A current review (1) lists 21 cyanophages of coccoid and filamentous heterocystic and non-heterocystic blue-green algae (BGA). The capsid diameters of these viruses range from 50-90 nm, and none have been previously reported for Microcoleus,a sheath-producing, filamentous, surface colonizing BGA (Fig. 1), of the order Oscillatoriales, and class Cyanophyceae (= Cyanobacteria). From a freshwater culture of Microcoleussp. we report here a putative cyanophage with a side-to-side hexagonal capsid diameter of 140 nm, based on measurements from thin sections of algal filaments prepared for transmission electron microscopy (TEM).
An earlier report (2) documented the ultrastructure of mucilage secretion, and its role in sheath, trichome and filament formation in an isolate of the BGA Microcoleus sp. grown in soil-water medium. Now we report large cyanophage-like particles in a majority of cells making up the trichomes. These putative hexagonal viral capsids (Figs. 2-5) are mainly clustered in the center or to one side of the nucleoplasm.