Interactions between the Prophage 919TP and Its Vibrio cholerae Host: Implications of gmd Mutation for Phage Resistance, Cell Auto-Aggregation, and Motility

Na Li,Mathias Middelboe,Yigang Zeng,Sine Lo Svenningsen,Tongyu Zhu,Demeng Tan,Bijie Hu

doi:10.3390/v13122342

Abstract

Prophage 919TP is widely distributed among Vibrio cholera and is induced to produce free φ919TP phage particles. However, the interactions between prophage φ919TP, the induced phage particle, and its host remain unknown. In particular, phage resistance mechanisms and potential fitness trade-offs, resulting from phage resistance, are unresolved. In this study, we examined a prophage 919TP-deleted variant of V. cholerae and its interaction with a modified lytic variant of the induced prophage (φ919TP cI-). Specifically, the phage-resistant mutant was isolated by challenging a prophage-deleted variant with lytic phage φ919TP cI-. Further, the comparative genomic analysis of wild-type and φ919TP cI--resistant mutant predicted that phage φ919TP cI- selects for phage-resistant mutants harboring a mutation in key steps of lipopolysaccharide (LPS) O-antigen biosynthesis, causing a single-base-pair deletion in gene gmd. Our study showed that the gmd-mediated O-antigen defect can cause pleiotropic phenotypes, e.g., cell autoaggregation and reduced swarming motility, emphasizing the role of phage-driven diversification in V. cholerae. The developed approach assists in the identification of genetic determinants of host specificity and is used to explore the molecular mechanism underlying phage-host interactions. Our findings contribute to the understanding of prophage-facilitated horizontal gene transfer and emphasize the potential for developing new strategies to optimize the use of phages in bacterial pathogen control.

Highlights

Vibrio cholerae, the etiologic agent of the diarrheal disease cholera, is one of the most prevalent aquatic human pathogens and is responsible for disease and mortality in many countries [1]
Our study showed that the gmd-mediated O-antigen defect can cause pleiotropic phenotypes, e.g., cell autoaggregation and reduced swarming motility, emphasizing the role of phage-driven diversification in V. cholerae
In order to gain a better understanding of how spontaneous prophage activity drives the evolution of bacteria and the underlying molecular mechanisms, detailed knowledge of phage-host interaction is required

Summary

Introduction

The etiologic agent of the diarrheal disease cholera, is one of the most prevalent aquatic human pathogens and is responsible for disease and mortality in many countries [1]. Important virulence factors in V. cholerae, such as the cholera toxin (CTX) and Zonula occludens toxin (zot), are encoded by prophages [2], i.e., bacteriophage genomes that are integrated into the genome of the bacterial host or exist as an extrachromosomal plasmid. The interactions with bacteriophages are, important for the pathogenicity and dissemination of virulence in V. cholerae. The CTX and Zot toxins are carried by filamentous phages, which do not lyse their host cells upon propagation but are secreted through the host membrane in an infection process called a chronic cycle. Despite V. cholerae being a highly studied model bacterium and an important human pathogen, the role of several prophages and the corresponding free phage particles, such as phage φ919TP, remain to be experimentally characterized [3]. When CI repressor concentration is high, it represses the development of the lytic life cycle of the prophage [4]

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Conclusion