Posted by jlwile on December 3, 2010
“NASA Finds New Life Form” is the headline on the Fox News website. The article says:
NASA has discovered a new life form, a bacteria called GFAJ-1 that is unlike anything currently living in planet Earth. It’s capable of using arsenic to build its DNA, RNA, proteins, and cell membranes. This changes everything…NASA is saying that this is “life as we do not know it”. The reason is that all life on Earth is made of six components: Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Every being, from the smallest amoeba to the largest whale, share the same life stream. Our DNA blocks are all the same. That was true until today.
While the NASA team has done something quite amazing, Fox News and other similar outlets have really over-hyped it. Not surprisingly, to get the real story, you must read the scientific article, which is groundbreaking indeed, but not in the way that the standard media outlets are saying.
The NASA team was studying organisms that live in the sediments of Mono Lake in eastern California. This lake has no rivers to carry its water away, so the only way water can leave the lake is by evaporation. As a result, any dissolved solids that are washed into the lake by rain stay there pretty much for as long as the lake is there. This has resulted in a saltwater lake that is roughly three times saltier than the ocean. It is also rich in other chemicals, such as carbonates, phosphorus, sulfur, and arsenic.
In some ways, it is amazing that anything can live in the lake given that kind of chemical makeup. Nevertheless, bacteria, shrimp, some algae, and flies (in their first two stages of development) live in the salty, chemical-laden water. NASA is interested in life that can exist in such extreme conditions, because it is interested in finding life in other parts of the universe. The earth is perfectly designed for life, but it is unlikely that there will be many (or any) other wonderfully-designed planets out there. Thus, many who are interested in finding life on other planets think that the best bet for extraterrestrial life rests in life forms that can survive extreme conditions.
The inhabitants of Mono Lake represent life in extreme conditions, so they are of interest to groups who are looking for life elsewhere in the universe. One question the NASA team wanted to answer was whether or not any of these extreme-loving organisms could be coaxed to live in even more extreme conditions. Thus, they took samples of bacteria found in the sediments and started trying to get them to grow in artificial environments where the arsenic levels were higher than those found in the lake.
Arsenic is poisonous to most forms of life. The reason is that all organisms on the planet use phosphorus in their chemistry. The backbone of DNA, for example, is compose of the sugar deoxyribose and a phosphorus/oxygen ion called phosphate (PO43-). Well, if you look at the Periodic Table of Elements, you will find that arsenic is in the same column as phosphorus, and it is one row below. As any freshman chemistry student should be able to tell you, then, arsenic and phosphorus have very similar chemical properties. For example, arsenic can also form an ion with oxygen, and not surprisingly, it is called arsenate (AsO43-).
Well, the chemistry between arsenic and phosphorus is similar enough that when most organisms take in arsenic, it gets used in their biochemistry as if it were phosphorus. Unfortunately, however, the chemistry of arsenic is not identical to that of phosphorus, and the subtle differences between the two are enough to wreak havoc on the biochemical processes that run most organisms. As a result, most organisms will die if they take in too much arsenic. Nevertheless, NASA found a bacterium, a member of the salt-loving family Halomonadaceae, that could incorporate a large amount of arsenic into its own biochemistry and not be killed as a result.
In the experiments, they grew some of the bacteria in cultures that had plenty of phosphorus. Those bacteria reproduced quickly and thrived. They grew other bacteria from the same species in cultures that were rich in arsenic and poor in phosphorus. Those bacteria were able to survive, but they did not thrive like the ones that were given plenty of phosphorus. Instead, they reproduced more slowly, and they were larger than those that were given plenty of phosphorus. Chemical analysis of these larger bacteria showed that they seemed to be incorporating arsenic into their biochemistry without dying. Indeed, arsenate seemed to have even been used in place of phosphate in parts of the DNA.
Now this is all ground-breaking stuff. In the end, arsenic was thought to be too unstable to be successfully incorporated into an organism’s biochemistry. The fact that this particular bacterium can do it demonstrates the scientific consensus is wrong on that point. That, in and of itself, is incredibly important. However, unlike Fox News and other outlets have stated, this is definitely not “unlike anything currently living in planet Earth.” It is a current inhabitant of the planet, and under normal conditions, it behaves like any other extreme-condition-loving bacterium. It uses the same basic elements (including phosphorus) that all other organisms use. The amazing part is if you give the bacterium no choice, it will incorporate arsenic into its biochemistry without dying. That changes the bacterium, of course, making it larger. Also, it seems to harm the bacterium to some extent, as it cannot reproduce as effectively anymore. Nevertheless, the bacterium doesn’t die, which is what you would expect.
So is this ground-breaking? Yes, of course. Is it a new life form? No, of course not. It is a bacterium that can live in extreme conditions, like many other bacteria that live on this planet. However, it does seem to have an ability that is quite special. It can use arsenic instead of phosphorus if it has no choice. That’s something no one has ever seen before, but it is far from a new life form!
Now, of course, because I am a Star Trek fan, this brings to mind one of my five favorite episodes from the original series. In the episode called “Devil in the Dark,” Captain Kirk, Mr. Spock, and Dr. McCoy encounter a strange creature whose chemistry is built on silicon rather than carbon. All organic compounds on earth are based on carbon, but because silicon is in the same column as carbon on the Periodic Table of Elements, it could hypothetically replace the carbon in organic compounds, forming a silicon-based life form. Indeed, the team finds such a life form, which calls itself a “Horta.” This produces a lot of wonderful interaction between Kirk, Spock, and McCoy, and my favorite comes when the team realizes the Horta is injured. Kirk tells McCoy to help the Horta, which leads to:
McCoy: You can’t be serious. That thing is virtually made out of stone!
Kirk: Help it. Treat it.
McCoy: I’m a doctor, not a bricklayer.
Kirk: You’re a healer. There’s a patient. That’s an order.
While NASA didn’t find something similar to a Horta, it did show that the current scientific consensus on arsenic in biochemical systems is at least partly wrong. While that’s not as grand as what many news outlets are saying, it could be the most important scientific discovery of this year.