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Genetic and Functional Diversity of Pseudomonas aeruginosa Lipopolysaccharide.

Lam JS, Taylor VL, Islam ST, Hao Y, Kocíncová D - Front Microbiol (2011)

Bottom Line: Most P. aeruginosa strains produce two distinct forms of O-Ag, one a homopolymer of D-rhamnose that is a common polysaccharide antigen (CPA, formerly termed A band), and the other a heteropolymer of three to five distinct (and often unique dideoxy) sugars in its repeat units, known as O-specific antigen (OSA, formerly termed B band).Compositional differences in the O units among the OSA from different strains form the basis of the International Antigenic Typing Scheme for classification via serotyping of different strains of P. aeruginosa.The focus of this review is to provide state-of-the-art knowledge on the genetic and resultant functional diversity of LPS produced by P. aeruginosa.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.

ABSTRACT
Lipopolysccharide (LPS) is an integral component of the Pseudomonas aeruginosa cell envelope, occupying the outer leaflet of the outer membrane in this Gram-negative opportunistic pathogen. It is important for bacterium-host interactions and has been shown to be a major virulence factor for this organism. Structurally, P. aeruginosa LPS is composed of three domains, namely, lipid A, core oligosaccharide, and the distal O antigen (O-Ag). Most P. aeruginosa strains produce two distinct forms of O-Ag, one a homopolymer of D-rhamnose that is a common polysaccharide antigen (CPA, formerly termed A band), and the other a heteropolymer of three to five distinct (and often unique dideoxy) sugars in its repeat units, known as O-specific antigen (OSA, formerly termed B band). Compositional differences in the O units among the OSA from different strains form the basis of the International Antigenic Typing Scheme for classification via serotyping of different strains of P. aeruginosa. The focus of this review is to provide state-of-the-art knowledge on the genetic and resultant functional diversity of LPS produced by P. aeruginosa. The underlying factors contributing to this diversity will be thoroughly discussed and presented in the context of its contributions to host-pathogen interactions and the control/prevention of infection.

No MeSH data available.


Related in: MedlinePlus

Proposed CPA gene clusters of (A) P. aeruginosa PAO1, (B) PA14, (C) LESB58, (E) PA7, and (D) P. fluorescens pfO-1. The organism-specific identifier for numbered genes of unknown function is indicated in brackets beside each organism.
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Figure 3: Proposed CPA gene clusters of (A) P. aeruginosa PAO1, (B) PA14, (C) LESB58, (E) PA7, and (D) P. fluorescens pfO-1. The organism-specific identifier for numbered genes of unknown function is indicated in brackets beside each organism.

Mentions: Cell density-dependent gene regulation plays an integral role in cell-surface virulence factor expression, altering gene expression based on population size (Whiteley et al., 1999). As previously mentioned, most P. aeruginosa CF isolates from chronically infected patients are devoid of OSA and begin to favor the typical “rough” phenotype, i.e., producing LPS that lacks the full-length O antigen side chain, being non-motile and non-piliated (Hancock et al., 1983). Although previous studies have shown the genetic relationship of the alginate-based mucoid phenotype (Ma et al., 1998), the regulation of changes governing the transition from smooth to rough LPS is not well defined. The “mucus inducible gene” migA (described above) is a putative glycosyltransferase and was discovered when P. aeruginosa was grown in the presence of CF mucus (Wang et al., 1996). Expression of the migA gene was found to be a result of quorum sensing (Whiteley et al., 1999), dependent on the release of autoinducer molecules by P. aeruginosa into the local environment. When the bacterial density increases to an appropriate level, the local concentration of autoinducer molecules reaches a critical threshold past which they can consistently bind to transcription regulators across the entire cell population, resulting in alternative gene expression across the entire community (Fuqua et al., 1994). The migA gene was found to be under the control of RhlI–RhlR regulatory system, one of the two principal quorum-sensing systems, due to its severe decrease in expression in a rhlI–rhlR double knockout as compared to wildtype. Furthermore, it possesses an upstream las-box-like sequence (CT-N11)-AG), known to be a quorum-sensing recognition site for quorum-sensing regulators (Yang et al., 2000). Interestingly, overexpression of migA resulted in a loss of “core-plus-one” but not the higher molecular weight LPS, leading the authors to speculate the existence of a secondary glycosyltransferase (Yang et al., 2000). Recently that second glycosyltransferase was identified by our group as wapR, located 158-bp downstream of the core biosynthesis locus (Poon et al., 2008). Genetic and biophysical analysis of these two genes and their products revealed that both are responsible for core modifications in LPS biosynthesis (Figure 3). The expression of these genes results in an altered core structure: migA is responsible for the addition of the L-rhamnoseA (L-RhaA) in the α1 → 6 linkage, preventing the addition of O-Ag to lipid A-core by the O-Ag ligase WaaL (Yang et al., 2000; Poon et al., 2008). The wapR gene is responsible for the addition of the core sugar L-RhaB, creating the favored linkage site for the addition of the O-Ag by WaaL (Poon et al., 2008). A genomic knockout of wapR resulted in the loss of higher molecular weight LPS bands, corresponding with the addition of O-Ag to lipid A-core. Work is currently underway in our laboratory to establish the relationship between migA and wapR gene expression. The cell density-dependent effects on gene regulation are of particular importance as CF isolates are often found in mature biofilms, a direct byproduct of quorum sensing.


Genetic and Functional Diversity of Pseudomonas aeruginosa Lipopolysaccharide.

Lam JS, Taylor VL, Islam ST, Hao Y, Kocíncová D - Front Microbiol (2011)

Proposed CPA gene clusters of (A) P. aeruginosa PAO1, (B) PA14, (C) LESB58, (E) PA7, and (D) P. fluorescens pfO-1. The organism-specific identifier for numbered genes of unknown function is indicated in brackets beside each organism.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3108286&req=5

Figure 3: Proposed CPA gene clusters of (A) P. aeruginosa PAO1, (B) PA14, (C) LESB58, (E) PA7, and (D) P. fluorescens pfO-1. The organism-specific identifier for numbered genes of unknown function is indicated in brackets beside each organism.
Mentions: Cell density-dependent gene regulation plays an integral role in cell-surface virulence factor expression, altering gene expression based on population size (Whiteley et al., 1999). As previously mentioned, most P. aeruginosa CF isolates from chronically infected patients are devoid of OSA and begin to favor the typical “rough” phenotype, i.e., producing LPS that lacks the full-length O antigen side chain, being non-motile and non-piliated (Hancock et al., 1983). Although previous studies have shown the genetic relationship of the alginate-based mucoid phenotype (Ma et al., 1998), the regulation of changes governing the transition from smooth to rough LPS is not well defined. The “mucus inducible gene” migA (described above) is a putative glycosyltransferase and was discovered when P. aeruginosa was grown in the presence of CF mucus (Wang et al., 1996). Expression of the migA gene was found to be a result of quorum sensing (Whiteley et al., 1999), dependent on the release of autoinducer molecules by P. aeruginosa into the local environment. When the bacterial density increases to an appropriate level, the local concentration of autoinducer molecules reaches a critical threshold past which they can consistently bind to transcription regulators across the entire cell population, resulting in alternative gene expression across the entire community (Fuqua et al., 1994). The migA gene was found to be under the control of RhlI–RhlR regulatory system, one of the two principal quorum-sensing systems, due to its severe decrease in expression in a rhlI–rhlR double knockout as compared to wildtype. Furthermore, it possesses an upstream las-box-like sequence (CT-N11)-AG), known to be a quorum-sensing recognition site for quorum-sensing regulators (Yang et al., 2000). Interestingly, overexpression of migA resulted in a loss of “core-plus-one” but not the higher molecular weight LPS, leading the authors to speculate the existence of a secondary glycosyltransferase (Yang et al., 2000). Recently that second glycosyltransferase was identified by our group as wapR, located 158-bp downstream of the core biosynthesis locus (Poon et al., 2008). Genetic and biophysical analysis of these two genes and their products revealed that both are responsible for core modifications in LPS biosynthesis (Figure 3). The expression of these genes results in an altered core structure: migA is responsible for the addition of the L-rhamnoseA (L-RhaA) in the α1 → 6 linkage, preventing the addition of O-Ag to lipid A-core by the O-Ag ligase WaaL (Yang et al., 2000; Poon et al., 2008). The wapR gene is responsible for the addition of the core sugar L-RhaB, creating the favored linkage site for the addition of the O-Ag by WaaL (Poon et al., 2008). A genomic knockout of wapR resulted in the loss of higher molecular weight LPS bands, corresponding with the addition of O-Ag to lipid A-core. Work is currently underway in our laboratory to establish the relationship between migA and wapR gene expression. The cell density-dependent effects on gene regulation are of particular importance as CF isolates are often found in mature biofilms, a direct byproduct of quorum sensing.

Bottom Line: Most P. aeruginosa strains produce two distinct forms of O-Ag, one a homopolymer of D-rhamnose that is a common polysaccharide antigen (CPA, formerly termed A band), and the other a heteropolymer of three to five distinct (and often unique dideoxy) sugars in its repeat units, known as O-specific antigen (OSA, formerly termed B band).Compositional differences in the O units among the OSA from different strains form the basis of the International Antigenic Typing Scheme for classification via serotyping of different strains of P. aeruginosa.The focus of this review is to provide state-of-the-art knowledge on the genetic and resultant functional diversity of LPS produced by P. aeruginosa.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.

ABSTRACT
Lipopolysccharide (LPS) is an integral component of the Pseudomonas aeruginosa cell envelope, occupying the outer leaflet of the outer membrane in this Gram-negative opportunistic pathogen. It is important for bacterium-host interactions and has been shown to be a major virulence factor for this organism. Structurally, P. aeruginosa LPS is composed of three domains, namely, lipid A, core oligosaccharide, and the distal O antigen (O-Ag). Most P. aeruginosa strains produce two distinct forms of O-Ag, one a homopolymer of D-rhamnose that is a common polysaccharide antigen (CPA, formerly termed A band), and the other a heteropolymer of three to five distinct (and often unique dideoxy) sugars in its repeat units, known as O-specific antigen (OSA, formerly termed B band). Compositional differences in the O units among the OSA from different strains form the basis of the International Antigenic Typing Scheme for classification via serotyping of different strains of P. aeruginosa. The focus of this review is to provide state-of-the-art knowledge on the genetic and resultant functional diversity of LPS produced by P. aeruginosa. The underlying factors contributing to this diversity will be thoroughly discussed and presented in the context of its contributions to host-pathogen interactions and the control/prevention of infection.

No MeSH data available.


Related in: MedlinePlus