This high-magnification microscopic image shows yellow-stained bacteria, each one about 1 micrometer wide, colonizing sediment grains from the deep sea. Such images allow us to determine the number of bacteria in sediments (this sample has already been diluted 10,000-fold), but not which ones are active, since any intact cell containing DNA, whether it is active or dormant, will take up this stain. Image courtesy of Arctic Exploration 2002, Shelly Carpenter, NOAA/OER.
