Indole-3-acetic acid improves Escherichia coli’s defences to stress
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Indole-3-acetic acid (IAA) is a ubiquitous molecule playing regulatory roles in many living organisms. To elucidate the physiological changes induced by IAA treatment, we used Escherichia coli K-12 as a model system. By microarray analysis we found that 16 genes showed an altered expression level in IAA-treated cells. One-third of these genes encode cell envelope components, or proteins involved in bacterial adaptation to unfavourable environmental conditions. We thus investigated the effect of IAA treatment on some of the structural components of the envelope that may be involved in cellular response to stresses. This showed that IAA-treated cells had increased the production of trehalose, lipopolysaccharide (LPS), exopolysaccharide (EPS) and biofilm. We demonstrated further that IAA triggers an increased tolerance to several stress conditions (heat and cold shock, UV-irradiation, osmotic and acid shock and oxidative stress) and different toxic compounds (antibiotics, detergents and dyes) and this correlates with higher levels of the heat shock protein DnaK. We suggest that IAA triggers an increased level of alert and protection against external adverse conditions by coordinately enhancing different cellular defence systems.
KeywordsTrehalose DnaK LPS EPS Biofilm Stress response
We wish to thank S. Adhya and the E. coli Genetic Stock Centre for providing bacterial strains. We acknowledge A. Spena and J. Beckwith for their helpful discussion, C. Sole and R. Vito for technical assistance. This work was supported by the European Union INCO-DEV SONGLINES grant, project ICA4-CT-2001-10059 and by Italian MIUR, project FIRB RBNE0118BHE. We are grateful to P. De Luca (BioGEM Ariano Irpino-AV) and S. Crispi (IGB-Naples) who carried out the arrays hybridization and scanning.
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