A bacteriophage-associated glycanase cleaving beta-pyranosidic linkages of 3-deoxy-D-manno-2-octulosonic acid (KDO)

The marine bacteria Cobetia marina DSMZ 4741 synthesizes an unexpected K-antigen-like exopolysaccharide

We have studied the exopolysaccharide produced by Cobetia marina DSMZ 4741, a marine bacterium isolated from coastal seawater. This strain is able to produce a polysaccharide in presence of carbon sources as glucose, mannitol and alginate. The maximum production occurs in aerobic condition, during the end of the exponential phase. The polymer is a non-viscous, acidic heteropolysaccharide of 270kDa constituted of a repeating unit of: This kind of chemical structure is generally related to K-antigen polysaccharide of pathogenic Escherichia coli strains. This is the first time this type of EPS is described from a marine bacterium. Moreover the polysaccharide exhibits a pyruvate substitution on its 3-deoxy-d-manno-oct-2-ulosonic acid (KDO) residue never encountered before. The discovery of such an unexpected EPS with high biotechnological potential is a new incentive for a better exploration of bioactive marine resources.

Escherichia coli K1's capsule is a barrier to bacteriophage T7

Escherichia coli strains that produce the K1 polysaccharide capsule have long been associated with pathogenesis. This capsule is believed to increase the cell's invasiveness, allowing the bacteria to avoid phagocytosis and inactivation by complement. It is also recognized as a receptor by some phages, such as K1F and K1-5, which have virion-associated enzymes that degrade the polysaccharide. In this report we show that expression of the K1 capsule in E. coli physically blocks infection by T7, a phage that recognizes lipopolysaccharide as the primary receptor. Enzymatic removal of the K1 antigen from the cell allows T7 to adsorb and replicate. This observation suggests that the capsule plays an important role as a defense against some phages that recognize structures beneath it and that the K1-specific phages evolved to counter this physical barrier.

Genomic Analysis of Bacteriophages SP6 and K1-5, an Estranged Subgroup of the T7 Supergroup

We have determined the genome sequences of two closely related lytic bacteriophages, SP6 and K1-5, which infect Salmonella typhimurium LT2 and Escherichia coli serotypes K1 and K5, respectively. The genome organization of these phages is almost identical with the notable exception of the tail fiber genes that confer the different host specificities. The two phages have diverged extensively at the nucleotide level but they are still more closely related to each other than either is to any other phage currently characterized. The SP6 and K1-5 genomes contain, respectively, 43,769 bp and 44,385 bp, with 174 bp and 234 bp direct terminal repeats. About half of the 105 putative open reading frames in the two genomes combined show no significant similarity to database proteins with a known or predicted function that is obviously beneficial for growth of a bacteriophage. The overall genome organization of SP6 and K1-5 is comparable to that of the T7 group of phages, although the specific order of genes coding for DNA metabolism functions has not been conserved. Low levels of nucleotide similarity between genomes in the T7 and SP6 groups suggest that they diverged a long time ago but, on the basis of this conservation of genome organization, they are expected to have retained similar developmental strategies.

Genome organization and characterization of mycobacteriophage Bxb1

Mycobacteriophage Bxb1 is a temperate phage of Mycobacterium smegmatis. The morphology of Bxb1 particles is similar to that of mycobacteriophages L5 and D29, although Bxb1 differs from these phages in other respects. First, it is heteroimmune with L5 and efficiently forms plaques on an L5 lysogen. Secondly, it has a different host range and fails to infect slow-growing mycobacteria, using a receptor system that is apparently different from that of L5 and D29. Thirdly, it is the first mycobacteriophage to be described that forms a large prominent halo around plaques on a lawn of M. smegmatis. The sequence of the Bxb1 genome shows that it possesses a similar overall organization to the genomes of L5 and D29 and shares weak but detectable DNA sequence similarity to these phages within the structural genes. However, Bxb1 uses a different system of integration and excision, a repressor with different specificity to that of L5 and encodes a large number of novel gene products including several with enzymatic functions that could degrade or modify the mycobacterial cell wall.

Degradation studies on Escherichia coli capsular polysaccharides by bacteriophages

The serologically and structurally related Eschrichia coli capsular polysaccharides (K antigens) K13, K20, and K23 were found to be depolymerized by the bacteriophages phi K13 and phi K20 to almost similar oligomer profiles as shown by polyacrylamide gel electrophoresis. The phage-polysaccharide interactions were followed by an increase of reducing 2-keto-3-deoxyoctulosonic acid due to a phage-associated glycanase that catalyzed the hydrolytic cleavage of common beta-ketopyranosidic 2-keto-3-deoxyoctulosonic acid linkages. The related E. coli K antigens K18, K22, and K100 as well as the Haemophilus influenzae type b capsular polysaccharide were degraded by bacteriophage phi K100 with different efficacy. It is suggested that phi K100 enzymatically cleaves ribitol-5-phosphate bonds as the only structural feature present in all the polysaccharides investigated.

Detection of Escherichia coli K95 strains by bacteriophages

A set of three bacteriophages (phi K5, phi K20, and phi K95) was used to discriminate between Escherichia coli K5 and K95 strains isolated from patients with urinary tract infections. All the strains tested were detected primarily by phi K5 and thought to carry the capsular antigen K5. Ten O2, 33 O6, and 32 O18 strains proved to be sensitive to the three phages. Eleven of 44 O75:H- strains, all 8 O75:H5 strains, 1 O17 strain, and 1 OR strain were not lysed by phage phi K20, the only phage without activity toward the K95 test strain. It has been suggested that the phi K20-resistant strains carry K95. These findings were confirmed by countercurrent immunoelectrophoresis with K-antigen extracts and anti-K95 serum. These preliminary data indicate the usefulness of these phages to detect K95 strains among K5 isolates.

Isolation and characterization of bacteriophages specific for capsular antigens K3, K7, K12, and K13 of Escherichia coli

Four bacteriophages recognizing the Escherichia coli capsular antigens K3, K7, K12, and K13, respectively, were isolated from pooled sewage samples. The nucleic acid of these phages was identified as double-stranded DNA of different size (phi K3, 71.3; phi K7, 32.8; phi K12, 42.9; phi K13, 43.4 kbp). Three of these phages belonged to Bradley's morphology group C and were specific for K3, K7, and K12 antigens, respectively. The phage phi K13 (Bradley's group A) attacked not only E. coli K13 strains but also E. coli producing the closely related K20 and K23 antigens. It is suggested that the common basic repeating units occurring in these capsular polysaccharides are the primary receptor of phi K13. It could be demonstrated that the four phages were able to depolymerize enzymatically the capsular polysaccharides isolated from the respective host strains.

Bacteriophage-associated glycan hydrolases specific for Escherichia coli capsular serotype K12

Four bacteriophages were identified, which carry glycan hydrolases specific for the Escherichia coli K12 capsular polysaccharide. All these glycanases catalyze the hydrolysis of the alpha-L-rhamnosyl-1,5-beta-3-deoxy-D-manno-2-octulosonic acid linkage as demonstrated with a special thiobarbituric acid assay procedure, which discriminates between the C5 substituted and unsubstituted 3-deoxy-D-manno-2-octulosonic acid (dOclA). This assay, together with gel filtration, 1H-NMR and 13C-NMR spectroscopy showed that depolymerization led to the dimer of the K12 repeating unit, (,5-beta-dOcl1Ap-2,3-alpha-LRhap-1,2-alpha LRhap-1,)2, as the primary degradation product. The phages (phi 12-W, phi 12-S, phi 82-W1, phi 82-W2) were tested for their ability to infect Escherichia coli strains Su65-42 (O4:K12:H-) and CDC63-57 [O139:K82(12):H1]. phi 12-W and phi 12-S, respectively, infected strain Su65-42 only, phi 82-W2 CDC63-57 only, and phi 82-W1 both bacterial strains. These distinct host specificities cannot be explained by differences in the action of the glycanases, which depolymerize the capsules of both strains.

Two additional bacteriophage-associated glycan hydrolases cleaving ketosidic bonds of 3-deoxy-D-manno-octulosonic acid in capsular polysaccharides of Escherichia coli

Two bacteriophages degrading 3-deoxy-D-manno-2-octulosonic acid-(KDO)-containing capsules of Escherichia coli strains were identified. Using modifications of the thiobarbituric acid assay, it was shown that each phage contains a glycan hydrolase activity cleaving one type of ketosidic linkage of KDO. Thus, the enzyme from phage phi 95 catalyzes the hydrolysis of beta-octulofuranosidonic linkages of the K95 glycan; and phi 1092, the alpha-octulopyranosidonic linkages of the K? antigen of E. coli LP1092. No cross-reactivity of the phage enzymes with other KDO-containing capsular polysaccharides was observed.