Everybody Is Always Talking About The Weather… Revisited

Lenticular clouds above the Big Island.
Credit: astroday.net

A recent paper in Science adds evidence to the notion that ice nuclei, the particles that lead to the formation of rain and snow, are mainly of biological origin. In fact, lots of the ice nuclei contain bacteria that have wafted aloft. The researchers found that fresh snow in various parts of the world, including Antarctica, contains DNA in particles that are sensitive to both lysozyme and heat. We expect that metagenomics of such samples will follow.

Where do these bacteria that fly through the air with the greatest of ease come from?

The best guess is that they are lifted from the leaves of plants. They may well include Pseudomonas syringae, the organism with the reputation for causing ice formation on plants at relatively high temperatures. This new work is part of a small but tenacious literature on the subject of bacterial participation in atmospheric phenomena. For an evolutionary viewpoint, see John Dennehy’s blog; for a description of the challenges of living in the clouds, complete with pertinent references, see a blog sponsored by The New York Times. (Not that we suffer from comment-envy, but we couldn't help but notice that the latter got 129 comments!)

We have long known that bacteria contribute to the climate of this planet (that is, to long range atmospheric changes). There have been good reasons to think that bacteria might also influence the weather (i.e., what the forecasters tell you about today and the rest of the week). With these recent data, such claims become even more credible.

Comments

Sequence diversity of 16S rRNA is a fine criterion; but if Martian diversity stopped diversifying one or two billion years ago when the planet got too cold, measurement of diversity gets a little tricky.

Anyway, we got some folks interested. What a great blog!

-- stan zahler

[Eric J. Johnson]

> And there isn't any way to tell which was the original donor, which the original recipient.

Actually, how about sequence diversity at 16S rDNA and other highly conserved loci? Occam would provide that if one planet has significantly more diversity, it is much more likely to be the donor.

That's assuming we are talking about a transfer of bacteria, rather than of some kind of putative precellular, pre-ribosomal life. On the face of it, it seems like the proposed precellular organisms or protoorganisms about which I've happened to overhear (such as populate the basic "RNA world" kind of scenario) might not necessarily transfer well.

[Eric J. Johnson]

Stan, I don't know any exobiology, so I can't really evaluate this paper at all:

http://users.tpg.com.au/users/tps-seti/transpermia.html

...but, it reviews an estimate of a mean of 150 kg of biologically "hospitable" Earthly rock reaching Mars each year, and vice versa. "Hospitable" meaning that:

" - The radius of ejected rock is between 0.67 and 1 metre (mainly to provide protection from radiation in deep space).
- The core temperature within the rock during ejection or re-entry did not exceed 100 C (two of the dozen or so Martian meteorites that have been found on Earth meet this criterion)
- The journey time between planets was 100,000 years or less"

[stan zahler]

Let's extend this conversation a bit. I've often thought that if meteorites can knock hunks of Martian rocks to Earth, then surely Terran meteorites must knock earth rocks and soil to Mars occasionally. So naturally life on Mars will have right-handed sugars and DNAs and left-handed amino acids. And there isn't any way to tell which was the original donor, which the original recipient.

[Nathan W]

I've always meant to leave a comment but have never fealt that I would be able to add to the content of your posts. I will leave this here in the hope that I can help cure your comment envy. I would comment another 128 times, but I fear that would defeat the purpose.

As for actual content. Sea-spray must introduce a lot of microbes into the atmosphere.