The freshwater cyanophage AS-1 is a myovirus capable of infecting

Synechococcus sp. strain PCC6301 (formerly Anacystis nidulans) and Synechococcus cedrorum (Safferman et al., 1972). Early studies showed that light influenced the adsorption of AS-1 to Synechococcus sp. PCC6301, with only 40% of the phage adsorbed to the cells in the dark, compared with 80% in the light (Cseke & Farkas, 1979). However, a 10-fold increase in the Na+ concentration in the medium counteracted the effect of darkness and restored the adsorption of AS-1 to the level obtained in the light (Cseke & Farkas, 1979). This observation has been explained as being due to light-induced charge neutralization www.selleckchem.com/products/PD-0332991.html at the cell surface or by light-induced

changes in the ionic composition at the cell surface (Cseke & Farkas, 1979). Light was found to strongly influence the infection of Synechococcus elongatus sp. PCC7942 Akt targets by AS-1, with phage progeny production being correlated with a diel pattern under natural light (Kao et al., 2005). One effect of the light was at the level of adsorption. In this paper, the influence of light on adsorption was investigated using a model system consisting of the ‘photosynthetic’ cyanophage S-PM2 and its host the marine cyanobacterium Synechococcus sp. WH7803. Synechococcus sp. WH7803 and BL161 were grown in an artificial seawater (ASW) medium as described previously (Wilson et al., 1996). The cyanophages used in this study are listed in Table 1 and were propagated as described by Wilson et al. (1993). Phage titration was based on a previously reported protocol, with minor modifications (Wilson et al., 1996). Briefly, cyanophage samples were serially Calpain 10-fold diluted in ASW, and

samples were left to adsorb to 100-fold concentrated exponentially growing (OD750 nm of 0.35–0.40) Synechococcus sp. WH7803 cells for 1.5 h at 25 °C with gentle occasional shaking. The agar used in this study was cleaned using water, ethanol and acetone according to a well-established method (Waterbury & Willey, 1988). These phage–cell suspensions were then evenly mixed with 3 mL 0.3% w/v molten ASW agar and poured as top layers onto 1% w/v ASW agar plates before being kept on the bench at room temperature for at least 2 h. These plates were incubated in a Sanyo Environmental Test Chamber (model: MLR-351H) at 25 °C with illumination at 15–25 μE m−2 s−1. Plaques, which normally appeared within 7 days, were counted manually. Control plates received ASW with no cyanophage. To determine the kinetics of adsorption under light and dark conditions, cyanophage S-PM2 was added to two identical samples of cells from cultures of Synechococcus sp. WH7803 (OD750 nm of 0.35–0.40) at a multiplicity of infection (MOI) of 0.02. The MOI was determined by dividing the number of phages added by the number of bacteria added.