In the current experiments, we used K-feldspar and Snomax as test INSs. Considering our use of OptiPrep™ (density of 1.320 g cm -3 ) as the density gradient medium, we expect K-feldspar, which has a density of 2.55 -2.63 g cm -3 , to pass through the density gradient medium and form a pellet. We assume Snomax has a buoyant density of approximately 1 -1.2 g cm -3 based on the density of bacterial cells. As a result, Snomax should not pass through the density gradient medium during density gradient centrifugation experiments.