Characterization of Cu-resistant bacterial communities in Cu-contaminated soils

Bacterial communities in a spoil heap in a copper mine, a forest soil with high Cu contamination, and an agricultural soil with low Cu contamination were characterized in terms of Gram-staining, plasmid frequency, pigmentation, Cu-resistance system, and predominant Cu-resistant bacterial species. Similarity existed in that the ratio of green colonies for sorbing Cu and Gram-negative bacteria increased with the increase of the Cu content of the medium regardless of the characteristics of the bacterial communities. It was found that the plasmid was not present in most of the Cu-resistant bacteria of the soils. Curesistant genera including Burkholderia, Alcaligenes, and Methylobacterium species were isolated from the Cu contaminated soils using YG agar plates treated with 2 mM Cu. Furthermore, the bacterium with the highest Cu resistance (MIC = 5.5 mm Cu) was identified as a Gram-positive bacterium Bacillus sp., though most of the Cu-resistant bacteria were Gram-negative.