Xenobiotics tolerant bacteria in soils near a Pb-Zn smelter in Bulgaria as estimated via the 16S rRNA gene approach

Microbial diversity in xenobiotics polluted soils was investigated by the 16S rRNA gene approach. The samples studied were collected from the vicinity of a Pb-Zn (KCM) smelter and pesticides manufacturing plant situated in South Bulgaria. ICP-MS analyses showed that some metals such as Zn, Pb, Cu, Cd, As, Ni and Hg exceeded in high extent the maximum permission standard. Two 16S rRNA gene clone banks were constructed – KCM-B and KCM-C. The main part of the studied microbial communities consisted of members of Proteobacteria (and ) - 42 % for KCM-B and 72 % for the KCM-C sample. In both soils Proteobacteria were registered in equal content of 28 %. Acidobacteria, Holophaga, Cytophaga/Flavo-bacterium/Bacteroides, AD1 and other novel divisions were represented as well.
Most of the identified bacterial groups were closely related to bacteria inhabiting other extreme environments such as uranium mill-tailings, sulphide mines, mine drainages and dumps, metal-rich sediments, soils contaminated with polychlorinated hydrocarbons, deserts, and Antarctic permafrost. Some of the closest relatives of several identified groups were xenobiotics-degrading bacteria inhabiting a hexane-degrading biofilm, 1,2-dichloropropan transforming bacteria and phosphorous eliminating bacteria.