Outer Membrane Vesicle Production Facilitates LPS Remodeling and Outer Membrane Maintenance in Salmonella during Environmental Transitions.
Abstract
The ability of Gram-negative bacteria to carefully modulate outer membrane (OM) composition
is essential to their survival. However, the asymmetric and heterogeneous structure
of the Gram-negative OM poses unique challenges to the cell's successful adaption
to rapid environmental transitions. Although mechanisms to recycle and degrade OM
phospholipid material exist, there is no known mechanism by which to remove unfavorable
lipopolysaccharide (LPS) glycoforms, except slow dilution through cell growth. As
all Gram-negative bacteria constitutively shed OM vesicles (OMVs), we propose that
cells may utilize OMV formation as a way to selectively remove environmentally disadvantageous
LPS species. We examined the native kinetics of OM composition during physiologically
relevant environmental changes in Salmonella enterica, a well-characterized model
system for activation of PhoP/Q and PmrA/B two-component systems (TCSs). In response
to acidic pH, toxic metals, antimicrobial peptides, and lack of divalent cations,
these TCSs modify the LPS lipid A and core, lengthen the O antigen, and upregulate
specific OM proteins. An environmental change to PhoP/Q- and PmrA/B-activating conditions
simultaneously induced the addition of modified species of LPS to the OM, downregulation
of previously dominant species of LPS, greater OMV production, and increased OMV diameter.
Comparison of the relative abundance of lipid A species present in the OM and the
newly budded OMVs following two sets of rapid environmental shifts revealed the retention
of lipid A species with modified phosphate moieties in the OM concomitant with the
selective loss of palmitoylated species via vesiculation following exposure to moderately
acidic environmental conditions. IMPORTANCE: All Gram-negative bacteria alter the
structural composition of LPS present in their OM in response to various environmental
stimuli. We developed a system to track the native dynamics of lipid A change in Salmonella
enterica serovar Typhimurium following an environmental shift to PhoP/Q- and PmrA/B-inducing
conditions. We show that growth conditions influence OMV production, size, and lipid
A content. We further demonstrate that the lipid A content of OMVs does not fit a
stochastic model of content selection, revealing the significant retention of lipid
A species containing covalent modifications that mask their 1- and 4'-phosphate moieties
under host-like conditions. Furthermore, palmitoylation of the lipid A to form hepta-acylated
species substantially increases the likelihood of its incorporation into OMVs. These
results highlight a role for the OMV response in OM remodeling and maintenance processes
in Gram-negative bacteria.
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https://hdl.handle.net/10161/13027Published Version (Please cite this version)
10.1128/mBio.01532-16Publication Info
Bonnington, Katherine E; & Kuehn, Meta J (2016). Outer Membrane Vesicle Production Facilitates LPS Remodeling and Outer Membrane Maintenance
in Salmonella during Environmental Transitions. MBio, 7(5). 10.1128/mBio.01532-16. Retrieved from https://hdl.handle.net/10161/13027.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Margarethe Joanna Kuehn
Associate Professor of Biochemistry
Enterotoxigenic E. coli (ETEC) causes traveler's diarrhea and infant mortality in
underdeveloped countries, and Pseudomonas aeruginosa is an opportunistic pathogen
for immunocompromised patients. Like all gram negative bacteria studied to date, ETEC
and P. aeruginosa produce small outer membrane vesicles that can serve as delivery
"bombs" to host tissues. Vesicles contain a subset of outer membrane and
soluble periplasmic proteins and lipids. In tissues and sera of infected hosts,

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