Highly mercury-resistant strains from different Colombian Amazon ecosystems affected by artisanal gold mining activities

Abstract

Two sites of the Colombian Amazon region with different levels of human intervention and mercury pollution were selected for the collection of samples of river and lake water, sediments, and associated forest soils. The Tarapacá region, affected mainly by barrage mining, showed low mercury concentrations, whilst in the Taraira region, affected by underground mining, there were several points with high mercury pollution levels. A collection of 72 bacterial and 10 yeast strains with different levels of mercury resistance was isolated and characterized. Most of the highly resistant bacterial strains (MIC > 40 mg L−1 HgCl2) were isolated from soil and sediment samples and belonged to either Pseudomonas (60%) or Bacillus (20%). Most of highly resistant bacterial strains were positive for the presence of the merA gene, suggesting an active mercury resistance mechanism. This was confirmed in the two most resistant strains, Pseudomonas sp. TP30 and Burkholderia contaminans TR100 (MIC = 64 and 71 mg L−1 HgCl2, respectively), which in the presence of increasing mercury concentrations expressed the merA gene at increasing levels, concomitant with a significant mercury reduction activity. Analysis of the MerA sequences present in the different isolates suggested a high gene conservation within the taxonomic groups but also several horizontal gene transfer events between taxonomically distant genera. We also observed a positive correspondence between the presence of the merA gene and the number of antibiotics to which the strains were resistant to. The most resistant strains are good candidates for future applications in the bioremediation of mercury-contaminated sites in the Amazon.Key points• Amazon sediments affected by underground gold mining have higher Hg levels.• Highly Hg-resistant isolates belonged to Pseudomonas and Bacillus genera.• TR100 and TP30 strains showed remediation potential to be used in the Amazon region. Graphical abstract

Isolation and characterization mercury-resistant bacteria from gold mining in Lebong, Bengkulu

“…Several related studies have shown that bacteria from Pseudomonas and Staphylococcus groups were also found to be MRB, as observed in the studies by [32,33]. Furthermore, various studies have been conducted regarding the application of Pseudomonas and Staphylococcus MRB as bioremediation agents, demonstrating their potential in reducing mercury contamination in environments [34].…”

Isolation and Identification of Mercury-Tolerant Bacteria LBA119 from Molybdenum-Lead Mining Soils and Their Removal of Hg2+

“…It was negative for oil hydrolysis, VP, and H 2 S. The phylogenetic tree of the strain is shown in Figure 1 d, and the 16S rDNA gene sequence comparison showed that the strain was 99% similar to strain LBA119 and strain KT758473.1 Bacillus aryabhattai. The strain LBA119 was identified as Bacillus [ 20 ].…”

Plasmid Genomes Reveal the Distribution, Abundance, and Organization of Mercury-Related Genes and Their Co-Distribution with Antibiotic Resistant Genes in Gammaproteobacteria

“…The extensive findings regarding HRGs in this study enrichened the gene sources for the exploitation of the mer-mediated functions for the Hg bioremediation [ 44 ]. Along with the fairly high diversity of HRG clusters, the transcription of HRGs can be activated in diverse ways, e.g., the merA transcription activation in Thermus thermophilus [ 45 ].…”

“…Many studies have reported finding the HRG and ARG co-distribution in various complex environments or in single microorganisms [ 20 , 21 , 24 , 45 , 46 ]. We found that there were 1368 plasmids harboring both HRGs and ARGs, representing approximately 7.30%, 79.40%, and 22.13% of all analyzed plasmids, plasmids with HRGs, and plasmids with ARGs, respectively ( Table S4 ).…”