Snow Bugs: Growing a Culture from Filtered Snow

Vincent Giovannone

Introduction

This analysis is from Tin B filters of our dirty snowball experiments (un-seeded) described in "Dirty Snow" in the 01 February 2008 The Citizen Scientist.

Once filters were dried, they were placed under a microscope to see what kind of particles were on them that could not be observed with the naked eye. Several particles were seen on the three filters used. Drawing or photographs could be made of the particles in the hope of trying to identify them. Some of the particles had numerous features including different colors, while others did not. Some were plain black and featureless.

I wondered if anything I was seeing would grow in the right conditions in a culture medium.

Materials

•  Small saucepan

•  1/3 cup of water (distilled)

•  1 teaspoon unflavored gelatin

•  1 teaspoon sugar

•  3 Petri dishes (sterile)

I made the culture medium by boiling the distilled water and then adding gelatin and sugar. I stirred for approximately one minute until everything was dissolved. I then poured the solution into the Petri dishes to a depth of about 6 mm (0.25 inch). Lids were then placed on each Petri dish, and the dishes were allowed to cool for three or four hours at room temperature. The solution hardened into a gel.

Procedure

Most of the particles were centered at the middle of the circular filter, so this portion of the filter was pressed into the culture medium. Care must be taken when doing this, and it is important to remember that we don't want to destroy the culture medium. So press gently so that the particles are transferred from the filter to the culture medium without damage. (In some cases you can remove a particle and place it into the culture medium, but this was not one of those cases.) Once this was done each Petri dish with material and lid in place was weighed. They were than placed in a cool, dry, dark place and left to incubate.

Results

The experiment was begun on 24 August 2007. For the first couple of days nothing could be seen growing in any of the dishes. On day four, I began to see some white spots in two of the Petri dishes and a dark spot in one of them. The growth of the cultures was very slow, so I decided to take digital pictures of the samples every 30 days or so. I labeled the Petri dishes P-A, P-B and P-C, P standing for Petri. (See Figure 1).

The Petri dishes lost weight as the water content of the agar evaporated. P-A had a starting weight of 9.72 grams, and its final weight was 7.94 grams. The weight of P-B fell from 10.32 to 7.98 grams. And the weight of P-C fell from 11.04 to 8.14 grams.

The first set of pictures was taken on 24 September 2007. None were taken in October, because there was no major change. A final set was taken on 25 November 2007, and the samples were destroyed on 26 November.

Figure 1 : A test photograph (P-C) after two weeks.

Conclusion

I was surprised by the results, for I was sure nothing was going to grow, having seen nothing in the first week. However, as the weeks went by things began to slowly happen. I have no samples to compare these samples to, so I'm not sure what we are seeing. Some of the colonies appear to mold and others bacteria.

At the center of almost every snow crystal is a tiny mote of dust, which can be anything from volcanic ash to a particle from outer space. It is known that bacteria can also serve as condensation nuclei, and this project confirms that.