Marine cyanophages infecting oceanic and coastal strains of Synechococcus: abundance, . morphology, cross-infectivity and growth characteristics

Eight different phycoerythrinand phycocyanin-containing strains of Synechococcus spp. and 1 strain of Anacystis marina were screened against 29 natural virus communities taken from 3 locations in south Texas (USA) coastal waters, at different times of the year. In add~tion, 1 sample was screened from Peconic Bay, New York, USA. Cyanophages were detected in all samples, but the frequency with which they were detected and their abundance depended upon the strain of Synechococcus sp. that was screened. Viruses that infected red Synechococcus spp. strains (DC2, SYN 48) were particularly common and in some instances were in excess of 105 ml-l The abundances of cyanophages were weakly correlated with temperature (r2= 0.53 to 0.70), although they occurred at all of the temperatures (12 to 30.4 "C) and salinities (18 to 70 ppt) that were screened. The 7 cyanophages that were cloned belonged to the same 3 families of viruses that have been observed to infect freshwater cyanobacteria, namely the Siphoviridae (formerly Styloviridae), Myoviridae and Podoviridae. The cyanophage clones varied in host-specificity. For example, 1 clone infected a single Synechococcus sp. strain of 12 that were tested, whereas, another infected 4 of 9 strains tested. Growth characteristics of 1 of the virus clones was determined for a single host (BCCI). Photosynthesis in BCCI was not affected until near the onset of cell lysis and the virus burst cycle was complete ca 17 h post-infection. The burst size was approximately 250 infective particles. The high abundance of cyanophages in the natural environment provides further evidence that viruses are probably important regulators of phytoplankton dynamics in marine systems.