Genomic structure of the Salmonella enterica serovar Typhimurium DT 64 bacteriophage ST64T: evidence for modular genetic architecture

Abstract

The complete sequence of the double-stranded DNA genome of a serotype-converting temperate bacteriophage, ST64T, was determined. The 40,679-bp genomic sequence of ST64T has an overall GC content of 47.5% and was reminiscent of a number of lambdoid phages, in particular, P22. Inferred proteins of ST64T which exhibited a high degree of sequence similarity to P22 proteins (>90%) included the functional serotype conversion cassette, integrase, excisionase, Abc1, Abc2, early antitermination (gp24), NinD, NinH, NinZ, packaging (gp3 and gp2), head (with the exception of gp26, gp7, gp20, and gp16), and tail proteins. The putative immunity genes were highly related to those of Salmonella enterica serotype Typhimurium phage L, whereas the lysis genes were almost identical to those of S. enterica serovar Typhimurium PS3.

FIG. 1.

Schematic representation of the phage ST64T genome indicating putative ORFs derived from the sequence. Similarities to other phage genes with known functions are indicated as shown below. The ORFs for which no genetic designation had been previously made are designated based upon the inferred size of the putative gene product: ▪, >90% similarity to phage P22; , <90% similarity to P22; ▤, similar to phage 21; □, no inferred function or similarity; , similar to phage L; ▥, similar to phage HK022; ▧, similar to phage PS3.

FIG. 2.

Hydropathy prediction of the putative Mnt protein of ST64T compared to the Mnt protein of P22 using the Kyte-Doolittle hydropathy algorithm (7). The plot was produced using the OMIGA 1.1 program. The black line represents Mnt_ST64T, and the dotted line represents Mnt_P22.