Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>

ABSTRACT Biofilms are often described as protective shelters that preserve bacteria from hostile surroundings. However, biofilm bacteria are also exposed to various stresses and need to adjust to the heterogeneous physicochemical conditions prevailing within biofilms. In Gram-negative bacteria, such...

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Autores principales:	Magdalena Szczesny, Christophe Beloin, Jean-Marc Ghigo
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2018
Materias:	biofilm LPS Rcs envelope stress lipid A palmitoylation Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/8d80f37587464cf2b13f8d3e9b43fcee
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spelling	oai:doaj.org-article:8d80f37587464cf2b13f8d3e9b43fcee2021-11-15T16:00:15ZIncreased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>10.1128/mBio.01415-182150-7511https://doaj.org/article/8d80f37587464cf2b13f8d3e9b43fcee2018-09-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01415-18https://doaj.org/toc/2150-7511ABSTRACT Biofilms are often described as protective shelters that preserve bacteria from hostile surroundings. However, biofilm bacteria are also exposed to various stresses and need to adjust to the heterogeneous physicochemical conditions prevailing within biofilms. In Gram-negative bacteria, such adaptations can result in modifications of the lipopolysaccharide, a major component of the outer membrane characterized by a highly dynamic structure responding to environmental changes. We previously showed that Gram-negative biofilm bacteria undergo an increase in lipid A palmitoylation mediated by the PagP enzyme, contributing to increased resistance to host defenses. Here we describe a regulatory pathway leading to transcriptional induction of pagP in response to specific conditions created in the biofilm environment. We show that pagP expression is induced via the Rcs envelope stress system independently of the Rcs phosphorelay cascade and that it requires the GadE auxiliary regulator. Moreover, we identify an increase in osmolarity (i.e., ionic stress) as a signal able to induce pagP expression in an RcsB-dependent manner. Consistently, we show that the biofilm is a hyperosmolar environment and that RcsB-dependent pagP induction can be dampened in the presence of an osmoprotectant. These results provide new insights into the adaptive mechanisms of bacterial differentiation in biofilm. IMPORTANCE The development of the dense bacterial communities called biofilms creates a highly heterogeneous environment in which bacteria are subjected to a variety of physicochemical stresses. We investigated the mechanisms of a widespread and biofilm-associated chemical modification of the lipopolysaccharide (LPS), a major component of all Gram-negative bacterial outer membranes. This modification corresponds to the incorporation, mediated by the enzyme PagP, of a palmitate chain into lipid A (palmitoylation) that reduces bacterial recognition by host immune responses. Using biochemical and genetic approaches, we demonstrate that a significant part of biofilm-associated lipid A palmitoylation is triggered upon induction of pagP transcription by the hyperosmolar biofilm environment. pagP induction is regulated by RcsB, the response regulator of the Rcs stress response pathway, and is not observed under planktonic conditions. Our report provides new insights into how physiological adaptations to local biofilm microenvironments can contribute to decreases in susceptibility to antimicrobial agents and host immune defenses.Magdalena SzczesnyChristophe BeloinJean-Marc GhigoAmerican Society for MicrobiologyarticlebiofilmLPSRcs envelope stresslipid ApalmitoylationMicrobiologyQR1-502ENmBio, Vol 9, Iss 4 (2018)
institution	DOAJ
collection	DOAJ
language	EN
topic	biofilm LPS Rcs envelope stress lipid A palmitoylation Microbiology QR1-502
spellingShingle	biofilm LPS Rcs envelope stress lipid A palmitoylation Microbiology QR1-502 Magdalena Szczesny Christophe Beloin Jean-Marc Ghigo Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>
description	ABSTRACT Biofilms are often described as protective shelters that preserve bacteria from hostile surroundings. However, biofilm bacteria are also exposed to various stresses and need to adjust to the heterogeneous physicochemical conditions prevailing within biofilms. In Gram-negative bacteria, such adaptations can result in modifications of the lipopolysaccharide, a major component of the outer membrane characterized by a highly dynamic structure responding to environmental changes. We previously showed that Gram-negative biofilm bacteria undergo an increase in lipid A palmitoylation mediated by the PagP enzyme, contributing to increased resistance to host defenses. Here we describe a regulatory pathway leading to transcriptional induction of pagP in response to specific conditions created in the biofilm environment. We show that pagP expression is induced via the Rcs envelope stress system independently of the Rcs phosphorelay cascade and that it requires the GadE auxiliary regulator. Moreover, we identify an increase in osmolarity (i.e., ionic stress) as a signal able to induce pagP expression in an RcsB-dependent manner. Consistently, we show that the biofilm is a hyperosmolar environment and that RcsB-dependent pagP induction can be dampened in the presence of an osmoprotectant. These results provide new insights into the adaptive mechanisms of bacterial differentiation in biofilm. IMPORTANCE The development of the dense bacterial communities called biofilms creates a highly heterogeneous environment in which bacteria are subjected to a variety of physicochemical stresses. We investigated the mechanisms of a widespread and biofilm-associated chemical modification of the lipopolysaccharide (LPS), a major component of all Gram-negative bacterial outer membranes. This modification corresponds to the incorporation, mediated by the enzyme PagP, of a palmitate chain into lipid A (palmitoylation) that reduces bacterial recognition by host immune responses. Using biochemical and genetic approaches, we demonstrate that a significant part of biofilm-associated lipid A palmitoylation is triggered upon induction of pagP transcription by the hyperosmolar biofilm environment. pagP induction is regulated by RcsB, the response regulator of the Rcs stress response pathway, and is not observed under planktonic conditions. Our report provides new insights into how physiological adaptations to local biofilm microenvironments can contribute to decreases in susceptibility to antimicrobial agents and host immune defenses.
format	article
author	Magdalena Szczesny Christophe Beloin Jean-Marc Ghigo
author_facet	Magdalena Szczesny Christophe Beloin Jean-Marc Ghigo
author_sort	Magdalena Szczesny
title	Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>
title_short	Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>
title_full	Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>
title_fullStr	Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>
title_full_unstemmed	Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>
title_sort	increased osmolarity in biofilm triggers rcsb-dependent lipid a palmitoylation in <italic toggle="yes">escherichia coli</italic>
publisher	American Society for Microbiology
publishDate	2018
url	https://doaj.org/article/8d80f37587464cf2b13f8d3e9b43fcee
work_keys_str_mv	AT magdalenaszczesny increasedosmolarityinbiofilmtriggersrcsbdependentlipidapalmitoylationinitalictoggleyesescherichiacoliitalic AT christophebeloin increasedosmolarityinbiofilmtriggersrcsbdependentlipidapalmitoylationinitalictoggleyesescherichiacoliitalic AT jeanmarcghigo increasedosmolarityinbiofilmtriggersrcsbdependentlipidapalmitoylationinitalictoggleyesescherichiacoliitalic
_version_	1718426980575084544

Increased Osmolarity in Biofilm Triggers RcsB-Dependent Lipid A Palmitoylation in <italic toggle="yes">Escherichia coli</italic>

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