Effects of population density and chemical environment on the behavior of Escherichia coli in shallow temperature gradients
Effects of population density and chemical environment on the behavior of Escherichia coli in shallow temperature gradients
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DOI：
10.1088/1478-3975/8/6/063001
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发表时间：
2011-12-01
期刊：
影响因子：
2
通讯作者：
Salman, Hanna
中科院分区：
文献类型：
--
作者：
Demir, Mahmut;Douarche, Carine;Salman, Hanna
在浅温度梯度中，细菌经历的温度变化发生在很长的时间尺度上。因此，适应、代谢、化学分泌甚至基因表达等缓慢过程变得很重要。因为这些都是细胞过程，所以细胞密度是影响细菌反应的一个重要参数。我们发现存在四种具有不同行为的密度状态。在低细胞密度下，细菌不会引起其化学环境的变化；然而，它们对温度梯度的响应受到温度梯度的强烈影响。在中等细胞密度状态下，由于高温下较高的消耗率，营养物质的消耗变得显著，并导致营养物质的梯度与温度梯度相反。这导致细菌向低温方向漂移。在高细胞密度状态下，由于引诱剂的分泌，细菌之间的相互作用导致细菌的强烈局部积累。这与不同的消耗速率导致的营养梯度一起，产生了细菌密度的快速传播脉冲。这些观察结果是经典非线性种群动力学的结果。在极高的细胞密度下，可以观察到细菌生理状态的变化。在个体层面上，细菌变得冷漠。这最初表现为两种最丰富的感知受体Tsr和Tar的甲基化水平变化的结果。在更高的细胞密度下，这些受体表达水平的变化进一步加强了这种作用。
In shallow temperature gradients, changes in temperature that bacteria experience occur over long time scales. Therefore, slow processes such as adaptation, metabolism, chemical secretion and even gene expression become important. Since these are cellular processes, the cell density is an important parameter that affects the bacteria's response. We find that there are four density regimes with distinct behaviors. At low cell density, bacteria do not cause changes in their chemical environment; however, their response to the temperature gradient is strongly influenced by it. In the intermediate cell-density regime, the consumption of nutrients becomes significant and induces a gradient of nutrients opposing the temperature gradient due to higher consumption rate at the high temperature. This causes the bacteria to drift toward low temperature. In the high cell-density regime, interactions among bacteria due to secretion of an attractant lead to a strong local accumulation of bacteria. This together with the gradient of nutrients, resulted from the differential consumption rate, creates a fast propagating pulse of bacterial density. These observations are a result of classical nonlinear population dynamics. At extremely high cell density, a change in the physiological state of the bacteria is observed. The bacteria, at the individual level, become cold seeking. This appears initially as a result of a change in the methylation level of the two most abundant sensing receptors, Tsr and Tar. It is further enforced at an even higher cell density by a change in the expression level of these receptors.