細(xì)菌也有集體記憶！這是真的嗎？
中國(guó)微生物菌種查詢網(wǎng) / 2018-12-11 09:20:09
中國(guó)微生物菌種查詢網(wǎng) 單個(gè)細(xì)菌細(xì)胞具有短暫的記憶。但是細(xì)菌群體能夠產(chǎn)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(xiàng)新的研究中，來(lái)自瑞士蘇黎世聯(lián)邦理工學(xué)院（ETH Zurich）和瑞士聯(lián)邦水生科學(xué)技術(shù)研究所（Eawag）的Roland Mathis和Martin Ackermann首次通過(guò)實(shí)驗(yàn)證實(shí)了這一點(diǎn)。相關(guān)研究結(jié)果于2016年3月9日在線發(fā)表在PNAS期刊上，論文標(biāo)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(xì)菌在隨后暴露在更高濃度鹽溶液時(shí)要比沒(méi)有經(jīng)歷類似警告事件的細(xì)菌更好地存活下來(lái)。但是，在單個(gè)細(xì)菌細(xì)胞中，這個(gè)效應(yīng)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(xiàng)新的研究中，Roland Mathis和Martin Ackermann報(bào)道了利用顯微鏡觀察新月柄桿菌（Caulobacter crescentus）獲得的這項(xiàng)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(xì)菌。
當(dāng)觀察整個(gè)新月柄桿菌群體而不是單個(gè)細(xì)菌細(xì)胞時(shí)，這些細(xì)菌似乎產(chǎn)生一種集體記憶。在遭受一種警告事件（如鹽脅迫）的細(xì)菌群體中，在這種警告事件發(fā)生幾小時(shí)后再次遭受時(shí)，它們的存活率要高于之前未遭受這種警告事件的細(xì)菌群體。利用計(jì)算建模，研究人員結(jié)合兩種因素解釋了這種現(xiàn)象。首先，鹽脅迫（salt stress）導(dǎo)致細(xì)胞分裂延遲，從而導(dǎo)致群體中每個(gè)細(xì)菌的細(xì)胞周期同步化；再者，存活概率依賴于單個(gè)細(xì)菌細(xì)胞在第二次遭受鹽脅迫時(shí)所處在細(xì)胞周期的哪個(gè)階段。因此，當(dāng)細(xì)胞周期同步化后，群體的敏感性隨著時(shí)間推移發(fā)生變化。之前遭受環(huán)境脅迫的細(xì)菌群體可能更加耐受于未來(lái)的脅迫事件，然而，它們可能有時(shí)候要比之前沒(méi)有遭受環(huán)境脅迫的細(xì)菌群體對(duì)環(huán)境脅迫更加敏感。
Martin Ackermann評(píng)論道，“如果我們理解這種集體效應(yīng)，那么它可能增強(qiáng)我們控制細(xì)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?qū)股禺a(chǎn)生耐藥性，或者用于工業(yè)生產(chǎn)過(guò)程或廢水處理廠中的細(xì)菌培養(yǎng)物的處理性能如何在動(dòng)態(tài)條件下得以維持？從人類角度而言，取決于特定的過(guò)程，它們可能是有益的，比如它們降解污染物或者將營(yíng)養(yǎng)物轉(zhuǎn)化為能量；它們也可能是有害的，尤其是如果它們能夠?qū)е录膊〉脑?。Mathis說(shuō)，對(duì)科學(xué)家們而言，還可得出另一種重要結(jié)論，“如果想要理解微生物群體的行為和命運(yùn)的話，那么分析每一個(gè)細(xì)胞有時(shí)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.