據(jù)最近一篇發(fā)表于Proceedings of the National Academy of Sciences雜志的研究報(bào)告，科學(xué)家在研究枯草芽孢桿菌(Bacillus subtilis)時(shí)發(fā)現(xiàn),，細(xì)菌在受脅迫的環(huán)境中,，整個(gè)細(xì)菌群落能夠通過權(quán)衡，從而采取不同的策略生存下去,。
據(jù)作者介紹,，細(xì)菌在脅迫環(huán)境下，能夠通過開啟和關(guān)閉的某些基因來維持生存的方式,，不僅可以揭示生物系統(tǒng)間相互作用的復(fù)雜性,，還有助于經(jīng)濟(jì)學(xué)家以及政治科學(xué)家建立類似的數(shù)學(xué)模型來描述人類做決策的復(fù)雜過程。
自然界中,，細(xì)菌一般是群居生活的,，一個(gè)小小的細(xì)菌群落中細(xì)菌的總數(shù)就有可能超過地球上所有人口的100倍。許多細(xì)菌對(duì)多種極端環(huán)境（如饑餓,，毒性和放射性）的應(yīng)答往往是形成孢子,，當(dāng)環(huán)境得到改善后，孢子可以通過出芽形成正常的細(xì)菌,?？莶菅挎邨U菌可在10小時(shí)內(nèi)完成該過程，整個(gè)過程大約需要500個(gè)基因的參與,。
細(xì)菌在形成孢子的過程中,，其最終產(chǎn)物并不一定全都是孢子，在某些情況下可以進(jìn)入到另一種被稱之為“competence”的狀態(tài)中,。在這種狀態(tài),，細(xì)菌只是細(xì)胞膜發(fā)生改變，使其能夠輕易地從死亡的母細(xì)胞中吸收營(yíng)養(yǎng)物質(zhì),，像這樣,，細(xì)菌即使遇到不良環(huán)境中,，也可不通過形成孢子的形式安然度過危險(xiǎn)期。這種狀態(tài)的優(yōu)勢(shì)在于,，當(dāng)環(huán)境好轉(zhuǎn),，細(xì)菌能夠后迅速恢復(fù)到正常功能，但這種狀態(tài)的劣勢(shì)在于,，一旦環(huán)境變得更惡劣,，那么細(xì)菌將面臨更大的死亡危險(xiǎn)。
因此,，細(xì)菌在面臨不利環(huán)境時(shí),，究竟要以哪種狀態(tài)生存的選擇類似于一個(gè)著名的博弈論問題——囚徒困境(Prisoner's Dilemma)。而且對(duì)整個(gè)細(xì)菌群落來說,，這種博弈顯得更為復(fù)雜。每一個(gè)細(xì)菌必須做出決策——要么形成孢子,，要么進(jìn)入“competence”狀態(tài),。研究人員發(fā)現(xiàn)，當(dāng)細(xì)菌遭遇不利的周圍環(huán)境時(shí),，會(huì)及時(shí)發(fā)出化學(xué)信號(hào)通知其它細(xì)菌,，以讓其做好相應(yīng)的準(zhǔn)備。（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS December 7, 2009, doi: 10.1073/pnas.0912185106
Deciding fate in adverse times: Sporulation and competence in Bacillus subtilis
Daniel Schultza, Peter G. Wolynesa,1, Eshel Ben Jacoba,b,1,2 and José N. Onuchica,1,2
aCenter for Theoretical Biological Physics, University of California at San Diego, La Jolla, CA 92093-0374; and
bSchool of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv, Israel
Bacteria serve as the central arena for understanding how gene networks and proteins process information and control cellular behaviors. Recently, much effort has been devoted to the investigation of specific bacteria gene circuits as functioning modules. The next challenge is the integrative modeling of complex cellular networks composed of many such modules. A tractable integrative model of the sophisticated decision-making signal transduction system that determines the fate between sporulation and competence is presented. This model provides an understanding of how information is sensed and processed to reach an “informative” decision in the context of cell state and signals from other cells. The competence module (ComK dynamics) is modeled as a stochastic switch whose transition rate is controlled by a quorum-sensing unit. The sporulation module (Spo0A dynamics) is modeled as a timer whose clock rate is adjusted by a stress-sensing unit. The interplay between these modules is mediated via the Rap assessment system, which gates the sensing units, and the AbrB–Rok decision module, which creates an opportunity for competence within a specific window of the sporulation timer. The timer is regulated via a special repressilator-like inhibition of Spo0A* by Spo0E, which is itself inhibited by AbrB. For some stress and input signals, this repressilator can generate a frustration state with large variations (fluctuations or oscillations) in Spo0A* and AbrB concentrations, which might serve an important role in generating cell variability. This integrative framework is a starting point that can be extended to include transition into cannibalism and the role of colony organization.
