**2. Bioremediation of chalcogen-contaminated environments**

The exploitation of microorganisms for the decontamination of Se- and/or Te-polluted environments is based on the capability of several bacterial strains to sequester, bioconvert or biomethylate chalcogen-oxyanions [19]. Se- or Te-species sequestration is achieved by microorganisms through either their uptake in the bacterial cell or the interaction with charged surface biomolecules [19], while the bioconversion of these oxyanions in bacteria leads to their reduction to Se0 and Te0 in the form of metalloid precipitates [19]. Further, some microorganisms can biomethylate Se or Te-oxyanions, producing volatile methyl derivatives, which can react in the atmosphere with NO3 radicals, ozone and atmospheric particles, increasing their residence times [19, 50].

Regardless, aerobic bacterial strains have been explored as pure cultures at laboratory scale for Se-bioremediation purposes, yet little work about the use of these microorganisms for large-

Among the microorganisms described for their tolerance toward Se-oxyanions, bacterial strains belonging to *Pseudomonas, Desulfovibrio, Thauera, Enterobacter, Wolinella* and *Bacillus* genera have

conditions [61, 70, 71]. Moreover, several anaerobic microorganisms have been characterized for

the bioconversion of this Se-oxyanion to the oxidation of different carbon sources, such as aliphatic (pyruvate, lactate, acetate) as well as aromatic compounds (i.e., benzoate, 3-hydroxybenzoate, 4-hydroxybenzoate) [61, 74, 75]. Nevertheless, facultative anaerobes, such as *Pseudomonas* 

reactions [17, 80–82], where glutaredoxin/thioredoxin reductase systems [19, 83] and sidero-

molecules present in the cytoplasm of bacterial cells, such as GSHs, mycothiols (MSHs), and glutaredoxins [17, 84]. Moreover, GSHs can be exported into the periplasm of Gram-negative

mostly mediated by the presence of terminal nitrite, sulfite or fumarate reductases [19, 24, 61, 66, 67, 72, 89, 90], as described for *T. selenatis* AX, *Rhizobium sullae* HCNT1 and *C. pasteurianum*, to name a few [91–93]. Further, *Geobacter sulfurreducens* [94], *Shewanella oneidensis* MR-1 [90] and

tory reduction in anoxic conditions, while among the bacterial strains able to anaerobically

observed for *Bacillus beveridgei* [22], *D. indicum* [75], *Desulfovibrio desulfuricans* [95], *E. cloacae* SLD1a-1 [96] and *Sulfospirillum barnesii* SES-3 [25, 96]. Nevertheless, fewer bacterial species (i.e., *Bacillus selenitireducens* and *Aquificales* sp.) have been described for their ability to use SeO3

Although Te does not have an essential biological role for living organisms [8], bacterial cells are able to uptake Te-oxyanions and to biomethylate and/or bioconvert them either as a decontamination strategy or during the anaerobic respiration [8, 19]. Particularly, TeO3

uptake within bacterial cells has been ascribed to the phosphate transporter in *E. coli* [97],

**2.2. Bioremediation of Te-polluted environments using bacterial pure cultures as** 

2− to SeO3

Microbial-Based Bioremediation of Selenium and Tellurium Compounds

through either detoxification strategies or anaerobic respira-

2− as terminal electron acceptor to support their growth [26, 70–73], coupling

2−, both aerobic and anaerobic microorganisms can bioconvert the highly soluble

2− detoxification occurs through several mechanisms based on Painter-type

2−-detoxification strategies exploited by microorganisms involved the interac-

2− and reactive biogenic sulfide, [86, 87], as well as the exploitation of iron

2− mainly under anoxic growth

http://dx.doi.org/10.5772/intechopen.72096

121

2− solely for detoxification purposes [70].

2− detoxification is mostly achieved by thiol

2− in the periplasm or at their cell membrane [85].

2− bioconversion during anaerobic respiration is

2− to Se0

production by further reducing SeO3

2− [26, 27].

through dissimila-

2− has been

2− as

2−

scale applications have been conducted [23].

their use of SeO4

Unlike SeO4

and reactive SeO3

tion [77–79]. SeO3

Secondary SeO3

bioconvert SeO4

**planktonic cells**

tion between SeO3

been characterized for their capability to bioconvert SeO4

*stutzeri*, showed their proficiency of bioreducing SeO<sup>4</sup>

2− [76] into Se0

phores mediate the oxyanion reduction [19, 65]. SeO3

bacteria, leading to the bioreduction of SeO3

siderophores [19, 88]. On the other hand, SeO3

2− into SeO3

*Veillonella atypica* [94] showed high proficiency in bioreducing SeO<sup>3</sup>

terminal electron acceptor as compared to those using SeO4

2−, a high yield of Se0
