Geobacillus stearothermophilus V ubiE gene product is involved in the evolution of dimethyl telluride in Escherichia coli K-12 cultures amended with potassium tellurate but not with potassium tellurite

The cryptic step in the biogeochemical tellurium (Te) cycle: Indirect elementary Te oxidation mediated by manganese-oxidizing bacteria Bacillus sp. FF-1

Tellurium (Te) is a rare element within the chalcogen group, and its biogeochemical cycle has been studied extensively. Tellurite (Te(IV)) is the most soluble Te species and is highly toxic to organisms. Chemical or biological Te(IV) reduction to elemental tellurium (Te0) is generally considered an effective detoxification route for Te(IV)-containing wastewater. This study unveils a previously unnoticed Te0 oxidation process mediated by the manganese-oxidizing bacterium Bacillus sp. FF-1. This bacterium, which exhibits both Mn(II)-oxidizing and Te(IV)-reducing abilities, can produce manganese oxides (BioMnOx) and Te0 (BioTe0) when exposed to Mn(II) and Te(IV), respectively. When 5 mM Mn(II) was added after incubating 0.1 mM or 1 mM Te(IV) with strain FF-1 for 16 h, BioTe0 was certainly re-oxidized to Te(IV) by BioMnOx. Chemogenic and exogenous biogenic Te0 can also be oxidized by BioMnOx, although at different rates. This study highlights a new transformation process of tellurium species mediated by manganese-oxidizing bacteria, revealing that the environmental fate and ecological risks of Te0 need to be re-evaluated.

Microbial mechanisms to transform the super-trace element tellurium: a systematic review and discussion of nanoparticulate phases

Tellurium is a super-trace metalloid on Earth. Owing to its excellent physical and chemical properties, it is used in industries such as metallurgy and manufacturing, particularly of semiconductors and - more recently - solar panels. As the global demand for tellurium rises, environmental issues surrounding tellurium have recently aroused concern due to its high toxicity. The amount of tellurium released to the environment is increasing, and microorganisms play an important role in the biogeochemical cycling of environmental tellurium. This review focuses on novel developments on tellurium transformations driven by microbes and includes the following sections: (1) history and applications of tellurium; (2) toxicity of tellurium; (3) microbial detoxification mechanisms against soluble tellurium anions including uptake, efflux and methods of reduction, and reduced ability to cope with oxidation stress or repair damaged DNA; and (4) the characteristics and applications of tellurium nanoparticles (TeNPs) produced by microbes. This review raises the awareness of microorganisms in tellurium biogeochemical cycling and the growing applications for microbial tellurium nanoparticles.

Complete genome sequence of a tellurate reducing bacteria Sporosarcina sp. Te-1 isolated from Bohai Sea

A previously unreported tellurate reducing capacity was found in a marine bacteria Sporosarcina sp. Te-1, which was isolated from Bohai Sea, China. In this work, the complete genome of strain Te-1 was obtained using hybrid Nanopore/Illumina assemble method. A circular chromosome of 4,297,762 bp with a G + C content of 44.44 mol% was assembled. The genome harbors 4530 predicted protein-encoding genes, 71 tRNA genes, and 9 rRNA genes. Genes involved in tellurate metabolism, urea metabolism and salinity adaption were identified. These metabolic features reveal the genetic basis for the tellurate metabolism in the marine environment, which help us to further understand the marine tellurium biogeochemical cycle.

Elucidation of tellurium biogenic nanoparticles in garlic, Allium sativum, by inductively coupled plasma-mass spectrometry

BACKGROUND

Biosynthesis of Te nanoparticles may occur in higher plants exposed to Te, as reported on microorganisms. However, unambiguous observations of the biogenic nanoparticles (BgNPs) of Te in plants are lacking. Hence, in this study, we investigated the formation of insoluble BgNPs of Te in garlic (Allium sativum) as a model plant.

METHOD

We performed elemental analysis based on inductively coupled plasma-mass spectrometry (ICP-MS) technique, and obtained Te concentration and distribution in various parts of garlic. In addition, insoluble Te particles were detected by fast time-resolved ICP-MS. Direct observation of the insoluble Te particle was also conducted by scanning electron microscope (SEM) and transmission electron microscope (TEM).

RESULTS

A part of the roots and clove from Te-exposed garlic showed black coloration. Te concentrations in the black-colored parts were significantly increased compared with the non-colored parts. Transient signals of Te unique to nanoparticles were detected from the insoluble fractions of the black-colored parts. Finally, rod-shaped biogenic Te nanoparticles consisting of highly crystalline elemental Te was observed by SEM and TEM.

CONCLUSION

Our data provide new insights to the metabolic pathway of Te in higher plants for the formation of insoluble biogenic nanoparticles, which is extremely important for the detoxification of Te.

Bacterial recovery and recycling of tellurium from tellurium-containing compounds by Pseudoalteromonas sp. EPR3

AIMS

Tellurium-based devices, such as photovoltaic (PV) modules and thermoelectric generators, are expected to play an increasing role in renewable energy technologies. Tellurium, however, is one of the scarcest elements in the earth's crust, and current production and recycling methods are inefficient and use toxic chemicals. This study demonstrates an alternative, bacterially mediated tellurium recovery process.

METHODS AND RESULTS

We show that the hydrothermal vent microbe Pseudoalteromonas sp. strain EPR3 can convert tellurium from a wide variety of compounds, industrial sources and devices into metallic tellurium and a gaseous tellurium species. These compounds include metallic tellurium (Te(0)), tellurite (TeO3(2-)), copper autoclave slime, tellurium dioxide (TeO2), tellurium-based PV material (cadmium telluride, CdTe) and tellurium-based thermoelectric material (bismuth telluride, Bi2Te3). Experimentally, this was achieved by incubating these tellurium sources with the EPR3 in both solid and liquid media.

CONCLUSIONS

Despite the fact that many of these tellurium compounds are considered insoluble in aqueous solution, they can nonetheless be transformed by EPR3, suggesting the existence of a steady state soluble tellurium concentration during tellurium transformation.

SIGNIFICANCE AND IMPACT OF THE STUDY

These experiments provide insights into the processes of tellurium precipitation and volatilization by bacteria, and their implications on tellurium production and recycling.

Enhanced glutathione content allows the in vivo synthesis of fluorescent CdTe nanoparticles by Escherichia coli

The vast application of fluorescent semiconductor nanoparticles (NPs) or quantum dots (QDs) has prompted the development of new, cheap and safer methods that allow generating QDs with improved biocompatibility. In this context, green or biological QDs production represents a still unexplored area. This work reports the intracellular CdTe QDs biosynthesis in bacteria. Escherichia coli overexpressing the gshA gene, involved in glutathione (GSH) biosynthesis, was used to produce CdTe QDs. Cells exhibited higher reduced thiols, GSH and Cd/Te contents that allow generating fluorescent intracellular NP-like structures when exposed to CdCl(2) and K(2)TeO(3). Fluorescence microscopy revealed that QDs-producing cells accumulate defined structures of various colors, suggesting the production of differently-sized NPs. Purified fluorescent NPs exhibited structural and spectroscopic properties characteristic of CdTe QDs, as size and absorption/emission spectra. Elemental analysis confirmed that biosynthesized QDs were formed by Cd and Te with Cd/Te ratios expected for CdTe QDs. Finally, fluorescent properties of QDs-producing cells, such as color and intensity, were improved by temperature control and the use of reducing buffers.

Pathways and substrate specificity of DMSP catabolism in marine bacteria of the Roseobacter clade

The volatiles released by Phaeobacter gallaeciensis, Oceanibulbus indolifex and Dinoroseobacter shibae have been investigated by GC-MS, and several MeSH-derived sulfur volatiles have been identified. An important sulfur source in the oceans is the algal metabolite dimethylsulfoniopropionate (DMSP). Labelled [2H6]DMSP was fed to the bacteria to investigate the production of volatiles from this compound through the lysis pathway to [2H6]dimethylsulfide or the demethylation pathway to [2H3]-3-(methylmercapto)propionic acid and lysis to [2H3]MeSH. [2H6]DMSP was efficiently converted to [2H3]MeSH by all three species. Several DMSP derivatives were synthesised and used in feeding experiments. Strong dealkylation activity was observed for the methylated ethyl methyl sulfoniopropionate and dimethylseleniopropionate, as indicated by the formation of EtSH- and MeSeH-derived volatiles, whereas no volatiles were formed from dimethyltelluriopropionate. In contrast, the dealkylation activity for diethylsulfoniopropionate was strongly reduced, resulting in only small amounts of EtSH-derived volatiles accompanied by diethyl sulfide in P. gallaeciensis and O. indolifex, while D. shibae produced the related oxidation product diethyl sulfone. The formation of diethyl sulfide and diethyl sulfone requires the lysis pathway, which is not active for [2H6]DMSP. These observations can be explained by a shifted distribution between the two competing pathways due to a blocked dealkylation of ethylated substrates.

The bacterial response to the chalcogen metalloids Se and Te

Microbial metabolism of inorganics has been the subject of interest since the 1970s when it was recognized that bacteria are involved in the transformation of metal compounds in the environment. This area of research is generally referred to as bioinorganic chemistry or microbial biogeochemistry. Here, we overview the way the chalcogen metalloids Se and Te interact with bacteria. As a topic of considerable interest for basic and applied research, bacterial processing of tellurium and selenium oxyanions has been reviewed a few times over the past 15 years. Oddly, this is the first time these compounds have been considered together and their similarities and differences highlighted. Another aspect touched on for the first time by this review is the bacterial response in cell-cell or cell-surface aggregates (biofilms) against the metalloid oxyanions. Finally, in this review we have attempted to rationalize the considerable amount of literature available on bacterial resistance to the toxic metalloids tellurite and selenite.

Cysteine metabolism-related genes and bacterial resistance to potassium tellurite

Tellurite exerts a deleterious effect on a number of small molecules containing sulfur moieties that have a recognized role in cellular oxidative stress. Because cysteine is involved in the biosynthesis of glutathione and other sulfur-containing compounds, we investigated the expression of Geobacillus stearothermophilus V cysteine-related genes cobA, cysK, and iscS and Escherichia coli cysteine regulon genes under conditions that included the addition of K2TeO3 to the culture medium. Results showed that cell tolerance to tellurite correlates with the expression level of the cysteine metabolic genes and that these genes are up-regulated when tellurite is present in the growth medium.

Capillary electrophoretic determination of selenocyanate and selenium and tellurium oxyanions in bacterial cultures

A simple capillary zone electrophoretic method for the determination of biospherically important oxyanions of selenium (Se) and tellurium and another Se-containing anion, selenocyanate, has been developed. The method uses direct UV absorption detection. Time course experiments with time slices as short as 6 min are possible. This method's detection limits and linear range compare well with other methods involving samples containing complex biological matrices. The metalloid-containing anions examined were selenocyanate, selenite, selenate, tellurite, and tellurate. We applied this method to live cultures of two different bacteria in two different growth media in time course experiments following the changes in metalloid-containing anion concentrations. The results show that this method is a useful means of following the biological processing of these analytes in bacterial cultures.

Bacterial volatiles: the smell of small organisms

This review describes volatiles released into the air by bacteria growing on defined media. Their occurrence, function, and biosynthesis are discussed, and a total of 308 references are cited. An effort has been made to organize the compounds according to their biosynthetic origin.

Bacterial toxicity of potassium tellurite: unveiling an ancient enigma

Biochemical, genetic, enzymatic and molecular approaches were used to demonstrate, for the first time, that tellurite (TeO₃²⁻) toxicity in E. coli involves superoxide formation. This radical is derived, at least in part, from enzymatic TeO₃²⁻ reduction. This conclusion is supported by the following observations made in K₂TeO₃-treated E. coli BW25113: i) induction of the ibpA gene encoding for the small heat shock protein IbpA, which has been associated with resistance to superoxide, ii) increase of cytoplasmic reactive oxygen species (ROS) as determined with ROS-specific probe 2′7′-dichlorodihydrofluorescein diacetate (H₂DCFDA), iii) increase of carbonyl content in cellular proteins, iv) increase in the generation of thiobarbituric acid-reactive substances (TBARs), v) inactivation of oxidative stress-sensitive [Fe-S] enzymes such as aconitase, vi) increase of superoxide dismutase (SOD) activity, vii) increase of sodA, sodB and soxS mRNA transcription, and viii) generation of superoxide radical during in vitro enzymatic reduction of potassium tellurite.

Expression of the ubiE gene of Geobacillus stearothermophilus V in Escherichia coli K-12 mediates the evolution of selenium compounds into the headspace of selenite- and selenate-amended cultures

The ubiE gene of Geobacillus stearothermophilus V, with its own promoter, was cloned and introduced into Escherichia coli. The cloned gene complemented the ubiE gene deficiency of E. coli AN70. In addition, the expression of this gene in E. coli JM109 resulted in the evolution of volatile selenium compounds when these cells were grown in selenite- or selenate-amended media. These compounds were dimethyl selenide and dimethyl diselenide.

Identification of biogenic dimethyl selenodisulfide in the headspace gases above genetically modified Escherichia coli

Escherichia coli JM109 cells were modified to express the genes encoded in a 3.8-kb chromosomal DNA fragment from a metalloid-resistant thermophile, Geobacillus stearothermophilus V. Manual headspace extraction was used to collect the gases for gas chromatography with fluorine-induced sulfur chemiluminescence analysis while solid-phase microextraction was used for sample collection in gas chromatography/mass spectrometry (GC/MS) analysis. When grown in the presence of selenate or selenite, these bacteria produced both organo-sulfur and organo-selenium in the headspace gases above the cultures. Organo-sulfur compounds detected were methanethiol, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide. Organo-selenium compounds detected were dimethyl selenide and dimethyl diselenide. Two mixed sulfur-selenium compounds, dimethyl selenenyl sulfide and a chromatographically late-eluting compound, were detected. Dimethyl selenodisulfide, CH(3)SeSSCH(3), and dimethyl bis(thio)selenide, CH(3)SSeSCH(3), were synthesized and analyzed by GC/MS and fluorine-induced chemiluminescence to determine which corresponded to the late-eluting compound that was bacterially produced. CH(3)SeSSCH(3) was positively identified as the compound detected in bacterial headspace above Se-amended cultures. Using GC retention times, the boiling point of CH(3)SeSSCH(3) was estimated to be approximately 192 degrees C. This is the first report of CH(3)SeSSCH(3) produced by bacterial cultures.

Sensitivity to potassium tellurite of Escherichia coli cells deficient in CSD, CsdB and IscS cysteine desulfurases

The csdA, csdB and iscS genes encoding for cysteine desulfurase enzymatic activities in Escherichia coli were independently inactivated and potassium tellurite sensitivity, determined for each of the resulting mutant clones, was found to be iscS > csdB > csdA. Structural genes encoding for each of the wild-type cysteine desulfurases were cloned into a vector containing the regulated ara promoter and further introduced into the mutant strains. Desulfurase-deficient cells transformed with homolog or paralog desulfurase genes and grown in arabinose-amended media restored their basal tellurite resistance. While csdB gene complemented the auxotrophy of csdB and iscS mutants for nicotinic acid, the iscS gene only complemented the auxotrophy of iscS cells for thiamine. Introduction of the csdA gene into the desulfurase-deficient strains did not change tellurite resistance or nutritional requirement patterns of the recipient cells. Complementation analysis could not be performed under anaerobic conditions because the three mutants did not show tellurite hypersensitivity. These results indicate that oxidative stress is involved in tellurite toxicity in E. coli.