Abstract
Temperate phages are considered as natural vectors for gene transmission among bacteria due to the ability to integrate their genomes into a host chromosome, therefore, affect the fitness and phenotype of host bacteria. Many virulence genes of pathogenic bacteria were identified in temperate phage genomes, supporting the concept that temperate phages play important roles in increasing the bacterial pathogenicity through delivery of the virulence genes. However, little is known about the roles of temperate phages in attenuation of bacterial virulence. Here, we report a novel Bordetella bronchiseptica temperate phage, vB_BbrS_PHB09 (PHB09), which has a 42,129-bp dsDNA genome with a G+C content of 62.8%. Phylogenetic analysis based on large terminase subunit indicated that phage PHB09 represented a new member of the family Siphoviridae. The genome of PHB09 contains genes encoding lysogen-associated proteins, including integrase and cI protein. The integration site of PHB09 is specifically located within a pilin gene of B. bronchiseptica. Importantly, we found that the integration of phage PHB09 significantly decreased the virulence of parental strain B. bronchiseptica Bb01 in mice, most likely through disruption the expression of pilin gene. Moreover, a single shot of the prophage bearing B. bronchiseptica strain completely protected mice against lethal challenge with wild-type virulent B. bronchiseptica, indicating the vaccine potential of lysogenized strain. Our findings not only indicate the complicated roles of temperate phages in bacterial virulence other than simple delivery of virulent genes but also provide a potential strategy for developing bacterial vaccines.
Highlights
IntroductionBacteriophages (or phages), which infect bacteria, are the most abundant organisms on the earth
Bacteriophages, which infect bacteria, are the most abundant organisms on the earth
The phage PHB09 genome was sequenced, and the large terminase subunit (ORF31) was used to generate phylogenetic trees, which indicated that PHB09 is a new member of the family Siphoviridae (Figure 1)
Summary
Bacteriophages (or phages), which infect bacteria, are the most abundant organisms on the earth. Many studies have indicated that the infection of temperate phages might lead to the enhancement of host virulence as many virulent genes of pathogenic bacteria were identified in the phage genome (Boyd, 2012). Many effector proteins, which are bacterial virulent factors and are injected into host cells by bacterial type III secretion system to help bacterial invasion and survival, were identified in Salmonella typhimurium phages (Figueroa-Bossi et al, 2001). Infection with such temperate phages might lead to the transmission of the virulent genes, increases the virulence of host bacteria (Cuenca Mdel et al, 2016). In contrast to the enhancement of virulence, the roles of temperate phages in attenuation of bacterial virulence are largely unknown
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