Maintaining a healthy SPANC balance through regulatory and mutational adaptation.
Stress protection is an important but costly contributor to bacterial survival. Two distinct forms of environmental protection share a common cost and a significant species-wide variability. Porin-mediated outer membrane permeability and the RpoS-controlled general stress response both involve a trade-off between self-preservation and nutritional competence, called the SPANC balance. Interestingly, different Escherichia coli strains exhibit distinct settings of the SPANC balance. It is tilted towards high stress resistance and a restricted diet in some isolates whereas others have broader nutritional capability and better nutrient affinity but lower levels of resistance. Growth- or stress-related selective pressures working in opposite directions (antagonistic pleiotropy) result in polymorphisms affecting porins and RpoS. Consequently, these important cellular components are present at distinct concentrations in different isolates. A generalized hypothesis to explain bacterial adaptation, based on the SPANC investigations, is offered. A holistic approach to bacterial adaptation, involving a gamut of regulation and mutation, is likely to be the norm in broadening the capabilities of a species. Indeed, there is unlikely to be a standard regulatory setting typical for all members of a species. Gene regulation provides a limited fine control for maintaining the right level of adaptation in a particular niche but mutational changes provide the coarse control for adaptation between the species-wide environments of free-living bacteria.
Ferenci
Thomas
T
School of Molecular and Microbial Biosciences, The University of Sydney, NSW 2006, Australia. tferenci@mail.usyd.edu.au
D000222:Adaptation, Physiological / Q000502:physiology*; D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000502:physiology; D002463:Cell Membrane Permeability; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D009154:Mutation; D018272:Porins / Q000502:physiology; D012808:Sigma Factor / Q000502:physiology
D001426:Bacterial Proteins; D018272:Porins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria