Evidence for the Intense Exchange of MazG in Marine Cyanophages by Horizontal Gene Transfer

Michael J Bryan,Nigel J Burroughs,Edward M Spence,Samantha J Bryan,Martha R J Clokie,Nicholas H Mann

doi:10.1371/journal.pone.0002048

Abstract

BackgroundS-PM2 is a phage capable of infecting strains of unicellular cyanobacteria belonging to the genus Synechococcus. S-PM2, like other myoviruses infecting marine cyanobacteria, encodes a number of bacterial-like genes. Amongst these genes is one encoding a MazG homologue that is hypothesized to be involved in the adaption of the infected host for production of progeny phage.Methodology/Principal FindingsThis study focuses on establishing the occurrence of mazG homologues in other cyanophages isolated from different oceanic locations. Degenerate PCR primers were designed using the mazG gene of S-PM2. The mazG gene was found to be widely distributed and highly conserved among Synechococcus myoviruses and podoviruses from diverse oceanic provinces.Conclusions/SignificanceThis study provides evidence of a globally connected cyanophage gene pool, the cyanophage mazG gene having a small effective population size indicative of rapid lateral gene transfer despite being present in a substantial fraction of cyanophage. The Prochlorococcus and Synechococcus phage mazG genes do not cluster with the host mazG gene, suggesting that their primary hosts are not the source of the mazG gene.

Highlights

Unicellular cyanobacteria of the genera Synechococcus and Prochlorococcus are abundant in the world’s oceans, whilst phages infecting these organisms are thought to determine host community structure and to divert the flow of fixed carbon within the microbial loop
Phage S-PM2 is a marine myovirus originally isolated from the English Channel that infects strains of marine Synechococcus [2,3]
Albeit not marine, ppGpp was demonstrated to accumulate under conditions of energy limitation [8] and nitrogen starvation [9], whereas phage infection interfered with this accumulation [10]

Summary

Introduction

Unicellular cyanobacteria of the genera Synechococcus and Prochlorococcus are abundant in the world’s oceans, whilst phages infecting these organisms are thought to determine host community structure and to divert the flow of fixed carbon within the microbial loop Phage S-PM2 is a marine myovirus originally isolated from the English Channel that infects strains of marine Synechococcus [2,3] It has a comparatively large genome (,196 Kb) whose sequence was published in 2005 [2], encoding 239 open reading frames (ORFs), 20 of which share similarities with genes in their Synechococcus host including key photosynthesis genes. It has been suggested that the phage-encoded MazG operates to reduce the ppGpp pool in infected Synechococcus cells [11]. S-PM2, like other myoviruses infecting marine cyanobacteria, encodes a number of bacterial-like genes Amongst these genes is one encoding a MazG homologue that is hypothesized to be involved in the adaption of the infected host for production of progeny phage

Methods

Results

Conclusion