The Golden Activity of Lysinibacillus sphaericus: New Insights on Gold Accumulation and Possible Nanoparticles Biosynthesis

Abstract

Power struggles surrounding the increasing economic development of gold mining give rise to severe environmental and social problems. Two new strains of Lysinibacillus sphaericus were isolated from an area of active alluvial gold mining exploitation at El Bagre, Antioquia. The absorption capacity of these strains and some of the L. sphaericus Microbiological Research Center (CIMIC) collection (CBAM5, OT4b.31, III(3)7) were evaluated by spectrophotometry according to a calibration gold curve of HAuCl₄^- with concentrations between 0 µg/mL and 100 µg/mL. Bioassays with living biomass were carried out with an initial gold concentration of 60 µg/mL. Their sorption capacity was evident, reaching percentages of gold removal between 25% and 85% in the first 2 h and 75% to 95% after 48 h. Biosynthesis of possible gold nanoparticles (AuNPs) in assays with living biomass was also observed. Metal sorption was evaluated using scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) analysis. The sorption and fabrication capacity exhibited by the evaluated strains of L. sphaericus converts this microorganism into a potential alternative for biomining processes, especially those related to gold extraction.

Keywords: Lysinibacillus sphaericus; SEM; gold; mining; nanoparticles; sorption.

Figure 1

Phylogenetic tree for Lysinibacillus sphaericus with the two new strains isolated, MCB1 and MCB2.

Figure 2

Bioassay in living cells with the L. sphaericus (a) CBAM5 as an individual strain, (b) CIMIC collection (CBAM5, OT4b.31, III(3)7) in a mix, (c) MCB1 and (d) MCB2 alone, and (e) mix with MCB1 and MCB2. The concentration of HAuCl₄⁻ evaluated was 60 µg/mL in minimum salt medium. Graphs show deviation standard for each time evaluated.

Figure 3

Bioassays of possible formation of gold nanoparticles with living cells for the strains (a) CBAM5 alone, (b) mix of MCB1 and MCB2 and, (c) control after 48 h. The numbers in the flasks are the replicates for each bioassay.

Figure 3

Bioassays of possible formation of gold nanoparticles with living cells for the strains (a) CBAM5 alone, (b) mix of MCB1 and MCB2 and, (c) control after 48 h. The numbers in the flasks are the replicates for each bioassay.

Figure 4

SEM images with SEI (secondary electrons) and BEC (Backscattered electrons) for bioassays with living cells of Lysinibacillus sphaericus (a) CBAM5 and (b) energy-dispersive X-ray spectroscopy (EDS) analysis; (c) mix of CIMIC collection strains (CBAM5, OT4b.31, III(3)7) with (d) EDS analysis. Additionally, L. sphaericus (e) strain MCB1 alone with its respective (f) EDS analysis and (g) MCB2 also with (h) EDS analysis. Similarly, the (i) mix between MCB1 and MCB2 and (j) EDS analysis.

Figure 4

SEM images with SEI (secondary electrons) and BEC (Backscattered electrons) for bioassays with living cells of Lysinibacillus sphaericus (a) CBAM5 and (b) energy-dispersive X-ray spectroscopy (EDS) analysis; (c) mix of CIMIC collection strains (CBAM5, OT4b.31, III(3)7) with (d) EDS analysis. Additionally, L. sphaericus (e) strain MCB1 alone with its respective (f) EDS analysis and (g) MCB2 also with (h) EDS analysis. Similarly, the (i) mix between MCB1 and MCB2 and (j) EDS analysis.

Figure 5

SEM and EDS analysis maps for samples of the mix between Lysinibacillus sphaericus MCB1 and MCB2 prepared in resin. Slides of 70 nm show cells (a,b) in different sporulation stages and in (c) a vegetative cell.