Microbial Ecology Program, The University of Montana, Missoula, MT 59812, USA.
Appl Environ Microbiol. 2011 Jan;77(1):108-13. doi: 10.1128/AEM.01187-10. Epub 2010 Nov 5.
A novel microcalorimetric approach was used to analyze the responses of a metal-tolerant soil bacterium (Pseudomonas putida strain KT2440) to metal resistance gene deletions in cadmium-amended media. As hypothesized, under cadmium stress, the wild-type strain benefited from the resistance genes by entering the exponential growth phase earlier than two knockout strains. In the absence of cadmium, strain KT1, carrying a deletion in the main component (czcA1) of a Cd/Zn chemiosmotic efflux transporter (CzcCBA1), grew more efficiently than the wild type and released ∼700 kJ (per mole of biomass carbon) less heat than the wild-type strain, showing the energetic cost of maintaining CzcCBA1 in the absence of cadmium. A second mutant strain (KT4) carrying a different gene deletion, ΔcadA2, which encodes the main Cd/Pb efflux transporter (a P-type ATPase), did not survive beyond moderate cadmium concentrations and exhibited a decreased growth yield in the absence of cadmium. Therefore, CadA2 plays an essential role in cadmium resistance and perhaps serves an additional function. The results of this study provide direct evidence that heavy metal cation efflux mechanisms facilitate shorter lag phases in the presence of metals and that the maintenance and expression of tolerance genes carry quantifiable energetic costs and benefits.
一种新的微量热法被用于分析耐金属土壤细菌（铜绿假单胞菌 KT2440 株）对添加镉的培养基中金属抗性基因缺失的响应。正如假设的那样，在镉胁迫下，野生型菌株通过比两个敲除菌株更早地进入指数生长阶段而受益于抗性基因。在没有镉的情况下，携带 Cd/Zn 化学渗透外排转运体（CzcCBA1）主要成分（czcA1）缺失的菌株 KT1 比野生型生长效率更高，比野生型菌株释放的热量少约 700 kJ（每摩尔生物量碳），表明在没有镉的情况下维持 CzcCBA1 的能量成本。第二个携带不同基因缺失的突变菌株（KT4），缺失编码主要 Cd/Pb 外排转运体（一种 P 型 ATP 酶）的 cadA2 基因，在中等镉浓度以上不能存活，并且在没有镉的情况下生长产量降低。因此，CadA2 在镉抗性中起着重要作用，并且可能具有额外的功能。这项研究的结果提供了直接证据，证明重金属阳离子外排机制在存在金属时缩短了迟滞期，并且耐受基因的维持和表达具有可量化的能量成本和收益。
