



CRC_7906_Ch021.indd 535



10/22/2008 4:14:41 PM



536



Geomicrobiology



Sapozhnikov DI. 1937. The substitution of selenium for sulfur in the photoreduction of carbonic acid by purple

sulfur bacteria. Mikrobiologiya 6:643–644.

Sarathchandra SU, Watkinson JH. 1981. Oxidation of elemental selenium to selenite by Bacillus megaterium.

Science 211:600–601.

Schroeder I, Rech S, Krafft T, Macy JM. 1997. Purification and characterization of the selenate reductase from

Thauera selenatis. J Biol Chem 272:23765–23768.

Shrift A. 1964. Selenium in nature. Nature (London) 201:1304–1305.

Shum AD, Murphy JC. 1972. Effects of selenium compounds on formate metabolism and coincidence of

selenium-75 incorporation and formic dehydrogenase activity in cell-free preparations of Escherichia

coli. J Bacteriol 110:447–449.

Silverman MP, Ehrlich HL. 1964. Microbial formation and degradation of minerals. Adv Appl Microbiol

6:153–206.

Stadtman RC. 1974. Selenium biochemistry. Science 183:915–922.

Steinberg NA, Blum JS, Hochstein L, Ormland RS. 1992. Nitrate is a preferred electron acceptor for growth of

freshwater selenate-respiring bacteria. Appl Environ Microbiol 58:426–428.

Steinberg NA, Oremland RS. 1990. Dissimilatory selenate reductase potentials in a diversity of sediment types.

Appl Environ Microbiol 56:3550–3557.

Stolz JF, Ellis DJ, Switzer Blum J, Ahmann D, Oremland RS, Lovley DR. 1999. Sulfurospirillum barnesii

sp. nov. and Sulfurospirillum arsenophilus sp. nov., new members of the Sulfurospirillum clade of the

ε-Proteobacteria. Int J Syst Bacteriol 49:1177–1180.

Stolz JF, Oremland RS. 1999. Bacterial respiration of arsenic and selenium. FEMS Microbiol Rev

23:615–627.

Switzer Blum J, Burns Bindi A, Buzzelli J, Stolz JG, Oremland RS. 1998. Bacillus arsenicoselenatis, sp. nov.,

and Bacillus selenitireducens, sp. nov.: Two haloalkaliphiles from Mono Lake, California that respired

oxyanions of selenium and arsenic. Arch Microbiol 171:19–30.

Switzer Blum J, Stolz JF, Oren A, Oremland RS. 2001. Selenihalanaerobacter shriftii gen nov., spec. nov., a

halophilic anaerobed from Dead Sea sediments that respire selenate. Arch Microbiol 175:208–219.

Thompson-Eagle ET, Frankenberger WT Jr., Karlson U. 1989. Volatilization of selenium by Alternaria alternata. Appl Environ Microbiol 55:1406–1413.

Tomei FA, Barton LL, Lemansky CL, Zocco TG. 1992. Reduction of selenate and selenite to elemental selenium by Wolinella succinogenes. Can J Microbiol 38:1328–1333.

Torma AE, Habashi F. 1972. Oxidation of copper(II) selenide by Thiobacillus ferrooxidans. Can J Microbiol

18:1780–1781.

Trutko SM, Akimenko VK, Suzina NE, Anisimova LA, Shlyapnikov MG, Baskunov BP, Duda VI, Boronin

AM. 2000. Involvement of the respiratory chain of gram-negative bacteria in the reduction of tellurite.

Arch Microbiol 173:178–186.

Turner RJ, Hou Y, Weiner JH, Taylor DE. 1992. The arsenical ATPase efflux pump mediates tellurite resistance.

J Bacteriol 174: 3092–3094.

Van Fleet-Stadler V, Chasteen TG, Pickering IJ, George GN, Prince RC. 2000. Fate of selenate and selenite

metabolized by Rhodobacter sphaeroides. Appl Environ Microbiol 66:4849–4853.

Völkl P, Huber R, Drobner E, Rachel R, Burggraf S, Trincone A, Stetter KO. 1993. Pyrobaculum aerophilum

sp. nov., a novel nitrate-reducing hyperthermophilic archaeum. Appl Environ Microbiol 59:2918–2926.

Woolfolk CA, Whiteley HR. 1962. Reduction of inorganic compounds with molecular hydrogen by Micrococcus

lactilyticus. I. Stoichiometry with compounds of arsenic, selenium, tellurium, transition and other elements. J Bacteriol 84:647–658.

Yamamoto I, Saiki T, Liu S-M, Ljungdahl LG. 1983. Purification and properties of NADP-dependent formate dehydrogenase from Clostridium thermoaceticum, a tungstate-selenium protein. J Biol Chem

258:1826–1832.

Zalokar M. 1953. Reduction of selenite by Neurospora. Arch Biochem Biophys 44:330–337.

Zehr JP, Oremland RS. 1987. Reduction of selenate to selenide by sulfate-respiring bacteria: Experiments with

cell suspensions and estuarine sediments. Appl Environ Microbiol 53:1365–1369.



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22 Geomicrobiology

of Fossil Fuels

22.1 INTRODUCTION

Although much of the organic carbon in the biosphere is continually recycled, a very significant

amount has become trapped in special sedimentary formations, where it is inaccessible to mineralization by microbes until it becomes reexposed to water through natural causes or human intervention. Microbial mineralization of such reexposed organic carbon also depends on the access

to suitable terminal electron acceptors, that is, oxygen in air in the case of aerobes, and inorganic

electron acceptors in the case of facultative or anaerobic microbes. The trapped organic carbon

exists in various forms. The degree of its chemically reduced state is related to the length of time

it has been trapped and any secondary changes that it has undergone during this time. Some of

this trapped carbon has value as a fuel, a source of energy for industrial and other human activity,

and is exploited for this purpose. Because of the great age of this material, it is known as fossil

fuel. The remainder of the trapped carbon is chiefly kerogen and bitumen, some of which can be

converted to fuel by human intervention. Fossil fuels include methane gas, natural gas (which is

largely methane), petroleum, oil shale, coal, and peat. They are generally considered to have had a

microbial origin (Ourisson et al., 1984).



22.2



NATURAL ABUNDANCE OF FOSSIL FUELS



A major portion of the total carbon at the Earth’s surface is in the form of carbonate (Figure 22.1). It

represents a major sink for carbon. The other sink is the trapped organic carbon that is not directly

accessible for microbial mineralization. The carbonate carbon is not an absolute sink unless it is

deeply buried because it is in a steady-state relationship with dissolved carbonate/bicarbonate and

atmospheric CO2, which in turn are in a steady-state relationship with organic carbon in living and

dead biomass. The passage of carbon from one compartment into another is under biological control

(Figure 22.1; Fenchel and Blackburn, 1979).



22.3



METHANE



Methane at atmospheric pressure and ambient temperature is a colorless, odorless, and flammable

gas. Because its autoignition temperature is 650°C, it does not catch fire spontaneously. It is sparingly soluble in water (3.5 mL per 100 mL of water) but readily soluble in organic solvents, including

liquid hydrocarbons. It may have an abiotic or biogenic origin. Biogenic accumulations of methane

may occur in nature when it is formed in consolidated sediment from which it cannot readily escape.

In some deep-ocean sediments under conditions of high pressure and low temperature, methane

accumulations are found in the form of methane hydrates (Kvenvolden, 1988; Haq, 1999). A special,

mixed community of certain members of the Archaea and Bacteria living very close to methane

hydrate has been detected in the forearc basin of the Nankai Trough off the east coast of Japan by

Reed et al. (2002) and in solid gas hydrates in the Gulf of Mexico by Mills et al., 2005.

Bioformation of methane comes about when organic matter in the sediment is undergoing anaerobic microbial breakdown in the absence of significant quantities of alternative terminal electron

537



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Geomicrobiology



Atmospheric CO2

6.4 × 1017 g C

a



Dissolved

CO2

3.8 × 1019 g C



r



r

a



8.3 × 1017 g C



Dissolved

organics



a



Living biomass



e,d



1.5 × 1018 g C



a

m



a,m

s



d



Organic carbon

in sediments and

soils



Limestone and other

fixed carbonates



3.5 × 1018 g C



1.8 × 1022 g C



b

Trapped organic

carbon:

natural gas, coal,

petroleum,

kerogen, and bitumen

2.5 × 1022 g C



FIGURE 22.1 Microbial and physical processes contributing to carbon transfer among different compartments in the biosphere. a, Microbial assimilation; b, burial; d, decomposition; e, excretion; m, microbial mineralization; r, respiration; s, sedimentation. (Quantitative estimates from Fenchel T, Blackburn TH, Bacteria

and Mineral Cycling, Academic Press, London, U.K., 1979; Bowen HJM, Environmental Chemistry of the

Elements, Academic Press, London, U.K., 1979.)



acceptors such as nitrate, Fe(III), Mn(IV), or sulfate. If gas pressure due to methane builds up sufficiently in anaerobic lake or coastal sediment, it may escape in the form of large gas bubbles that

break at the water surface to release their methane into the atmosphere (Martens, 1976; Zeikus,

1977). In marshes, escaping methane may be ignited (by biogenic phosphene?) to burn as the socalled will-o’-the-wisps.

Many of the methane accumulations on Earth are of biogenic origin. Methane may occur in association with peat, coal, and oil deposits, or independent of them. That which occurs in association

with coal and oil was probably microbially generated in the early stages of their formation, although

some may have been formed abiotically in later diagenetic phases. Methane associated with coal

deposits can be the cause of serious mine explosions when accidentally ignited. Such methane is

called coal damp by coal miners.

Biogenic methane formation is a unique biochemical process that appears to have arisen very

early in the evolution of life. Indeed, the methanogenesis that results from the microbial reduction



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