Osmoregulated Periplasmic Glucans of Erwinia chrysanthemi

Abstract

OPGs were isolated by trichloracetic acid treatment and gel permeation chromatography. The synthesis of these compounds appeared to be osmoregulated, since lower amounts of OPGs were produced when bacteria were grown in media of higher osmolarities. However, a large fraction of these OPGs were recovered in the culture medium. Then, these compounds were characterized by compositional analysis, high-performance anion-exchange chromatography, matrix-assisted laser desorption mass spectrometry, and 1 H and 13 C nuclear magnetic resonance analyses. OPGs produced by E. chrysanthemi are very heterogeneous at the level of both backbone structure and substitution of these structures. The degree of polymerization of the glucose units ranges from 5 to 12. The structures are branched, with a linear backbone consisting of ␤-1,2-linked glucose units to which a variable number of branches, composed of one glucose residue, are attached by ␤-1,6 linkages in a random way. This glucan backbone may be substituted by O-acetyl and O-succinyl ester-linked residues.Osmoregulated periplasmic glucans (OPGs) are general constituents of the envelopes of gram-negative bacteria (4). Glucose is the sole constitutive sugar, and their abundance in the periplasmic compartment is osmoregulated, with the highest levels synthesized during growth at very low osmolarity. Four families of OPGs have been described on the basis of structural features of the polyglucose backbone. In family I, OPGs appear to range from 5 to 12 glucose residues, with the principal species containing 8 or 9 glucose residues. The structure is highly branched, the backbone consisting of ␤-1,2-linked glucose units to which the branches are attached by ␤-1,6 linkages. In family II, OPGs are composed of a cyclic ␤-1,2-glucan backbone containing 17 to 25 glucose residues. In family III, OPGs are ␤-1,6 and ␤-1,3 cyclic glucans containing 10 to 13 glucose units per ring. In family IV, OPGs are cyclic and have a unique degree of polymerization (DP, ϭ 13, 16, or 18). One linkage is ␣-1,6 whereas all the other glucose residues are linked by ␤-1,2 linkages. Depending on the species considered, OPGs can be modified to various extents by a variety of substituents. Mutations at the loci ndvA and ndvB in Sinorhizobium meliloti (8), ndvB and ndvC in Bradyrhizobium japonicum (3), chvA and chvB in Agrobacterium tumefaciens (17), and hrpM in Pseudomonas syringae (11, 13) impair OPG biosynthesis, and these mutants fail to interact properly with a host plant as a symbiont or a pathogen. However, beyond this functional homology, the OPGs synthesized by these different bacteria are very different in structure. The OPGs of S. meliloti and A. tumefaciens are cyclic structures of family II that may be modified with anionic substituents such as phosphoglycerol and/or succinyl moieties (5), the OPGs of B. japonicum are cyclic structures of family III that may be modified by substitution with phosphocholine (18), while the OPGs of P. syringae are linear and highly branched and devoid of any substituents...

Osmoregulated Periplasmic Glucan Synthesis Is Required for Erwinia chrysanthemi Pathogenicity

“…These results indicate that OPGs are necessary not only for plant colonization, but also for bacterial multiplication in macerated tissues. When E. chrysanthemi is grown in a liquid medium, a large fraction of the OPGs produced can be recovered in the medium, at least under certain circumstances (9). We have no indication whether this is true when bacteria grow in planta.…”

“…In E. coli, the mdoC gene, involved in OPG succinylation, is located just upstream from the mdoGH operon (21). Despite the fact that the OPGs of E. chrysanthemi are succinylated (9), no gene homologous to mdoC was found upstream of the opgGH operon. The 13-bp direct repeats found upstream from opgGH could be the limit of a chromosomal rearrangement mediated by a transposable element.…”

“…In Escherichia coli, the backbone, containing 7 to 13 glucose units, is substituted with phosphoglycerol, phosphoethanolamine, and succinyl residues (19). In Erwinia chrysanthemi, the backbone contains 5 to 12 glucose units substituted with succinyl and acetyl residues (9), and in Pseudomonas syringae, the backbone, consisting of 6 to 13 glucose units, is not substituted (38). In E. coli, the OPG backbone is synthesized by the products of the mdoGH operon located in the vicinity of pyrC, a gene involved in the biosynthesis of uracil (6).…”

Osmoregulated periplasmic glucans of Salmonella enterica serovar Typhimurium are required for optimal virulence in mice

“…have emerged from the present study. For example, opgGH mutants of Erwinia chrysanthemi showed increased capsular polysaccharide synthesis (giving rise to mucoid colonies) as well as hypersensitivity towards bile salts (Cogez et al, 2001;Page et al, 2001). No change in colony morphology or change in sensitivity towards bile salts was observed for strain SG111 (Fig S1a).…”

The Brucella abortus Cyclic β-1,2-Glucan Virulence Factor Is Substituted with O-Ester-Linked Succinyl Residues

“…Cyclic glucans of Azospirillum brasilense (1) are substituted only with succinyl residues, and cyclic glucans of B. japonicum are substituted only with phosphocholine (35). Cyclic glucan from S. meliloti and Agrobacterium tumefaciens are substituted with both succinyl and phosphoglycerol residues (7), while the cyclic glucan of Rhodobacter sphaeroides (41) and linear glucans of Erwinia chrysanthemi (15) are substituted with succinyl and acetate residues. Osmoregulated periplasmic glucans (OPG) originating from Escherichia coli (linear glucans) are the only ones known to be substituted with three different substituents, phosphoglycerol, phosphoethanolamine, and succinyl residues (27).…”