Microbial Transformations of Selenium Species of Relevance to Bioremediation

Abstract

b Selenium species, particularly the oxyanions selenite (SeO 3 2؊ ) and selenate (SeO 4 2؊ ), are significant pollutants in the environment that leach from rocks and are released by anthropogenic activities. Selenium is also an essential micronutrient for organisms across the tree of life, including microorganisms and human beings, particularly because of its presence in the 21st genetically encoded amino acid, selenocysteine. Environmental microorganisms are known to be capable of a range of transformations of selenium species, including reduction, methylation, oxidation, and demethylation. Assimilatory reduction of selenium species is necessary for the synthesis of selenoproteins. Dissimilatory reduction of selenate is known to support the anaerobic respiration of a number of microorganisms, and the dissimilatory reduction of soluble selenate and selenite to nanoparticulate elemental selenium greatly reduces the toxicity and bioavailability of selenium and has a major role in bioremediation and potentially in the production of selenium nanospheres for technological applications. Also, microbial methylation after reduction of Se oxyanions is another potentially effective detoxification process if limitations with low reaction rates and capture of the volatile methylated selenium species can be overcome. This review discusses microbial transformations of different forms of Se in an environmental context, with special emphasis on bioremediation of Se pollution. Since the discovery in 1954 by Pinsent that the oxidation of formate by cell suspensions of Escherichia coli requires growth medium containing molybdate and selenite, there has been a growing interest in the biochemical role of selenium in microorganisms (1). Se is an essential component of selenoamino acids, such as selenomethionine and selenocysteine (the 21st proteinogenic amino acid), that occur in certain types of prokaryotic enzymes. Indeed, the requirement for selenite in E. coli growing on formate is linked to the fact that formate dehydrogenase contains selenocysteine. Other prokaryotic enzymes that contain selenocysteine include glycine reductase in several clostridia, formate dehydrogenases in diverse prokaryotes, including Salmonella, Clostridium, and Methanococcus, as well as hydrogenases in Methanococcus and other anaerobes. In addition, other bacterial Se-dependent enzymes, in which the selenium is part of the active site molybdenum-containing cofactor, include nicotinic acid dehydrogenase and xanthine dehydrogenase, which is present in certain clostridial species (2-4).Reactions that are involved in the cycling of Se in soil, including those influenced by microbes, are diagrammatically summarized in Fig. 1 2Ϫ and was spatially separated from sulfate reduction in the environment despite the presence of substantial concentrations of sulfate where it occurred. Thus, it can be concluded that Se and S have different reductive biogeochemical cycles and appear to involve distinct populations of microorganisms.With respect to the remediation of sel...

The reduction of selenium(IV) by boreal Pseudomonas sp. strain T5-6-I – Effects on selenium(IV) uptake in Brassica oleracea

“…From the bioremediation point of view, dissimilatory selenium reduction is expected to be more important in contrast to the assimilatory reduction. This is because of the higher selenium concentrations passing through the dissimilatory pathway (Eswayah et al 2016). For this reason, especially the microorganisms utilizing the dissimilatory reduction of selenium could be used as profitable means for the remediation of selenium polluted areas (Eswayah et al 2016).…”

“…This is because of the higher selenium concentrations passing through the dissimilatory pathway (Eswayah et al 2016). For this reason, especially the microorganisms utilizing the dissimilatory reduction of selenium could be used as profitable means for the remediation of selenium polluted areas (Eswayah et al 2016). In the environment, the reduced insoluble Se 0 is considered less harmful compared to the soluble oxyanionic forms of Se(IV) and Se(VI).…”

Bacillus cereus, selenite-reducing bacterium from contaminated lake of an industrial area: a renewable nanofactory for the synthesis of selenium nanoparticles

“…Thus, the isolated bacterial strain can be exploited as a prospective, renewable, natural, nanofactory for the bacteriogenic synthesis of nanoparticles, in addition to the detoxification of selenite from the contaminated environment. Further detailed studies are envisaged on enzymatic detoxification mechanisms of metalloid reduction, other products of selenite biotransformation such as seleno-amino acids and volatile alkyl selenides; scale up for commercial production; biological activities of the produced selenium nanoparticles (Eswayah et al 2016;Nancharaiah and Lens 2015).…”

Halomonas Venusta Mediated Detoxification and Biotransformation of Selenite Into Selenium Nanoparticles Exhibiting Various Biomedical Applications

“…Being highly bioavailable selenite is taken up easily by the majority of plants and animals present in the aquatic environment and ultimately enters the human food chain posing a serious threat to the health of all the components of the food chain. These alarming conditions provoked environmental microbiologists to explore and design biological systems and tools to detoxify and bioremediate selenite from marine polluted sites which are eco-friendly and cost-effective (Higashi et al 2005;Soda et al 2012;Eswayah et al 2016).…”