Horizontal Gene Transfer

Eastern Emerald Elysia - a sea slug. Photo by Patrick Krug of the
Encyclopedia or Life

Everyone knows the usual story of evolution. An organism wishes to pass on its genes to the next generation must do so by surviving and reproducing in a dynamic environment. It must evade predation, avoid the pitfalls associated with weather, find enough food to make it to the next day and convince a partner (if the organism reproduces sexually) to mate in order to pass on those genes. If the genes are well-suited to the context in which it evolved, then the next generation will be given the necessary tools to continue the same struggle. If the genes are not well-suited for some reason, or the environment or competition is too harsh, then the survival of the organism becomes questionable. This story works because of a mechanism we will call Vertical Gene Transfer (VGT). This is where genes are passed from parent to offspring through reproduction.

So, in light of this scientific truth, it may be surprising to know that VGT isn't the only game in town. There is a thing in the world called Horizontal Gene Transfer (HGT). Certain organisms are capable, it seems, of exchanging genes in ways that DO NOT involve the standard sexual or asexual reproduction model. There are several different ways in which HGT can happen:

Thoughts on Life’s Diaspora

Here is a continuation of the discussion regarding Panspermia, which is the idea that life can move from one planetary body to another, in effect seeding a lifeless world. It is a claim that is passed off as science fiction conjecture, in some circles; as perhaps a claim not entirely worthy of scientific investigation. Others, both scientists and laypeople, helpfully counter that the idea of panspermia, as it concerns the origins of life on Earth, is just passing the problem from one place to another without answering the fundamental question, which is "How did life first arise?"

I disagree with the first point, and largely agree with the second. The search for life outside of the Earth IS a goal worthy of scientific investigation. Due to the very reasons that the origins of life are, thus far, inexplicable, so should we regard with seriousness the search for extraterrestrial life as part of the effort to understand the mystery of life's origins. We have no clear answers as to why life arose here on Earth. Even if we do find that mysterious genesis and it sheds some light on the process, we will probably not have a clear understanding of the events that transpired in life's first steps. That will be the case until we have a clear, unambiguous example of non-Earth life with which to compare us to.

Arsenic-DNA Bacteria Disputed

In 2010, the journal Science published a paper by NASA Astrobiologist Felisa Wolfe-Simon and her team, which describes a rare extremophile found in Lake Mono, California. This bacteria, labeled GFAJ-1, appeared to be able to switch out the life essential element phosphorus for that of the chemically similar, but poisonous element arsenic. The implication was that if life on Earth could be persuaded to take in and use arsenic, which is very poisonous, then the possibilities for extraterrestrial life can be broadened to include arsenic-using organisms. it was a finding that immediately caused a stir in the scientific community. Now, two papers out in Science refute this arsenic-for-phosphorous claim.

Mono Lake is a promising place to look for extremophilic behavior. The waters there have high levels of arsenic and a productive ecosystem based on brine shrimp that thrives despite arsenic's poisonous nature. The temptation to see just how well-adjusted that ecosystem is to elemental arsenic is understandable. Felisa Wolfe-Simon led a research team to investigate this possibility and claimed to have found the bacteria GFAJ-1 substituting phosphorous for arsenic. The claim, more specifically, indicated that the bacteria was able to incorporate small amounts of arsenic in place of phosphorous in the bacteria's DNA and do so successfully, making it the first known lifeform on Earth to do this. The results were published in Science in December of 2010 and quickly caused consternation among some in the scientific community.

The Tardigrades: Earth's Toughest Lifeform?

Photo courtesy of http://www.sciencephoto.com

Hank Green gives us a quick introduction to the Tardigrades, a kind of extremophile. Tardigrades, sometimes known as "Water Bears" or "Moss Piglets" live in water, have eight legs, feed on moss, and are very small - microscopic, in fact. They live worldwide in many different altitudes and environments including various levels of the ocean. They are known as very tough organisms, despite being so tiny. NASA sent these guys into space just to see if their reputations for toughness bear out. It turns out that Tardigrades are, unusually, one of the toughest organisms on Earth.

They were sent into space and tested in two controlled sets of populations. The first water bear population set was exposed to both the vacuum of space and to the solar radiation emitted by the sun. The second population set was exposed to just the vacuum of space and NOT the harmful solar radiation. Many of the Tardigrades survived the exposure and the trip back to Earth, where some of them even reproduced after their experience.

One of the implications of this experiment informs us on the possibilities of Panspermia. Panspermia is the idea that life can be seeded onto a dead world, perhaps naturally...that life is tough enough to survive a journey from one planetary body to another in a solar system. The Tardigrades's experience in space certainly opens up the possibility of a Panspermiated Solar System. if they can survive this, then what else is possible? Check out Hank Green's video below. After the video, check out some gnarly Water Bear photography #WaterBearPorn

Isn't he cute? Photo courtesy of http://www.sciencephoto.com