Abstract

Soil pollution by lead (Pb) is a major health concern due to Pb toxicity. Phytoextraction could remove Pb, but this technique is limited by the low Pb mobility in soils. Pb mobility can be increased by bioaugmentation, which consists in adding selected bacteria in soil to increase Pb bioavailability. Nonetheless, many bioaugmentation and phytoextraction experiments have failed because bacterial selections did not take into account the presence of metals. Therefore, we developed a microplate assay with Pb-enriched growth media for the rapid selection of bacterial strains. Selection criteria included the ability of bacteria to grow in soils, to promote plant growth and to increase Pb availability. Results show that 100–250 µM Pb induced a decrease of production of indole acetic acid (IAA), a plant growth promotor, by up to 49% for Cupriavidus metallidurans, compared to the control without Pb. This finding implies that application in real soil conditions with C. metallidurans would have probably failed, thus strengthening the value of our selection method in the presence of Pb. By contrast, 100–250 µM Pb induced a 8.5–11-fold higher degradation of aminocyclopropane carboxylic acid (ACC) by C. metallidurans. Surprisingly, Pseudomonas putida did not degrade ACC without Pb, but degraded ACC at 100–250 µM Pb. This observation means that Pb activates ACC degradation, which should reduce plant stress because ACC is the precursor of the ethylene phytohormone. Overall, our selection method in the presence of Pb allows to reveal new bacterial properties, which would not have been disclosed by current methods that do not take into account the effect of metals. Our method allows also to test simultaneously about 200 bacterial isolates. In addition, our findings show for the first time that Pb changes the production of IAA and the degradation of ACC.

中文翻译：

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一种用Pb进行细菌选择的新方法，揭示了Pb对细菌行为的出乎意料的影响：对修复的影响

摘要

由于铅的毒性，铅对土壤的污染是主要的健康问题。植物提取可以去除铅，但是该技术受到土壤中铅迁移率低的限制。铅的迁移可以通过生物增强来提高，这包括在土壤中添加选定的细菌以提高铅的生物利用度。但是，由于细菌的选择没有考虑到金属的存在，许多生物强化和植物提取实验都失败了。因此，我们开发了一种使用富Pb的生长培养基进行微孔板测定的方法，可用于细菌菌株的快速选择。选择标准包括细菌在土壤中生长，促进植物生长和增加铅的利用率的能力。结果表明，100–250 µM Pb可使植物生长促进剂吲哚乙酸（IAA）的产量降低多达49％。与没有铅的对照相比，金属角果酸铜。这一发现表明，在实际土壤条件下使用金属利尿假单胞菌的应用可能会失败，从而增强了我们在铅存在下的选择方法的价值。相反，100-250μM铅引起的8.5-11倍由氨基环丙烷羧酸（ACC）的较高降解C. metallidurans。令人惊讶的是，恶臭假单胞菌没有Pb不会降解ACC，但是在100–250 µM Pb时会降解ACC。该观察结果表明，Pb激活了ACC降解，这将减轻植物的压力，因为ACC是乙烯植物激素的前体。总体而言，我们在Pb存在下的选择方法可以揭示新的细菌特性，而当前的方法并没有考虑到金属的影响，而这是目前尚未公开的。我们的方法还可以同时测试约200个细菌分离株。此外，我们的发现首次显示出Pb改变了IAA的产生和ACC的降解。