Heavy Metal-Resistant Bacterial Communities in the Artsvanik Tailing Dump, Armenia.

Mining tailings contain high concentrations of toxic elements that can damage soil or aquatic ecosystems, reducing microbial diversity. To elucidate the bacterial community in tailings, we analyzed bacterial abundance in Cu and Mo mine tailing dump at the Artsvanik, via metagenomic and culturing. In terms of community structure, Illumina shotgun sequencing revealed that Actinomycetota exhibited the highest abundance (40.7%), followed by Pseudomonadota (22%), and Bacteroidota (10.75%). Acidobacteriota (5%), Chloroflexota (5%), Verrucomicrobia (4.25%), Planctomycetota (3.88%), Bacillota (2.8%), Gemmatimonadota (2%), and other phyla were present at low abundances. Metal-resistant bacteria in the genera Inquilinus, Methylobacterium, Sinorhizobium, Noviherbaspirillum, Variovorax, Pseudarthrobacter, Rheinheimera, Pseudomonas, Algoriphagus, Bacillus, and Niallia, were isolated from the soil and sludge samples and from weed plants in the surrounding area. For the isolated strains, the maximum tolerable concentrations of Ni(II), Cu(II), Zn(II), Cd(II), Co(II), Mo(VI), and Cr(VI) were 1-2, 1-4, 2-5, 0.3-0.6, 0.5-2, 60-68 and 0.2-0.6 mM, respectively. The strains grew in the presence of a combination of Ni(II), Cd(II), Zn(II), and Co(II) at 0.75 mM in growth medium. Owing to their high levels of resistance toward heavy metals, these isolated strains hold potential for use in bioremediation to reduce heavy-metal toxicity in contaminated environments.