Silver tolerance and silver accumulation of microorganisms from soil materials of a silver mine

Silver-tolerant microorganisms were isolated from soil materials of a silver mine to investigate their silver accumulation capacity. The objective was to understand the relationship between silver concentration and microbial growth, specifically focusing on bacterial and fungal populations. Methodologically, soil samples were enriched and cultivated under different silver nitrate concentrations, ranging from 0.01 mM to 100 mM, with subsequent isolation of around 30 silver-tolerant strains. Results indicated that the bacterial count decreased linearly with increasing silver concentration, while fungal counts remained constant up to 1 mM. At higher concentrations (10 mM and above), growth of both bacteria and fungi was inhibited. Testing revealed that bacterial isolates accumulated an average of 23 mg Ag+/g dry weight, hyphomycetes accumulated 6.7 mg/g, and yeasts had a significantly lower accumulation of 0.46 mg/g. The accumulation process for the hyphomycete with the highest capacity completed in about 30 minutes, showing minimal temperature dependence and a slight pH preference for neutrality. These findings suggest a potential binding mechanism of silver to microbial cell surfaces, highlighting the ability of certain microorganisms to tolerate and accumulate toxic metals.