细菌也有集体记忆！这是真的吗？
中国微生物菌种查询网 / 2018-12-11 09:20:09
中国微生物菌种查询网 单个细菌细胞具有短暂的记忆。但是细菌群体能够产生一种集体记忆，从而增加它们的环境胁迫耐受性。在一项新的研究中，来自瑞士苏黎世联邦理工学院（ETH Zurich）和瑞士联邦水生科学技术研究所（Eawag）的Roland Mathis和Martin Ackermann首次通过实验证实了这一点。相关研究结果于2016年3月9日在线发表在PNAS期刊上，论文标题为“Response of single bacterial cells to stress gives rise to complex history dependence at the population level”。
暴露在中等浓度盐溶液中的细菌在随后暴露在更高浓度盐溶液时要比没有经历类似警告事件的细菌更好地存活下来。但是，在单个细菌细胞中，这个效应是短暂的：在仅仅30分钟后，它的存活率就不再依赖于它的暴露历史。
在这项新的研究中，Roland Mathis和Martin Ackermann报道了利用显微镜观察新月柄杆菌（Caulobacter crescentus）获得的这项新发现，其中新月柄杆菌是一种在淡水和海水中广泛存在的细菌。
当观察整个新月柄杆菌群体而不是单个细菌细胞时，这些细菌似乎产生一种集体记忆。在遭受一种警告事件（如盐胁迫）的细菌群体中，在这种警告事件发生几小时后再次遭受时，它们的存活率要高于之前未遭受这种警告事件的细菌群体。利用计算建模，研究人员结合两种因素解释了这种现象。首先，盐胁迫（salt stress）导致细胞分裂延迟，从而导致群体中每个细菌的细胞周期同步化；再者，存活概率依赖于单个细菌细胞在第二次遭受盐胁迫时所处在细胞周期的哪个阶段。因此，当细胞周期同步化后，群体的敏感性随着时间推移发生变化。之前遭受环境胁迫的细菌群体可能更加耐受于未来的胁迫事件，然而，它们可能有时候要比之前没有遭受环境胁迫的细菌群体对环境胁迫更加敏感。
Martin Ackermann评论道，“如果我们理解这种集体效应，那么它可能增强我们控制细菌群体的能力。”这些发现具有重大意义，比如，有助我们理解病原体如何能够对抗生素产生耐药性，或者用于工业生产过程或废水处理厂中的细菌培养物的处理性能如何在动态条件下得以维持？从人类角度而言，取决于特定的过程，它们可能是有益的，比如它们降解污染物或者将营养物转化为能量；它们也可能是有害的，尤其是如果它们能够导致疾病的话。Mathis说，对科学家们而言，还可得出另一种重要结论，“如果想要理解微生物群体的行为和命运的话，那么分析每一个细胞有时也是必需的。”
Response of single bacterial cells to stress gives rise to complex history dependence at the population level
Roland Mathis and Martin Ackermann
Most bacteria live in ever-changing environments where periods of stress are common. One fundamental question is whether individual bacterial cells have an increased tolerance to stress if they recently have been exposed to lower levels of the same stressor. To address this question, we worked with the bacterium Caulobacter crescentus and asked whether exposure to a moderate concentration of sodium chloride would affect survival during later exposure to a higher concentration. We found that the effects measured at the population level depended in a surprising and complex way on the time interval between the two exposure events: The effect of the first exposure on survival of the second exposure was positive for some time intervals but negative for others. We hypothesized that the complex pattern of history dependence at the population level was a consequence of the responses of individual cells to sodium chloride that we observed: (i) exposure to moderate concentrations of sodium chloride caused delays in cell division and led to cell-cycle synchronization, and (ii) whether a bacterium would survive subsequent exposure to higher concentrations was dependent on the cell-cycle state. Using computational modeling, we demonstrated that indeed the combination of these two effects could explain the complex patterns of history dependence observed at the population level. Our insight into how the behavior of single cells scales up to processes at the population level provides a perspective on how organisms operate in dynamic environments with fluctuating stress exposure.