The Holin-Endolysin Lysis System of the OP2-Like Phage X2 Infecting Xanthomonas oryzae pv. oryzae.

Zhifeng Wu,Jianping Chen,Bin Li,Chenqi Yan,Yong Yang,Xinyang Xu,Belinda Loh,Yang Zhang,Sebastian Leptihn,Temoor Ahmed

doi:10.3390/v13101949

Abstract

Most endolysins of dsDNA phages are exported by a holin-dependent mechanism, while in some cases endolysins are exported via a holin-independent mechanism. However, it is still unclear whether the same endolysins can be exported by both holin-dependent and holin-independent mechanisms. This study investigated the lysis system of OP2-like phage X2 infecting Xanthomonas oryzae pv. oryzae, causing devastating bacterial leaf blight disease in rice. Based on bioinformatics and protein biochemistry methods, we show that phage X2 employs the classic "holin-endolysin" lysis system. The endolysin acts on the cell envelope and exhibits antibacterial effects in vitro, while the holin facilitates the release of the protein into the periplasm. We also characterized the role of the transmembrane domain (TMD) in the translocation of the endolysin across the inner membrane. We found that the TMD facilitated the translocation of the endolysin via the Sec secretion system. The holin increases the efficiency of protein release, leading to faster and more efficient lysis. Interestingly, in E. coli, the expression of either holin or endolysin with TMDs resulted in the formation of long rod shaped cells. We conclude that the TMD of X2-Lys plays a dual role: One is the transmembrane transport while the other is the inhibition of cell division, resulting in larger cells and thus in a higher number of released viruses per cell.

Highlights

Phages are viruses that infect bacteria [1]
This study identified and systematically analyzed the holin-endolysin lysis system of the OP2-like phage X2, which has the ability to infect and inactivate the most important bacterial rice pathogen
In silico analysis revealed that the endolysin of OP2-like phages lack a transmembrane domain (TMD), suggesting X2-Lys alone is unable to achieve bacterial lysis and requires the type II holin X2-Hol, which exhibits substantial differences compared to the holin found in Xanthomonas oryzae pv. oryzae (Xoo) OP1-like phages

Summary

Introduction

Phages (or bacteriophages) are viruses that infect bacteria [1]. Most doublestranded DNA (dsDNA) tailed phages (i.e., Caudovirales) make use of the canonical holinendolysin system to release progeny virions during the final stages of the lytic life cycle, resulting in lysis and killing the host. Food and agriculture is being extensively explored as an alternative to chemical treatments, which addresses concerns regarding safety, environmental burden and antimicrobial resistance of antibiotic substances. Alternatives such as the use of bacteriophages or their proteins as bacterial biocontrol agents has attracted much attention in recent years [6,7,8,9,10]. As a potential biological control agent in various food processing environments, the endolysin of a Staphylococcus aureus phage has been shown to effectively remove Staphylococcus biofilms on the surface of food [12]

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Conclusion