Suttle, C.A. and A.M. Chan. 1994. Dynamics and distribution of cyanophages and their effect on marine Synechococcus spp. Applied and Environmental Microbiology 60:3167-3174.

Cyanophages infecting marine Synechococcus were frequently very abundant and were found in every seawater sample along a transect in the western Gulf of Mexico, and during a 28 month period in Aransas Pass, Texas. In Aransas Pass their abundance varied seasonally with the lowest concentrations coincident with cooler water and lower salinity. Along the transect, viruses infecting Synechococcus strains DC2 and SYN48 ranged in concentration from a few hundred ml-1 at 97 m depth and 83 km offshore, to ca. 4 x 105 ml-1 near the surface at stations within 18 km of the coast. The highest concentrations occurred at the surface where salinity decreased from ca. 35.5 to 34 ppt and concentrations of Synechococcus were greatest. Viruses infecting strains SNC1, SNC2 and 838BG were distributed in a similar manner, but were much less abundant (< 10 to > 5 x 103 ml-1). When Synechococcus exceeded ca. 103 ml-1, cyanophage concentrations increased markedly (ca. 102 to > 105 ml-1), suggesting that there was a minimum host density required for efficient viral propagation. Data on the decay rate of viral infectivity (d; d-1) as a function of solar radiation (I; mmol quanta m-2 s-1) was used to develop a relationship (d = 0.2610 I - 0.00718; r2 = 0.69) for conservatively estimating the destruction of infectious viruses in the mixed layer of two offshore stations. Assuming that virus production balances losses, and burst size is 250, ca. 5-7 % of Synechococcus would be infected daily by viruses. Calculations based on contact rates between Synechococcus and infectious viruses produce similar results (5-14 %). Moreover, balancing estimates of viral production with contact rates for the most offshore station required that most Synechococcus be susceptible to infection, that most contacts result in infection and that the burst size be about 324 viruses per lytic event. In contrast, in nearshore waters where ca. 80 % of Synechococcus would be contacted daily by infectious cyanophages, only ca. 1 % of the contacts would have to result in infection, in order to balance the estimated virus removal rates. These results indicate that cyanophages are an abundant and dynamic component of marine planktonic communities and are likely responsible for lysing a small but significant portion of the Synechococcus population on a daily basis.

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