Potential of tellurite resistance in heterotrophic bacteria from mining environments

Abstract

Untreated mining wastes and improper disposal of high-tech devices generate an environmental increase of bioavailable metalloids, exerting stress on autochthonous microbial populations. Tellurium is a metalloid, an element with raising economic importance; nevertheless, its interaction with living organisms is not yet fully understood. Here we characterized aerobic heterotrophic bacteria, isolated from high metal-content mining residues, able to resist/reduce tellurite into tellurium structures and to determine the presence of confirmed tellurite resistance genetic determinants in resistant strains. We identified over 50 tellurite-resistant strains, among 144 isolates, eight strains reduced tellurite to tellurium at different rates, with the concomitant production of tellurium deposits. Most tellurite resistance genes were found in strains from Bacillales, with the prevalence of genes of the ter operon. This work demonstrated that bacterial isolates, from environments with a persistent selective pressure, are potential candidates for uncovering strategies for tellurite resistance and/or production of valuable Te-containing materials.

Keywords: Bacteriology; Biogeoscience; Microbiology.

Graphical abstract

Figure 1

Mining isolation sources Visual demonstration of biologically active sediments from (A) Aljustrel, (B) Jales, and (C) Panasqueira. Summarized the description of sampled mines and samples’ general characteristics.

Figure 2

Growth in the presence of Te (IV) Specific growth rates calculated for strains (left to right): Mesorhizobium qingshengii Te58, Mesorhizobium qingshengii Te59, Cellulomonas marina 5W10, Bacillus altitudinis 3W19, Bacillus safensis 10W7, Bacillus mycoides ALJ98a, Paenibacillus tundrae ALJ98b and Paenibacillus pabuli ALJ109b. Comparison of growth in selected concentration of Te (IV), Control (no Te (IV), 1 × 10⁻⁴ M Te (IV), 2.5 × 10⁻⁴ M Te (IV), and 5 × 10⁻⁴ M Te (IV) was conducted in triplicate, with standard deviations indicated in error bars. Statistical significance is represented by symbols ∗(p ≤ 0.05), ∗∗(p ≤ 0.01) and ∗∗∗(p ≤ 0.001).

Figure 3

Tellurite depletion with environmental bacteria Tellurite depletion from liquid media, over time, for strains able to grow in liquid media with 5 × 10⁻⁴ M Te (IV). Strains (left to right): Mesorhizobium qingshengii Te58, Mesorhizobium qingshengii Te59, Cellulomonas marina 5W10, Bacillus altitudinis 3W19, Bacillus safensis 10W7, Bacillus mycoides ALJ98a, Paenibacillus tundrae ALJ98b and Paenibacillus pabuli ALJ109b. Results are presented as the result of triplicates, with standard deviations indicated in error bars.

Figure 4

SEM micrographs of tellurite reducing cells fixated on stainless steel surfaces (A) Cellulomonas marina 5W10, (B) Bacillus altitudinis 3W19, (C) Bacillus safensis 10W7, (D) Bacillus mycoides ALJ98a, (E) Paenibacillus tundrae ALJ98b,and (F) Paenibacillus pabuli ALJ109b. For images (D), (E) bar (black) = 5 μm; for images (A), (B), (C) and (F) bar (white) = 3 μm. High-density metal deposits are represented in white. EDS spectra are obtained from reads at randomly selected white segments and red arrows highlight Te detection in spectra. Inlets in SEM micrographs (white arrows) highlight organized features (described in the text).

Figure 5

Genetic organization of ter gene clusters in Bacillus strains PCR of multi-gene amplicons, identification of amplification products, and putative genetic arrangements. (A) PCR of fragment terC-telA, 1. Bacillus mycoides ALJ98a, 2. Bacillus zhangzhouensis 5W24, 3. Bacillus safensis 10W7, 4. Bacillus altitudinis 3W19 and 5. Negative control. (B and C) PCR of fragment terZ-terC: 1. Negative control, 2. Bacillus altitudinis 3W19, 3. Bacillus zhangouensis 5W24, 4. Bacillus mycoides ALJ98a and 5. Bacillus safensis 10W7. (D) Diagram representation of genetic arrangement based on sequenced and identified amplicons a to g, with abbreviated identification. Size indication based on amplicon positioning on the gel.