A Shigella boydii bacteriophage which resembles Salmonella phage ViI

Abstract

Background: Lytic bacteriophages have been applied successfully to control the growth of various foodborne pathogens. Sequencing of their genomes is considered as an important preliminary step to ensure their safety prior to food applications.

Results: The lytic bacteriophage, ΦSboM-AG3, targets the important foodborne pathogen, Shigella. It is morphologically similar to phage ViI of Salmonella enterica serovar Typhi and a series of phages of Acinetobacter calcoaceticus and Rhizobium meliloti. The complete genome of ΦSboM-AG3 was determined to be 158 kb and was terminally redundant and circularly permuted. Two hundred and sixteen open reading frames (ORFs) were identified and annotated, most of which displayed homology to proteins of Salmonella phage ViI. The genome also included four genes specifying tRNAs.

Conclusions: This is the first time that a Vi-specific phage for Shigella has been described. There is no evidence for the presence of virulence and lysogeny-associated genes. In conclusion, the genome analysis of ΦSboM-AG3 indicates that this phage can be safely used for biocontrol purposes.

Figure 1

Electron micrograph of phage ΦSboM-AG3. The phage has been negatively stained with 2% potassium phosphotungstate. The bar indicates 100 nm.

Figure 2

One-step growth curve of phage ΦSboM-AG3. Shigella boydii C865 was used as the host and the incubation temperature was 30°C

Figure 3

Genetic and physical map of phage ΦSboM-AG3 as prepared by using CGView [50]. The outer lane represents genes in the plus strand; tRNA genes are indicated in red. The next lane illustrates genes on the minus strand. The lane with bluish-green boxes represents TBLASTX analysis against the nucleotide sequence of Salmonella phage ViI. The lane with black peaks and valleys indicate the GC content, while the innermost lane (green and violet) shows a GC skew analysis.

Figure 4

Denaturing SDS-PAGE gel examination of purified ΦSboM-AG3 particles. It gives 15 bands of molecular weights ranging from approximately 12 to 126 kDa. Six bands have been analyzed by mass spectrometry (labeled from A to F).