Novel Freshwater Cyanophages Provide New Insights into Evolutionary Relationships between Freshwater and Marine Cyanophages.

Dong Zhang,Karina Yew-Hoong Gin,Yiliang He,Erik F Y Hom

doi:10.1128/spectrum.00593-21

Abstract

ABSTRACTCyanobacteria and cyanophages are present widely in both freshwater and marine environments. However, freshwater cyanophages remain unknown largely due to the small numbers of cyanophage isolates despite their ecological and environmental significance. In this study, we present the characterization of two novel lytic freshwater cyanophages isolated from a tropical inland lake in Singapore, namely, cyanopodovirus S-SRP01 and cyanomyovirus S-SRM01, infecting two different strains of Synechococcus spp. Functional annotation of S-SRP01 and S-SRM01 genomes revealed a high degree of homology with marine cyanophages. Phylogenetic trees of concatenated genes and whole-genome alignment provided further evidence that S-SRP01 is close evolutionarily to marine cyanopodoviruses, while S-SRM01 is evolutionarily close to marine cyanomyoviruses. Few genetic similarities between freshwater and marine cyanophages have been identified in previous studies. The isolation of S-SRP01 and S-SRM01 expand current knowledge on freshwater cyanophages infecting Synechococcus spp. Their high degree of gene sharing provides new insights into the evolutionary relationships between freshwater and marine cyanophages. This relatedness is further supported by the discovery of similar phenomenon from other freshwater viral metagenomes.IMPORTANCE This study expands the current knowledge on freshwater cyanophage isolates and cyanophage genetic diversity, indicating that freshwater and marine cyanophages infecting Synechococcus spp. may share close genetic similarity and evolutionary relationships.

Highlights

Cyanobacteria and cyanophages are present widely in both freshwater and marine environments
The purified S-SRM01 particle has a polyhedral shape with head diameter of approximately 85 nm (Fig. 1A)
Transmission electron microscopy (TEM) of purified S-SRP01 particle revealed its icosahedral shape with a diameter of approximately 50 nm (Fig. 1B)

Summary

Introduction

Cyanobacteria and cyanophages are present widely in both freshwater and marine environments. Little genomic similarity has been found to be shared among freshwater and marine cyanophage isolates with the exception of T4-like phage S-CRM01 [12, 23]. A total of 14 out of 15 marine cyanopodovirus core genes could be identified in the S-SRP01 genome with the exception of the tail fiber protein [10].

Results

Conclusion