# Tellurite and selenite processing by tellurite resistant marine microbes

## TL;DR

This study explores how marine microbes process tellurite and selenite, showing that combining these elements can reduce the production of toxic volatile compounds.

## Contribution

The study reveals that mixing tellurite and selenite alters microbial metabolism, increasing precipitation and reducing toxicity.

## Key findings

- Tellurite influences selenite metabolism, reducing Se volatilization and promoting precipitation.
- Combined Se/Te processing by microbes leads to less toxic outcomes compared to single-element processes.
- Volatile Se and Te compounds like dimethylselenide are acutely toxic and must be considered in biotechnological applications.

## Abstract

Understanding microbial transformations of the group VIa/16 metalloids tellurium and selenium is important for the remediation of contaminated environments and has been proposed as a green route for Se/Te nanoparticle synthesis. We previously isolated several strains of aerobic tellurite resistant marine yeast and bacteria. Here, we explored the capability of these strains to metabolize selenite and mixtures of tellurite and selenite to quantify fate and identify volatile metabolic products. The experimental results indicate that selenite is metabolized differently than tellurite by the yeast Rhodotorula mucilaginosa and bacteria Bacillus spp. and Virgibacillus halodenitrificans. The production of volatile Se compounds appears to be positively correlated with selenite resistance. However, selenite fate, e.g., the proportion of volatilized or precipitated Se, was not predictable from tellurite resistance or fate of the same strain. Under non-aerated conditions, when cultures were provided mixtures of selenite and tellurite, tellurite strongly influenced the fate of selenite and the types of volatile products made. Tellurite in oxyanion mixtures appears to strongly inhibit Se volatilization and drive speciation to less complex Se volatiles. Mixtures boosted the production of Te and Se precipitates by Bacillus sp. strain 6A and the production of Te precipitates by Rhodotorula mucilaginosa strains 13B and decreased the production of both volatile Te and Se compounds. Dimethylselenide and dimethyltelluride are acutely toxic by inhalation and oral exposure, so understanding their production is a key consideration in any biologically based manufacture of Se/Te containing nanoparticles.

Many microbes are remarkably resistant to high concentrations of both selenite and tellurite while producing less toxic and bioavailable elemental forms, providing opportunities for the remediation of contaminated environments and green biosynthesis of Se/Te nanoparticles. The toxicity of volatile tellurite and selenite compounds produced during microbial processing may limit the development of remediation and biosynthesis technologies. The precise biochemical mechanisms governing Te and Se fate are still unclear. The data presented here demonstrate that combining Se and Te influenced the tolerance of marine microbes (Rhodotorula mucilaginosa 13B and Bacillus sp. strain 6A) to tellurite, significantly increasing precipitation as a product while limiting volatilization with the implication that combined Se/Te microbial remediation and/or nanoparticle synthesis may be less problematic than single element processes.