Rowbury R J
Department of Biology, University College London, UK.
Sci Prog. 1998;81 ( Pt 3):193-204.
It is confirmed that for a large number of inducible stress tolerance and sensitization responses in Escherichia coli, induction is associated with the secretion of components, often proteins, which can induce related responses in other organisms under normally non-inducing conditions. For most responses, the original induction is also dependent on the functioning of the extracellular agent. It is proposed that the extracellular induction components (EICs) not only induce appropriate responses in organisms in the vicinity of those challenged by the stress, but also act as extracellular alarmones. It is predicted that the switching-on of all other inducible stress tolerances and stress cross-protection and cross-sensitization responses will be found to require similar EICs produced on exposure to appropriate stresses. It is also suggested that cultures will respond to many inhibitory chemicals such as antibiotics, chlorine, other biocides and NO (and possibly to inhibitory biological agents) by producing appropriate EICs i.e. that organisms have evolved so that on exposure to any lethal challenge or a challenge that might be expected to become lethal, they produce diffusible secreted components (EIC alarmones) which both act as a warning to other potentially vulnerable organisms and prepare those organisms to resist the expected challenge. One major stress involves transfer to higher oxygen levels and it is suggested that EIC alarmones will be involved in the rapid habituation to such conditions; such EICs may function not only to induce protection against oxidative components formed as the O2 level rises, but may also be involved in induction/repression of metabolic pathways needed to accomodate to the conditions by giving the most favourable growth at high O2. It is also predicted that envelope alterations induced by environmental changes will prove to be dependent on secreted EICs. The possibility that other inducible processes, including those involving induction or repression of enzymes or pathways by changes in nutrient level, might need EICs has also been discussed. It is concluded that the evolution of EICs now allows organisms to make a meaningful response to almost all inhibitory chemical, physical and, possibly, biological agents and agencies. Also, however, it can be argued that it would be beneficial if nutrient-regulated inducible and repressible processes involving changes in enzyme levels also depended on EICs and, accordingly, in view of such advantages, evolution may have ensured that enzyme inductions and repressions commonly involve such extracellular induction components. It is essential that this be tested. Even those responses unlikely to be associated with EIC secretion (e.g., rapid and reversible processes such as chemotactic responses) may be indirectly influenced by EICs.
已证实，对于大肠杆菌中大量的诱导型应激耐受性和致敏反应，诱导作用与成分的分泌相关，这些成分通常是蛋白质，它们能够在正常非诱导条件下诱导其他生物体产生相关反应。对于大多数反应而言，最初的诱导作用也依赖于细胞外因子的功能。有人提出，细胞外诱导成分（EICs）不仅能在受到应激挑战的生物体附近诱导其他生物体产生适当反应，还能充当细胞外警报素。据预测，所有其他诱导型应激耐受性、应激交叉保护和交叉致敏反应的开启都将被发现需要在暴露于适当应激时产生类似的EICs。还有人提出，培养物会通过产生适当的EICs来应对许多抑制性化学物质，如抗生素、氯、其他杀菌剂和一氧化氮（可能还包括抑制性生物制剂），即生物体已经进化到在暴露于任何致命挑战或可能预期会变得致命的挑战时，会产生可扩散的分泌成分（EIC警报素），这些成分既能向其他潜在易受影响的生物体发出警告，又能使这些生物体做好抵抗预期挑战的准备。一种主要的应激涉及转移到更高的氧水平，有人提出EIC警报素将参与对这种条件的快速适应；此类EICs可能不仅起到诱导保护作用，防止随着氧气水平升高而形成的氧化成分，还可能参与诱导/抑制适应这些条件所需的代谢途径，以便在高氧环境下实现最有利的生长。还预测环境变化引起的包膜改变将被证明依赖于分泌的EICs。也讨论了其他诱导过程的可能性，包括那些由营养水平变化诱导或抑制酶或途径的过程，可能需要EICs。得出的结论是，EICs的进化现在使生物体能够对几乎所有抑制性化学、物理以及可能的生物制剂和因素做出有意义的反应。然而，也可以认为，如果涉及酶水平变化的营养调节诱导型和可阻遏型过程也依赖于EICs，那将是有益的，因此，鉴于这些优势，进化可能确保酶的诱导和阻遏通常涉及此类细胞外诱导成分。必须对此进行测试。即使是那些不太可能与EIC分泌相关的反应（例如趋化反应等快速且可逆的过程）也可能受到EICs的间接影响。
