細菌也有集體記憶！這是真的嗎？
中國微生物菌種查詢網 / 2018-12-11 09:20:09
中國微生物菌種查詢網 單個細菌細胞具有短暫的記憶。但是細菌群體能夠產生一種集體記憶，從而增加它們的環(huán)境脅迫耐受性。在一項新的研究中，來自瑞士蘇黎世聯(lián)邦理工學院（ETH Zurich）和瑞士聯(lián)邦水生科學技術研究所（Eawag）的Roland Mathis和Martin Ackermann首次通過實驗證實了這一點。相關研究結果于2016年3月9日在線發(fā)表在PNAS期刊上，論文標題為“Response of single bacterial cells to stress gives rise to complex history dependence at the population level”。
暴露在中等濃度鹽溶液中的細菌在隨后暴露在更高濃度鹽溶液時要比沒有經歷類似警告事件的細菌更好地存活下來。但是，在單個細菌細胞中，這個效應是短暫的：在僅僅30分鐘后，它的存活率就不再依賴于它的暴露歷史。
在這項新的研究中，Roland Mathis和Martin Ackermann報道了利用顯微鏡觀察新月柄桿菌（Caulobacter crescentus）獲得的這項新發(fā)現(xiàn)，其中新月柄桿菌是一種在淡水和海水中廣泛存在的細菌。
當觀察整個新月柄桿菌群體而不是單個細菌細胞時，這些細菌似乎產生一種集體記憶。在遭受一種警告事件（如鹽脅迫）的細菌群體中，在這種警告事件發(fā)生幾小時后再次遭受時，它們的存活率要高于之前未遭受這種警告事件的細菌群體。利用計算建模，研究人員結合兩種因素解釋了這種現(xiàn)象。首先，鹽脅迫（salt stress）導致細胞分裂延遲，從而導致群體中每個細菌的細胞周期同步化；再者，存活概率依賴于單個細菌細胞在第二次遭受鹽脅迫時所處在細胞周期的哪個階段。因此，當細胞周期同步化后，群體的敏感性隨著時間推移發(fā)生變化。之前遭受環(huán)境脅迫的細菌群體可能更加耐受于未來的脅迫事件，然而，它們可能有時候要比之前沒有遭受環(huán)境脅迫的細菌群體對環(huán)境脅迫更加敏感。
Martin Ackermann評論道，“如果我們理解這種集體效應，那么它可能增強我們控制細菌群體的能力?！边@些發(fā)現(xiàn)具有重大意義，比如，有助我們理解病原體如何能夠對抗生素產生耐藥性，或者用于工業(yè)生產過程或廢水處理廠中的細菌培養(yǎng)物的處理性能如何在動態(tài)條件下得以維持？從人類角度而言，取決于特定的過程，它們可能是有益的，比如它們降解污染物或者將營養(yǎng)物轉化為能量；它們也可能是有害的，尤其是如果它們能夠導致疾病的話。Mathis說，對科學家們而言，還可得出另一種重要結論，“如果想要理解微生物群體的行為和命運的話，那么分析每一個細胞有時也是必需的?！?br />
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.