Life sciences up-date. Do we need to rethink our ideas on the mechanisms of inducible processes in bacteria?

Abstract

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.