Mesophilic Aeromonas UDP-glucose pyrophosphorylase (GalU) mutants show two types of lipopolysaccharide structures and reduced virulence

Abstract

A mutation in galU that causes the lack of O34-antigen lipopolysaccharide (LPS) in Aeromonas hydrophila strain AH-3 was identified. It was proved that A. hydrophila GalU is a UDP-glucose pyrophosphorylase responsible for synthesis of UDP-glucose from glucose 1-phosphate and UTP. The galU mutant from this strain showed two types of LPS structures, represented by two bands on LPS gels. The first one (slow-migrating band in gels) corresponds to a rough strain having the complete core, with two significant differences: it lacks the terminal galactose residue from the LPS-core and 4-amino-4-deoxyarabinose residues from phosphate groups in lipid A. The second one (fast-migrating band in gels) corresponds to a deeply truncated structure with the LPS-core restricted to one 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) and three L-glycero-Dmanno-heptose residues. galU mutants in several motile mesophilic Aeromonas strains from serotypes O1, O2, O11, O18, O21 and O44 were also devoid of the O-antigen LPS. The galU mutation reduced to less than 1 % the survival of these Aeromonas strains in serum, decreased the ability of these strains to adhere and reduced by 1.5 or 2 log units the virulence of Aeromonas serotype O34 strains in a septicaemia model in either fish or mice. All the changes observed in the galU mutants were rescued by the introduction of the corresponding single wild-type gene.

A Transposon Site Hybridization Screen IdentifiesgalUandwecBCas Important for Survival of Yersinia pestis in Murine Macrophages

“…Therefore, the effects of the galU mutant are likely pleiotropic, resulting in both truncated LOS core and lack of lipid A modification by aminoarabinose. Similar pleiotropic effects of galU inactivation have been reported previously for Aeromonas hydrophila (62).…”

“…In Aeromonas hydrophila, inactivation of galU results in lack of addition of aminoarabinose to lipid A as well as defects in biosynthesis of O antigen or core of LPS (62). To investigate the role of galU in addition of aminoarabinose to Y. pestis lipid A, the structure of lipid A isolated from the KIM6ϩ galU mutant growing at 26°C or 37°C was analyzed using MALDI-TOF mass spectrometry and compared with that of the parental KIM6ϩ strain.…”

Characterization of UDP-Glucose Dehydrogenase and UDP-Glucose Pyrophosphorylase Mutants ofProteus mirabilis: Defectiveness in Polymyxin B Resistance, Swarming, and Virulence

“…In Salmonella enterica and E. coli, both ugd and galU have been shown to be involved in the production of 4-aminoarabinose (16,20,21,48), which is necessary for modifying LPS to become more positively charged. Mutation in either ugd or galU can lead to an alteration in LPS structure in Salmonella, E. coli, Burkholderia, Aeromonas, and Vibrio (9,21,22,45,57). Here we also found that the ugd and galU mutants of P. mirabilis had altered LPS profiles and cell surface topologies ( Fig.…”

“…UDP-glucose is the precursor for synthesis of different surface structures, LPS, and extracellular polysaccharides (EPS). In many Gram-negative pathogens, mutation in galU leads to attenuated virulence, mainly because of changes in LPS or capsular structures (16,45,57). UDP-glucose dehydrogenase (Ugd) is an enzyme that converts UDP-glucose into UDP-glucuronic acid (10).…”

Requirement of the galU Gene for Polysaccharide Production by and Pathogenicity and Growth In Planta of Xanthomonas citri subsp. citri

“…UDP-glucose is involved in synthesis of glucosylated surface structures as a substrate for glucosyltransferase, and it is a glycosyl donor in the enzymatic biosynthesis of carbohydrates (9,46). Mutations in the galU gene have led to reduced virulence of a number of bacterial pathogens, including Escherichia coli (21,28), Klebsiella pneumoniae (7), Shigella flexneri (43), Actinobacillus pleuropneumoniae (38), Vibrio cholerae (34), Pseudomonas aeruginosa (37), and Mesophilic aeromonas (49). The reduced virulence of galU mutants has been associated mainly with changes in lipopolysaccharides (LPS), capsu-lar polysaccharides (CPS), or exopolysaccharides (EPS).…”