Isolation and genome analysis of a new freshwater Microcystis cyanophage vB_MweS-yong2

Abstract:

[Objective] Cyanobacterial blooms break out frequently and cause water quality deterioration.Cyanobacterial toxins (cyanotoxins) have hepatotoxicity,neurotoxicity,reproductive and genetic toxicity and tumor promoting effects,threatening the drinking water safety.Cyanobacterial blooms contribute to toxin accumulation or death of aquatic organisms,risking edible safety of aquatic products and causing huge economic losses to aquaculture industry.Cyanophages are viruses that specifically infect cyanobacteria and regulate its population density and abundance.They are considered as an important potential biological control tool for cyanobacterial blooms.Study on freshwater cyanophage is rarely reported,which is far less than that on seawater cyanophage.So far,little is known about Microcystis wesenbergii cyanophage.[Methods] In this study,we isolated a virulent freshwater cyanophage vB_MweS-yong2 by double-layer agar plate method using M.wesenbergii FACHB-1112 as the indicator host.Genome sequencing,open reading frame (ORF) annotation and phylogenetic analysis of cyanophage vB_MweS-yong2 were performed.[Results]vB_MweS-yong2 genome was a double-stranded DNA of 44 530 bp,with a G+C content of 71.6% and containing 61 ORFs and 1 tRNA gene.No vB_MweS-yong2 ORF was found to be associated with virulence factors and antibiotic resistance genes.The pairwise sequence comparison (PASC) scanning illustrated that the highest nucleotide sequence similarity between vB_MweS-yong2 and all known phages in databases was 20.21%,which was<50%(the boundary to define a genus).[Conclusion] vB_MweS-yong2 was proposed to represent a new genus in the Siphoviridae family of Caudovirales order.These works enriched the freshwater cyanophage database and laid a foundation for the research and development of the functional genes of cyanophages and the control of cyanobacterial blooms with M.wesenbergii as the dominant species.

Key words:Microcystins wesenbergii;cyanophage;genome;phylogenetic analysis