Laboratorio de Microbiología Molecular y Biotecnología Ambiental, Departamento de Química and Center for Nanotechnology and Systems Biology, Universidad Técnica Federico Santa María, Valparaíso, Chile.
PLoS One. 2011 Mar 14;6(3):e17555. doi: 10.1371/journal.pone.0017555.
Mercury-polluted environments are often contaminated with other heavy metals. Therefore, bacteria with resistance to several heavy metals may be useful for bioremediation. Cupriavidus metallidurans CH34 is a model heavy metal-resistant bacterium, but possesses a low resistance to mercury compounds.
METHODOLOGY/PRINCIPAL FINDINGS: To improve inorganic and organic mercury resistance of strain CH34, the IncP-1β plasmid pTP6 that provides novel merB, merG genes and additional other mer genes was introduced into the bacterium by biparental mating. The transconjugant Cupriavidus metallidurans strain MSR33 was genetically and biochemically characterized. Strain MSR33 maintained stably the plasmid pTP6 over 70 generations under non-selective conditions. The organomercurial lyase protein MerB and the mercuric reductase MerA of strain MSR33 were synthesized in presence of Hg(2+). The minimum inhibitory concentrations (mM) for strain MSR33 were: Hg(2+), 0.12 and CH(3)Hg(+), 0.08. The addition of Hg(2+) (0.04 mM) at exponential phase had not an effect on the growth rate of strain MSR33. In contrast, after Hg(2+) addition at exponential phase the parental strain CH34 showed an immediate cessation of cell growth. During exposure to Hg(2+) no effects in the morphology of MSR33 cells were observed, whereas CH34 cells exposed to Hg(2+) showed a fuzzy outer membrane. Bioremediation with strain MSR33 of two mercury-contaminated aqueous solutions was evaluated. Hg(2+) (0.10 and 0.15 mM) was completely volatilized by strain MSR33 from the polluted waters in presence of thioglycolate (5 mM) after 2 h.
CONCLUSIONS/SIGNIFICANCE: A broad-spectrum mercury-resistant strain MSR33 was generated by incorporation of plasmid pTP6 that was directly isolated from the environment into C. metallidurans CH34. Strain MSR33 is capable to remove mercury from polluted waters. This is the first study to use an IncP-1β plasmid directly isolated from the environment, to generate a novel and stable bacterial strain useful for mercury bioremediation.
受汞污染的环境通常会受到其他重金属的污染。因此，具有多种重金属抗性的细菌可能对生物修复有用。铜绿假单胞菌 CH34 是一种模式抗重金属细菌，但对汞化合物的抗性较低。
方法/主要发现：为了提高菌株 CH34 对无机和有机汞的抗性，通过双杂交交配将提供新型 merB、merG 基因和其他 mer 基因的 IncP-1β 质粒 pTP6 引入该细菌。对转导子铜绿假单胞菌菌株 MSR33 进行了遗传和生化表征。在非选择性条件下，菌株 MSR33 在超过 70 代的时间内稳定地维持质粒 pTP6。在存在 Hg(2+)的情况下，菌株 MSR33 合成了有机汞裂解酶蛋白 MerB 和汞还原酶 MerA。菌株 MSR33 的最小抑制浓度（mM）为：Hg(2+)，0.12 和 CH(3)Hg(+)，0.08。在指数期添加 0.04 mM 的 Hg(2+)对菌株 MSR33 的生长速率没有影响。相比之下，在指数期添加 Hg(2+)后，亲本菌株 CH34 立即停止细胞生长。在暴露于 Hg(2+)期间，未观察到 MSR33 细胞形态发生变化，而暴露于 Hg(2+)的 CH34 细胞显示出模糊的外膜。评估了菌株 MSR33 对两种受汞污染的水溶液的生物修复。在存在巯基乙醇（5 mM）的情况下，MSR33 在 2 小时内将污染水中的 0.10 和 0.15 mM Hg(2+)完全挥发。
结论/意义：通过将直接从环境中分离的质粒 pTP6 掺入铜绿假单胞菌 CH34 中，生成了广谱抗汞菌株 MSR33。菌株 MSR33 能够从污染水中去除汞。这是首次使用直接从环境中分离的 IncP-1β 质粒来生成用于汞生物修复的新型稳定细菌株的研究。
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