Abstract
To show the remediation of Pb-resistant bacteria to Pb polluted soil, several indices including microbial counts, soil enzyme activity, microbial community diversity and soil Pb concentration were investigated. Two Pb-resistant bacteria were filtrated and identified by previous study as Bacillus pumilus and Pseudomonas aeruginosa (GeneBank Accession No. FJ402988 and GU017676) and inoculated to soil planted with cabbages. Soil with different Pb application rates were incubated for a period of 0, 12, 24, 36, 48 days in greenhouse. Results indicated the count of bacteria in 1000 mg/kg Pb treated soil greatly affected by inoculating Pb-resistant bacteria, which was raised about 237% and 347% compared with control. Soil urease and invertase were intensified 37.9% and 65.6% after inoculation compared with control. Phosphatase activity was inhibited by inoculation of Bacillus pumilus. Catalase activity was intensified about 64.2% in 24 days incubation but decrease in the following days. Microbial community diversity analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) also proved that the samples inoculated with Pb-resistant bacteria exhibited more bands and intensity in DGGE patterns compared with uninoculated ones. For Pb-resistant bacteria inoculated samples, the reduction of Pb concentration in rhizospheric soil was 15 mg/kg at least and 42 mg/kg at most, and Pseudomonas aeruginosa showed a better tolerance to high Pb concentration and stronger remediation ability. It was concluded that remediation of Pb polluted soil can be promoted by the two Pb-resistant bacteria.
Highlights
Extensive mining and smelting have resulted in soil contamination which poses risk to human and ecological health
After the inoculation of Pb-resistant bacteria, the counts of bacteria and fungi increased about 290% and 40% than that of control when Pb concentration increased to 200 mg/kg and the decreasing trend was weakened with the increase of Pb concentration
Results indicated the quantity of culturable bacteria, fungi, actinomyces from the soil samples that were decreased from 1% - 93%, 12% - 25% and 16% - 33% respectively with the increasing of metal concentration
Summary
Extensive mining and smelting have resulted in soil contamination which poses risk to human and ecological health. Soil quality in some farmland near a mining site is getting worse and the content of heavy metal has already exceeded the third level of Environmental quality standard for soil in China (GB15618-1995) [2] Crops harvested in these areas had high concentration heavy metals and their accumulation in living tissues throughout the food chain brought a further health problem. Bioremediation is a very efficient method for cleaning up superficially contaminated soils [4] It makes use of plants and their rhizospheric microbes to degrade or immobilize pollutants in soils [5]. Soil microbes play significant roles in the process of bioremediation [6] They can absorb, transform, or degrade heavy metals, and they can reduce the mobility and bioavailability of contaminants reviewed by Wu Gang [5].
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