Abstract
Conditions that impair protein folding in the Gram-negative bacterial envelope cause stress. The destabilizing effects of stress in this compartment are recognized and countered by a number of signal transduction mechanisms. Data presented here reveal another facet of the complex bacterial stress response, release of outer membrane vesicles. Native vesicles are composed of outer membrane and periplasmic material, and they are released from the bacterial surface without loss of membrane integrity. Here we demonstrate that the quantity of vesicle release correlates directly with the level of protein accumulation in the cell envelope. Accumulation of material occurs under stress, and is exacerbated upon impairment of the normal housekeeping and stress-responsive mechanisms of the cell. Mutations that cause increased vesiculation enhance bacterial survival upon challenge with stressing agents or accumulation of toxic misfolded proteins. Preferential packaging of a misfolded protein mimic into vesicles for removal indicates that the vesiculation process can act to selectively eliminate unwanted material. Our results demonstrate that production of bacterial outer membrane vesicles is a fully independent, general envelope stress response. In addition to identifying a novel mechanism for alleviating stress, this work provides physiological relevance for vesicle production as a protective mechanism.
Highlights
The capacity of bacteria to mount a multifaceted response to the wide variety of stressors encountered by these organisms in vivo and in environmental reservoirs is only recently becoming fully appreciated
Conditions that impair protein folding in the Gramnegative bacterial envelope cause stress
Data presented here reveal another facet of the complex bacterial stress response, release of outer membrane vesicles
Summary
The capacity of bacteria to mount a multifaceted response to the wide variety of stressors encountered by these organisms in vivo and in environmental reservoirs is only recently becoming fully appreciated. Multiple stress response systems monitor and respond to the condition of the envelope compartment. The phageshock-protein (Psp) system appears to respond to conditions that cause dissipation of the proton motive force, though the method of activation and function of this pathway are not yet clear (Darwin, 2005). The Bae pathway plays a role in resistance to antimicrobial compounds via regulation of multidrug transporters, and shares a number of activating signals with the Cpx response (Raffa and Raivio, 2002). Cpx monitors pili biogenesis by sensing misfolded pilin subunits, and is involved in surface attachment (Duguay and Silhavy, 2004). The sE pathway is activated in response to misfolded outer membrane proteins (OMPs) (Walsh et al, 2003; Wilken et al, 2004)
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