Degradation studies on Escherichia coli capsular polysaccharides by bacteriophages

Host range and influence of a cell capsule on the phage efficacy of three Lactococcus garvieae lytic phages

Three lytic phages (PLgW-1, PLgY-16, and PLgY-30) were previously used for phage-typing Lactococcus garvieae, a bacterial pathogen of various marine fish species, and were demonstrated to be potential therapeutants for infections caused by L. garvieae. The morphology, host range, and efficacy of these phages have not been investigated in detail, however. The current study examined the lysis spectrum of these 3 phages against 16 different genotypes of L. garvieae and the influence of a bacterial capsule on phage efficacy, to aid in developing an effective treatment for lactococcosis in fish. Morphological analysis by transmission electron microscopy revealed that all 3 phages belonged to the family Siphoviridae and had a minor difference in morphology. These phages lysed a high proportion of their bacterial host (93.7% of the different L. garvieae genotypes). In addition, the efficacy of the plating assays was affected by both the phages and their bacterial host, in which phage efficacy was clearly affected by a bacterial capsule. The results of this study may be useful for developing appropriate strategies to use these phages to control various genotypes of L. garvieae causing disease in marine fish.

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.