Cesium Chloride Gradients
Prepare cesium chloride densities of p1.2, p1.4, p1.5 and p1.65 in seawater (sw) that has been 0.02μm (or 0.2μm) filtered and autoclaved.
Place tube of prepared cesium on balance.  
Tare balance to 0. 
Remove 1ml with sterile pipet tip.
Layer CsCl from the bottom using a gradient fractionator if you have one or by hand. 
Carefully layer on sample (~5ml can be layered with SW40 ~15ml with SW28).
Weigh and balance tubes.
Centrifuge using SW40 or SW28 Beckman rotor @ 24,000rpm for 4hr at 4°C. 
Have sterile 0.5ml tubes (SW40) or 1.5ml tubes (SW28) labeled 1-24 Open tubes in a rack.
Place tube on ring stand. 
Puncture about 2mm from the bottom side of the tube using a sterile 20 guage needle, bevel up.
Collect droplets to fill each tube in order.
Place tube with sample on 4-place balance in holder.
Tare to 0.
With sterile pipet tip, remove 100µl.
Take measurement.
Return sample to tube.
Remove another 100µl, take measurement, return sample to tube.
Remove yet another 100µl, take measurement, and return sample to tube.
After all tubes have been measured, take average of the 3 values for each tube.
Multiply by 10.
Pool and extract DNA or can confirm presence of virus first by staining 10µl with SYBR gold. 
Count under fluorescent scope.
Pool all samples with virus.
