Specific Integration of Temperate Phage Decreases the Pathogenicity of Host Bacteria

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.

Bacteriophages as drivers of bacterial virulence and their potential for biotechnological exploitation

“…On the other hand, prophages have also shown to prevent the assembly of T4P on the bacterial surface 60 . In Bordetella bronchiseptica, the temperate bacteriophage PHB09 disrupts pili formation due to specific integration in the pilB gene of the host, leading to a reduced twitching motility and consequently a reduced overall virulence 61 .…”

“…For instance, the prophage 13 integrates within the hlb gene of S. aureus, leading to the loss of -toxin production by the pathogen 82 . Likewise, an attenuated virulence of B. bronchiseptica is observed by integration of phage PHB09 in its genome, due to disruption of the pilB gene 61 . Another sophisticated relationship that has been observed between a phage and pathogen in this context, is the phage-regulatory switch (phage-RS).…”

“…The most obvious application of this, would be the inhibition of virulence associated genes by phage integration, resulting in the disrupting of the bacterial encoded virulence factor. The previously mentioned S. aureus bacteriophage Sa3int and the B. bronchiseptica phage PBH09 could be applied to inactivate toxin B and PilB expression, respectively 61,84 . However, the stability of such an inactivation as well as the efficiency of phage infection and bacterial virulence reduction would need to be thoroughly assessed.…”

Identification and Functional Analysis of Temperate Siphoviridae Bacteriophages of Acinetobacter baumannii

“…Temperate phages are natural vectors for gene transmission among bacteria owing to their ability to integrate as prophages, and, consequently, affect the fitness and phenotype of the produced lysogen [25]. Several virulence factor or toxin encoding genes of pathogenic bacteria have been associated with prophages, indicating that temperate phages may play a significant role in increasing the host pathogenicity, on the other hand, a virulence-attenuating role is not often reported for temperate phages [26,27].…”

Characterization of a Lytic Bacteriophage vB_EfaS_PHB08 Harboring Endolysin Lys08 against Enterococcus faecalis Biofilms

“…The phages’ genomic DNA was extracted by using the phenol-chloroform protocol [ 39 ] and was then sequenced on an Illumina HiSeq 2,500 platform with a 2 × 100 bp read length. The short reads were assembled by SOAPdenovo [ 40 ].…”