Spatial and temporal changes in colonization of heavy metal-tolerant bacteria in the lead-zinc tailings with different deposited history

Culturable heavy metal-tolerant bacteria in 5～10 cm and 25～30 cm layers of three lead-zinc tailings,deposited for about 10,20 and 80 years respectively,were investigated.Comparing with the campus soil,decreased total microbial population and a higher percentage of heavy metal-tolerant microorganisms was found in lead-zinc tailings.In tailings deposited for 10 years,no difference in bacterial population was found between the 5～10 cm layer and the 25～30 cm layer,but in the 20- and 80-year-old tailings,the 5～10 cm layer had 2～3 times the size of bacterial population in the 25～30 cm layer.A large population of heavy metal-tolerant bacteria was found in the lead-zinc tailings.The bacteria with high tolerance were small in size of population.Spatially,tolerant bacteria were mainly distributed in the 25～30 cm layer,however,the proportion of tolerant bacteria decreased with the increasing deposited history.Although these tailings contained a high concentration of soluble lead,but the bacteria tolerant to 10 mmol·L^-1of zinc were found in three tailings,either in the 5～10cm or 25～30 cm layers.No bacteria could resist to such a concentration of lead.However,some bacteria were found living on 0.5 mmol·L^-1 of lead and zinc.