Suttle, C.A. and A.M. Chan. 1994. What is the impact of viruses on marine Synechococcus? EOS 75:167.

The concentration of cyanophages infecting marine Synechococcus spp. were enumerated in samples of seawater along a transect in the western Gulf of Mexico, and during a 28 month period in Aransas Pass, Texas. Infective cyanophages were frequently very abundant and were found in every seawater sample that was screened. The abundance of cyanophages in Aransas Pass varied on a seasonal basis with the lowest concentrations coincident with cooler water temperatures and lower salinities. Along the offshore transect, viruses infecting Synechococcus spp. strains DC 2 and SYN 48 were found to range in concentration from a few hundred infectious units ml-1 at 97 m and 83 km offshore, to > 2 x 105 ml-1 near the surface at stations within 18 km of the coast. The highest concentrations were found near the surface in a region where salinity decreased from ca. 35.5 to 34 ppt and where concentrations of Synechococcus spp. were greatest. Viruses infecting other strains of Synechococcus spp. (SNC1, SNC2 and 838BG) were distributed in a similar manner, but were much less abundant, ranging from <10 to >5 x 103 ml-1. Cyanophage concentrations increased markedly when Synechococcus spp. exceeded ca. 103 ml-1 suggesting that there was a threshold in host density required for efficient viral propagation. Conservative estimates based on balancing virus production rates with removal rates of infectious viruses from seawater suggest that at the two offshore stations 5-7 % of Synechococcus spp. in the mixed layer would be lysed daily by cyanophages; whereas, at the inshore stations the range for the water column was 0.8 to 5 %. Calculations based on the transport of viruses to potential host cells indicated that the percent of Synechococcus cells that would be contacted by infectious cyanophages on a daily basis increased from 5 to 83 % along the offshore to onshore transect. These data support the argument that a significant amount of the primary productivity of cyanobacteria is shunted into a "viral loop"; thereby, affecting nutrients and energy cycling in marine systems.

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