This is a microscopy image of the bacteria from freshly fallen snow. The snow samples were collected on the terrasse of the High Altitude Research Station Jungfraujoch in Switzerland. The bacteria present in the snow were preserved with formaldehyde. The liquid sample was then passed through a filter, which retained the bacterial cells larger than 0.2 micrometers (which are most of the known bacteria). A fluorescent stain (DAPI) makes the bacterial cells visible under UV light and we can image them using a microscope.
With this method we can not only see that there is a large diversity of shapes of bacteria, but the number of cells present in 1 ml of melted snow can be estimated. In these samples, the bacterial cell counts average to around a million cells per ml! Isn’t that astounding considering that snow looks so super clean.