The structure of the O-specific polysaccharide from the lipopolysaccharide of Aeromonas bestiarum strain 207

Immunochemical studies and gene cluster relationships of closely related O-antigens of Aeromonas hydrophila Pt679, Aeromonas popoffii A4, and Aeromonas sobria K928 strains classified into the PGO1 serogroup dominant in Polish aquaculture of carp and rainbow trout

The present study included three Aeromonas sp. strains isolated from fish tissues during Motile Aeromonas Infection/Motile Aeromonas Septicaemia disease outbreaks on commercial farms, i.e.: Aeromonas hydrophila Pt679 obtained from rainbow trout as well as Aeromonas popoffii A4 (formerly Aeromonas encheleia) and Aeromonas sobria K928 both isolated from carp, which were classified into the new provisional PGO1 serogroup prevailing among aeromonads in Polish aquaculture. The structure of the O-specific polysaccharides of A4 and K928 has been previously established. Here, immunochemical studies of the O-specific polysaccharide of A. hydrophila Pt679 were undertaken. The O-specific polysaccharide was obtained from the lipopolysaccharide of A. hydrophila Pt679 after mild acid hydrolysis and separation by gel-permeation chromatography. The high-molecular-mass fraction was studied using chemical methods and ¹H and ¹³C NMR spectroscopy, including ¹H,¹H NOESY, and ¹H,¹³C HMBC experiments. The following structure of the branched repeating unit of the O-polysaccharide from A. hydrophila Pt679 was determined: [Formula: see text] The studies indicated that O-polysaccharides from A. hydrophila Pt679, A. popoffii A4 and A. sobria K928 share similarities but they also contain unique characteristics. Western blotting and an enzyme-linked immunosorbent assay revealed that the cross-reactivity of the related O-antigens is caused by the occurrence of common structural elements, whereas additional epitopes define the specificity of the O-serotypes. For genetic relationship studies, the O-antigen gene cluster was characterized in the genome of the A. hydrophila Pt679 strain and compared with the corresponding sequences of A. popoffii A4 and A. sobria K928 and with sequences available in the databases. The composition of the regions was found to be consistent with the O-antigen structures of Aeromonas strains classified into the same PGO1 serogroup.

Structure and gene cluster annotation of the O-antigen of Aeromonas sobria strain K928 isolated from common carp and classified into the new Aeromonas PGO1 serogroup

Aeromonas sobria strain K928 was isolated from a common carp during a Motile Aeromonas Infection/Motile Aeromonas Septicaemia disease outbreak on a Polish fish farm and classified into the new provisional PGO1 serogroup. The lipopolysaccharide of A. sobria K928 was subjected to mild acid hydrolysis, and the O-specific polysaccharide, which was isolated by gel-permeation chromatography, was studied using sugar and methylation analyses and ¹H and ¹³C NMR spectroscopy. The following structure of the branched O-specific polysaccharide repeating unit of A. sobria K928 was established. →2)[α-D-Fucp3NRHb-(1→3)]-α-L-Rhap-(1→3)-β-L-Rhap-(1→4)-α-L-Rhap-(1→3)-β-D-FucpNAc-(1→ The O-antigen gene cluster was identified and characterized in the genome of the A. sobria K928 strain after comparison with sequences in the available databases. The composition of the O-antigen genetic region was found to be consistent with the O-polysaccharide structure, and its organization was proposed.

Structure of the lipopolysaccharide O-antigen of Aeromonas encheleia strain A4 representing the new PGO1 serogroup of aeromonads prevailing in Polish aquaculture

The structure of the O-specific polysaccharide (OPS) from Aeromonas encheleia strain A4 lipopolysaccharide was investigated. A. encheleia strain A4, classified into the new provisional serogroup PGO1 predominating among aeromonads in Polish aquaculture, was isolated from common carp tissues during an outbreak of MAI/MAS disease on a fish farm. The high-molecular-weight OPS fraction liberated from the lipopolysaccharide after mild acid hydrolysis followed by gel-permeation chromatography was studied with chemical methods, mass spectrometry, and one- and two-dimensional ¹H and ¹³C NMR spectroscopy techniques. Inter-residue correlations were identified in ¹H,¹³C-heteronuclear multiple-bond correlation (HMBC) and ¹H,¹H NOESY experiments. It was found that the O-specific polysaccharide of A. encheleia strain A4 consists of branched pentasaccharide repeating units with the following structure:→2)[α-d-Fucp3NRHb-(1→3)]-α-l-Rhap-(1→3)-β-l-Rhap-(1→4)-α-l-Rhap-(1→3)-β-d-QuipNAc-(1→.

Synthesis of the Aeromonas veronii strain Bs8 disaccharide repeating unit

Presented herein is the synthesis of the Aeromonas veronii disaccharide repeating unit which has been achieved in 11 steps starting from d-fucose and d-galactosamine.

Complete Characterization of the O-Antigen from the LPS of Aeromonas bivalvium

Aeromonas species are found in the aquatic environment, drinking water, bottled mineral water, and different types of foods, such as meat, fish, seafood, or vegetables. Some of these species are primary or opportunistic pathogens for invertebrates and vertebrates, including humans. Among the pathogenic factors associated with these species, there are the lipopolysaccharides (LPSs). LPSs are the major components of the external leaflet of Gram-negative bacterial outer membrane. LPS is a glycoconjugate, generally composed of three portions: lipid A, core oligosaccharide, and O-specific polysaccharide or O-antigen. The latter, which may be present (smooth LPS) or not (rough LPS), is the most exposed part of the LPS and is involved in the pathogenicity by protecting infecting bacteria from serum complement killing and phagocytosis. The O-antigen is a polymer of repeating oligosaccharide units with high structural variability, particularly the terminal sugar, that confers the immunological specificity to the O-antigen. In this study, we established the structure of the O-chain repeating unit of the LPS from Aeromonas bivalvium strain 868 E^T (=CECT 7113^T = LMG 23376^T), a mesophilic bacterium isolated from cockles (Cardium sp.) and obtained from a retail market in Barcelona (Spain), whose biosynthesis core LPS cluster does not contain the waaE gene as most of Aeromonas species. After mild acid hydrolysis, the lipid A was removed by centrifugation and the obtained polysaccharide was fully characterized by chemical analysis and NMR spectroscopy. The polymer consists of a heptasaccharide repeating unit containing D-GalNAc, L-Rha, D-GlcNAc, and D-FucNAc residues.

A Unique Sugar l-Perosamine (4-Amino-4,6-dideoxy-l-mannose) Is a Compound Building Two O-Chain Polysaccharides in the Lipopolysaccharide of Aeromonas hydrophila Strain JCM 3968, Serogroup O6

Lipopolysaccharide (LPS) is the major glycolipid and virulence factor of Gram-negative bacteria, including Aeromonas spp. The O-specific polysaccharide (O-PS, O-chain, O-antigen), i.e., the surface-exposed part of LPS, which is a hetero- or homopolysaccharide, determines the serospecificity of bacterial strains. Here, chemical analyses, mass spectrometry, and ¹H and ¹³C NMR spectroscopy techniques were employed to study the O-PS of Aeromonas hydrophila strain JCM 3968, serogroup O6. MALDI-TOF mass spectrometry revealed that the LPS of A. hydrophila JCM 3968 has a hexaacylated lipid A with conserved architecture of the backbone and a core oligosaccharide composed of Hep₆Hex₁HexN₁HexNAc₁Kdo₁P₁. To liberate the O-antigen, LPS was subjected to mild acid hydrolysis followed by gel-permeation-chromatography and revealed two O-polysaccharides that were found to contain a unique sugar 4-amino-4,6-dideoxy-l-mannose (N-acetyl-l-perosamine, l-Rhap4NAc), which may further determine the specificity of the serogroup. The first O-polysaccharide (O-PS1) was built up of trisaccharide repeating units composed of one α-d-GalpNAc and two α-l-Rhap4NAc residues, whereas the other one, O-PS2, is an α1→2 linked homopolymer of l-Rhap4NAc. The following structures of the O-polysaccharides were established: O-PS1

→3)-α-l-Rhap4NAc-(1→4)-α-d-GalpNAc-(1→3)-α-l-Rhap4NAc-(1→

O-PS2

→2)-α-l-Rhap4NAc-(1→

The present paper is the first work that reveals the occurrence of perosamine in the l-configuration as a component of bacterial O-chain polysaccharides.

Synthesis of the repeating unit of O-specific polysaccharide isolated from the water-borne bacteria Aeromonas bestiarum 207

Aeromonas bestiarum 207 is a bacterial pathogen with severe impact on aquaculture. In a recent study, the structure of OPS antigens from Aeromonas bestiarum was identified as pentasaccharide repeating units. Synthesis of the pentasaccharide repeating unit and its derivative are reported. Stereo- and regio-specific synthesis was achieved under Schmidt glycosylation conditions employing appropriately protected L-rhamopyranosyl and D-glucopyranosylamine building blocks. The pentasaccharide synthesis was achieved using a [3 + 2] strategy with an overall yield of 5.2% through 11 linear steps from the monosaccharide building blocks 10 and 14.

Microbial Diversity of Source and Point-of-Use Water in Rural Haiti - A Pyrosequencing-Based Metagenomic Survey

Haiti endures the poorest water and sanitation infrastructure in the Western Hemisphere, where waterborne diseases cause significant morbidity and mortality. Most of these diseases are reported to be caused by waterborne pathogens. In this study, we examined the overall bacterial diversity of selected source and point-of-use water from rural areas in Central Plateau, Haiti using pyrosequencing of 16s rRNA genes. Taxonomic composition of water samples revealed an abundance of Firmicutes phyla, followed by Proteobacteria and Bacteroidetes. A total of 38 bacterial families and 60 genera were identified. The presence of several Klebsiella spp. (tentatively, K. pneumoniae, K. variicola and other Klebsiella spp.) was detected in most water samples. Several other human pathogens such as Aeromonas, Bacillus, Clostridium, and Yersinia constituted significantly higher proportion of bacterial communities in the point-of-use water samples compared to source water. Bacterial genera traditionally associated with biofilm formation, such as Chryseobacterium, Fusobacterium, Prevotella, Pseudomonas were found in the point-of-use waters obtained from water filters or domestic water storage containers. Although the pyrosequencing method utilized in this study did not reveal the viability status of these pathogens, the abundance of genetic footprints of the pathogens in water samples indicate the probable risk of bacterial transmission to humans. Therefore, the importance of appropriate handling, purification, and treatment of the source water needed to be clearly communicated to the communities in rural Haiti to ensure the water is safe for their daily use and intake.

Impact of stress on Aeromonas diversity in tambaqui (Colossoma macropomum) and lectin level change towards a bacterial challenge

Tambaqui (Colossoma macropomum) is among the most cultivated fish species in tropical countries. Stress is the main cause of disease in fish farms. The genus Aeromonas is a common causative agent of fish diseases. This work reports the identification of Aeromonas species colonizing gills of C. macropomum submitted or not to a confinement stress. We also evaluated changes in serum levels of lectins (carbohydrate-binding proteins that are components of fish immune system) in tambaqui submitted to a challenge using two isolated Aeromonas strains. Gill tissues from stressed and unstressed fishes were used to isolate Aeromonas. Then 72 Aeromonas strains were isolated, 97% being from stressed fishes. Among these, 63 were identified at species level and 6 were classified as atypical Aeromonas strains. The most prevalent species were Aeromonas bestiarum and Aeromonas caviae and their strains were used in bacterial challenges. The lectin serum levels significantly increased after 24 h of infection with A. bestiarum; however, no significant increase was found for infection with A. caviae. In conclusion, C. macropomum gills are susceptible to colonization by different Aeromonas species, mainly at confinement stressful conditions, and serum lectins may have a role in the acute immunological response towards infection by A. bestiarum.

Flexibility at a glycosidic linkage revealed by molecular dynamics, stochastic modeling, and (13)C NMR spin relaxation: conformational preferences of α-L-Rhap-α-(1 → 2)-α-L-Rhap-OMe in water and dimethyl sulfoxide solutions

The monosaccharide L-rhamnose is common in bacterial polysaccharides and the disaccharide α-L-Rhap-α-(1 → 2)-α-L-Rhap-OMe represents a structural model for a part of Shigella flexneri O-antigen polysaccharides. Utilization of [1'-(13)C]-site-specific labeling in the anomeric position at the glycosidic linkage between the two sugar residues facilitated the determination of transglycosidic NMR (3)JCH and (3)JCC coupling constants. Based on these spin-spin couplings the major state and the conformational distribution could be determined with respect to the ψ torsion angle, which changed between water and dimethyl sulfoxide (DMSO) as solvents, a finding mirrored by molecular dynamics (MD) simulations with explicit solvent molecules. The (13)C NMR spin relaxation parameters T1, T2, and heteronuclear NOE of the probe were measured for the disaccharide in DMSO-d6 at two magnetic field strengths, with standard deviations ≤1%. The combination of MD simulation and a stochastic description based on the diffusive chain model resulted in excellent agreement between calculated and experimentally observed (13)C relaxation parameters, with an average error of <2%. The coupling between the global reorientation of the molecule and the local motion of the spin probe is deemed essential if reproduction of NMR relaxation parameters should succeed, since decoupling of the two modes of motion results in significantly worse agreement. Calculation of (13)C relaxation parameters based on the correlation functions obtained directly from the MD simulation of the solute molecule in DMSO as solvent showed satisfactory agreement with errors on the order of 10% or less.

Structure of the O-specific polysaccharide from the lipopolysaccharide of Aeromonas sobria strain Pt312

The O-specific polysaccharide (OPS) obtained by mild-acid degradation of the lipopolysaccharide from Aeromonas sobria strain Pt312 was studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including 2D 1H,1H COSY, TOCSY, NOESY, 1H-detected 1H,13C HSQC, and HMBC experiments. The sequence of the sugar residues was determined using 1H,1H NOESY and 1H,13C HMBC experiments. It was found that the OPS was built up of disaccharide repeating units composed of GlcpNAc and non-stoichiometrically O-acetylated Rhap residues, and had the structure.

Structural studies of the lipopolysaccharide from the fish pathogen Aeromonas veronii strain Bs19, serotype O16

Chemical analyses, mass spectrometry, and NMR spectroscopy were applied to study the structure of the lipopolysaccharide (LPS) isolated from Aeromonas veronii strain Bs19, serotype O16. ESI-MS revealed that the most abundant LPS glycoforms have tetra-acylated or hexa-acylated lipid A species, consisting of a bisphosphorylated GlcN disaccharide with an AraN residue as a non-stoichiometric substituent, and a core oligosaccharide composed of Hep₅Hex₃HexN₁Kdo₁P₁. Sugar and methylation analysis together with 1D and 2D ¹H and ¹³C NMR spectroscopy were the main methods used, and revealed that the O-specific polysaccharide (OPS) of A. veronii Bs19 was built up of tetrasaccharide repeating units with the structure: →4)-α-d-Quip3NAc-(1→3)-α-l-Rhap-(1→4)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→. This composition was confirmed by mass spectrometry. The charge-deconvoluted ESI FT-ICR MS recorded for the LPS preparations identified mass peaks of SR- and R-form LPS species, that differed by Δm = 698.27 u, a value corresponding to the calculated molecular mass of one OPS repeating unit (6dHexNAc6dHexHexHexNAc-H₂O). Moreover, unspecific fragmentation spectra confirmed the sequence of the sugar residues in the OPS and allowed to assume that the elucidated structure also represented the biological repeating unit.

Structural and immunochemical studies of the lipopolysaccharide from the fish pathogen, Aeromonas bestiarum strain K296, serotype O18

Chemical analyses and mass spectrometry were used to study the structure of the lipopolysaccharide (LPS) isolated from Aeromonas bestiarum strain K296, serotype O18. ESI-MS revealed that the most abundant A. bestiarum LPS glycoforms have a hexa-acylated or tetra-acylated lipid A with conserved architecture of the backbone, consisting of a 1,4′-bisphosphorylated β-(1→6)-linked d-GlcN disaccharide with an AraN residue as a non-stoichiometric substituent and a core oligosaccharide composed of Kdo₁Hep₆Hex₁HexN₁P₁. 1D and 2D NMR spectroscopy revealed that the O-specific polysaccharide (OPS) of A. bestiarum K296 consists of a branched tetrasaccharide repeating unit containing two 6-deoxy-l-talose (6dTalp), one Manp and one GalpNAc residues; thus, it is similar to that of the OPS of A. hydrophila AH-3 (serotype O34) in both the sugar composition and the glycosylation pattern. Moreover, 3-substituted 6dTalp was 2-O-acetylated and additional O-acetyl groups were identified at O-2 and O-4 (or O-3) positions of the terminal 6dTalp. Western blots with polyclonal rabbit sera showed that serotypes O18 and O34 share some epitopes in the LPS. The very weak reaction of the anti-O34 serum with the O-deacylated LPS of A. bestiarum K296 might have been due to the different O-acetylation pattern of the terminal 6dTalp. The latter suggestion was further confirmed by NMR.

Aeromonas spp. whole genomes and virulence factors implicated in fish disease

It is widely recognized that Aeromonas infections produce septicaemia, and ulcerative and haemorrhagic diseases in fish, causing significant mortality in both wild and farmed freshwater and marine fish species that damage the economics of the aquaculture sector. The descriptions of the complete genomes of Aeromonas species have allowed the identification of an important number of virulence genes that affect the pathogenic potential of these bacteria. This review will focus on the most relevant information derived from the available Aeromonas genomes in relation to virulence and on the diverse virulence factors that actively participate in host adherence, colonization and infection, including structural components, extracellular factors, secretion systems, iron acquisition and quorum sensing mechanisms.

Structural analysis of the O-specific polysaccharide from the lipopolysaccharide of Aeromonas veronii bv. sobria strain K49

The O-specific polysaccharide obtained by mild-acid degradation of the lipopolysaccharide from Aeromonas veronii bv. sobria strain K49 was studied by sugar and methylation analyses along with (1)H and (13)C NMR spectroscopy. The sequence of the sugar residues was determined using (1)H,(1)H NOESY and (1)H,(13)C HMBC experiments. The O-specific polysaccharide was found to be a high molecular mass polysaccharide composed of repeating units of the structure: →2)-β-D-Quip3NAc-(1→3)-α-L-Rhap-(1→3)-α-L-Rhap-(1→2)-α-L-Rhap-(1→3)-α-D-FucpNAc-(1→ ESI MS confirmed the pentasaccharide structure of the repeating unit, as the molecular mass peaks seen in the spectrum differed by 812.34 u, a value corresponding to the calculated molecular mass of the O-unit.

The structural diversity of carbohydrate antigens of selected gram-negative marine bacteria

Marine microorganisms have evolved for millions of years to survive in the environments characterized by one or more extreme physical or chemical parameters, e.g., high pressure, low temperature or high salinity. Marine bacteria have the ability to produce a range of biologically active molecules, such as antibiotics, toxins and antitoxins, antitumor and antimicrobial agents, and as a result, they have been a topic of research interest for many years. Among these biologically active molecules, the carbohydrate antigens, lipopolysaccharides (LPSs, O-antigens) found in cell walls of gram-negative marine bacteria, show great potential as candidates in the development of drugs to prevent septic shock due to their low virulence. The structural diversity of LPSs is thought to be a reflection of the ability for these bacteria to adapt to an array of habitats, protecting the cell from being compromised by exposure to harsh environmental stress factors. Over the last few years, the variety of structures of core oligosaccharides and O-specific polysaccharides from LPSs of marine microrganisms has been discovered. In this review, we discuss the most recently encountered structures that have been identified from bacteria belonging to the genera Aeromonas, Alteromonas, Idiomarina, Microbulbifer, Pseudoalteromonas, Plesiomonas and Shewanella of the Gammaproteobacteria phylum; Sulfitobacter and Loktanella of the Alphaproteobactera phylum and to the genera Arenibacter, Cellulophaga, Chryseobacterium, Flavobacterium, Flexibacter of the Cytophaga-Flavobacterium-Bacteroides phylum. Particular attention is paid to the particular chemical features of the LPSs, such as the monosaccharide type, non-sugar substituents and phosphate groups, together with some of the typifying traits of LPSs obtained from marine bacteria. A possible correlation is then made between such features and the environmental adaptations undertaken by marine bacteria.

Structural characterization of the O-specific polysaccharide from the lipopolysaccharide of the fish pathogen Aeromonas bestiarum strain P1S

The O-specific polysaccharide obtained by mild-acid degradation of lipopolysaccharide of Aeromonas bestiarum P1S was studied by sugar and methylation analyses along with (1)H and (13)C NMR spectroscopy. The sequence of the sugar residues was determined using (1)H,(1)H NOESY and (1)H,(13)C HMBC experiments. The O-specific polysaccharide was found to be a high-molecular-mass polysaccharide composed of tetrasaccharide repeating units of the structure [formula in text]. Since small amounts of a terminal Quip3N residue were identified in methylation analysis, it was assumed that the elucidated structure also represented the biological repeating unit of the O-specific polysaccharide.