Prevalence of highly host‐specific cyanophages in the estuarine environment

Abstract

Cyanophages that infect coastal and oceanic Synechococcus have been studied extensively. However, no cyanophages infecting estuarine Synechococcus have been reported. In this study, seven cyanophages (three podoviruses, three siphoviruses and one myovirus) isolated from four estuarine Synechococcus strains were characterized in terms of their morphology, host range, growth and genetic features. All the podoviruses and siphoviruses were highly host specific. For the first time, the photosynthesis gene (psbA) was found in two podoviruses infecting estuarine Synechococcus. However, the psbA gene was not detected in the three siphoviruses. The psbA sequences from the two Synechococcus podoviruses clustered with some environmental psbA sequences, forming a unique cluster distantly related to previous known psbA clusters. Our results suggest that the psbA among Synechococcus podoviruses may evolve independently from the psbA of Synechococcus myoviruses. All three estuarine Synechococcus podoviruses contained the DNA polymerase (pol) gene, and clustered with other podoviruses that infect oceanic Synechococcus and Prochlorococcus, suggesting that the DNA pol is conserved among marine picocyanobacterial podoviruses. Prevalence of host-specific cyanophages in the estuary suggests that Synechococcus and their phages in the estuarine ecosystem may develop a host-phage relationship different from what have been found in the open ocean.

Ubiquitous cyanobacterial podoviruses in the global oceans unveiled through viral DNA polymerase gene sequences

“…P60 is a lytic phage that infects Synchococcus WH7805 (Chen and Lu, 2002), a cyanobacterium isolated from the Atlantic Ocean (Waterbury et al, 1986). P60 was recognized as a highly active phage because of its short latent period compared to other cyanophages (Wang and Chen, 2008). All the oceanic sequences in this subcluster shared greater than 97% amino-acid identity with P60, suggesting that P60-like podoviruses are common in the ocean and could be critical in regulating the population dynamics of oceanic cyanobacteria.…”

“…A recent study showed that podoviruses infecting marine picocyanobacteria contain a conserved DNA polymerase gene (DNA pol), which can be used as a gene marker to investigate the genetic diversity of these viruses (Wang and Chen, 2008). PCR amplification, cloning and sequencing of this viral DNA pol gene from field samples have uncovered new genotypes and subclusters of cyanopodoviruses in the Chesapeake Bay (Chen et al, 2009).…”

“…Typically, cyanomyoviruses are able to cross-infect a broad range of hosts, whereas cyanopodoviruses and cyanosiphoviruses are more host specific (Sullivan et al, 2003;Weigele et al, 2007;Wang and Chen, 2008). The genetic diversity of cyanomyoviruses in various aquatic environments has been explored extensively based on their conserved capsid gene (g20) (Fuller et al, 1998;Zhong et al, 2002;Wang and Chen, 2004;Filee et al, 2005;Short and Suttle, 2005;Wilhelm et al, 2006;Sullivan et al, 2008).…”

“…Nearly 20 years ago, Proctor and Fuhrman (1990) reported that 1-3% of the cyanobacteria from diverse marine locations contained mature viral particles. Since then, viruses have been isolated using different groups of marine and freshwater picocyanobacteria, including Synechococcus and Prochlorococcus strains (Suttle and Chan, 1993;Waterbury and Valois, 1993;Wilson et al, 1993;Suttle, 2000;Lu et al, 2001;Sullivan et al, 2003;Sullivan et al, 2005;Wilhelm et al, 2006;Pope et al, 2007;Wang and Chen, 2008). It has been estimated that cyanophages may be responsible for approximately 5-14% of cyanobacterial mortality on a daily basis (Suttle and Chan, 1994;Binder 1999).…”

Diversity of active marine picoeukaryotes in the Eastern Mediterranean Sea unveiled using photosystem-II psbA transcripts

“…Carbon biomass was calculated according to Verity et al (1992 Amplification of psbA genes PsbA gene fragments (B750 bp) were amplified by PCR from cDNA and genomic DNA using the degenerated PCR primers designed by Wang and Chen (2008) that target the conserved YPIWEA and HNFPLD regions. PCR was performed in a total volume of 25 ml containing 10 ng of template DNA/cDNA, 2.5 ml of 10 X OptiBuffer, 2 ml of dNTP, 1.3 ml of 50 mM MgCl 2 , 1 ml of 25 mM psbA-1F (TAYCCNATYTGGGAAGC), 1 ml of 25 mM psbA-2R (TCRAGDGGGAARTTRTG), and 1.2 U of BIO-X-ACT (Bioline, London, UK).…”