Discussion and news about the modern effort to understand the nature of life on Earth, finding planets around other stars, and the search for life elsewhere in the universe

Wednesday, October 13, 2010

We salute you...

Bacteria. Asexual lords and masters of the planet. An extraordinary and fascinating piece of work has popped up that indicates a form of bacterial networking that inches this sentiment even further along from the figurative to the literal. In a study of the bacterium S. oneidensis (an organism capable of actually reducing, or 'breathing', heavy metals) El-Naggar and colleagues find that when stressed these microscopic lifeforms can grow so-called bacterial nano-wires. These incredibly thin protrusions - really stalks of protein - exhibit electrical conductivity. This work builds on earlier studies that also hinted as this property.
They're no piece of copper when it comes to transporting electrons, but they seem to be on a par with semi-conductor materials.

The experimental work is quite wonderful, and shows that colonies of S. oneidensis may actually link themselves together in a remarkable type of electrical grid. Why do they do this, are they just engaged in some form of microbial Facebook? The answer may be one of survival. The respiration of S. oneidensis is acutely dependent on the ability to off-load unwanted electrons - performing chemical reduction on anything able to accept the electrons. If a single individual can't dump its electrons it dies. So, if you can send out nano-wires and make an electrical connection with someone else you can pass off your particles - and if that individual can't accept them it can simply re-route the current further along the network, until eventually it gets slurped up. It's an incredible ability, the colony comes to the rescue of the few, and nobody has to get out of their armchair.

As the researchers point out, beyond enabling the group to respire and survive, bacterial nano-wires open up a whole new avenue of fast communication - much speedier than chemical signaling. One cannot help but see a parallel between this situation and the web of neurons and electrical synapses lurking between our own ears. The more we learn about life on Earth, the more blurred the line becomes between 'simple' and 'complex' life, and the more archaic that classification appears.


kurt9 said...

I've a question for you with regards to exobiology.

If the Eukaryotes had never formed, would the prokaryotic photosynthetic bacteria been able to, on their own, to create as Oxygen-rich atmosphere as Earth has today?

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Caleb Scharf said...

kurt9, an excellent question. I don't have quantitative details to hand (perhaps someone out there can comment?), but my understanding is that 2-2.5 billion years ago with the rapid rise in atmospheric oxygen from photosynthetic microbial life (e.g. cyanobacteria) the O2 levels did get pretty close to our present-day levels. This was well before multi-cellular life.

I don't actually know what the partitioning is for O2 sources on the *modern* Earth - i.e. between prokaryotes vs. eukaryotes.

kurt9 said...

I read Nick lane's "Power, Sex, and Suicide" about the story of mitochondria. His description of the endosymbiotic theory and, especially, the hydrogen hypothesis, has me convince that the emergence of the Eukaryote is so unlikely event that the Earth is the only example of it in this galaxy. If this is true and Eukaryotes are necessary to get the free Oxygen partial pressure for us to breath, then there are not going to be any habitable planets for us even if we get FTL capability. It would also be the answer for the "Great Silence" at the very least.

Eniac said...

On the Wikipedia page on the oxygen cycle it says

Photosynthesizing organisms include the plant life of the land areas as well as the phytoplankton of the oceans. The tiny marine cyanobacterium Prochlorococcus was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean.[1]

It also gives numbers for land and ocean based photosynthesis, with land a little (~20%) higher than ocean. Thus, it would seem, this single organism alone accounts for 20-30% of all photosynthesis.

Eniac said...

This is an excellent article. It makes me wonder if our brains could be a lot better if they were wired with electron conducting protein chains like these bacteria use, rather than with the comparably slow and bulky axons we actually use.

Eniac said...

Kurt9: Just like endosymbiosis, multicellular life has evolved independently many times. Some prokaryotes even form multicellular organisms (myxobacteria, for example).

I think there is therefore no basis in the belief that the evolution of eukaryotes is unique, nor that it is necessary for "complex" life.

Caleb Scharf said...

I'd be inclined to agree. Take a look at:

for another example of complex symbiosis and 'microbial' life that isn't so 'micro'.

kurt9 said...

The astronomical test of these ideas will be the detection of free Oxygen atmospheres of exoplanets. A free Oxygen atmosphere indicates photosynthetic life on that planet, whether it be prokaryotic or Eukaryotic. Failure to detect Oxygen atmospheres will suggest that life is rare.

It seems to me that the Terrestrial Planet Finder or some other proposed apace-based instrument should be able to analyze exo-planet atmospheres for those within, say, 100 light years.

Unfortunately, it will be another 10 years before any of this gets done.

Eniac said...

If indeed astronomical observation shows no oxygen, and by (somewhat shaky) implication that life is rare, of all the possible culprits suspicion should then clearly fall on abiogenesis. Unlike DNA and proteins, mitochondrial endosymbiosis, photosynthesis, migration onto land, use of tools, and all the other supposedly critical stages of our evolution, this one is really, truly special: We cannot easily explain it in terms of evolution, because there is no reproducing organism to begin with. The best we can do is postulate some sort of bootstrapping mechanism, with pre-evolutionary complex chemistry, autocatalysis, hypercycles, and the like. Models that are interesting and probably hold a kernel of truth, but with insufficient data to even pick one, much less to determine whether their realization is commonplace or a "once in the universe" event.

Eniac said...

I love the giant archeon. Here is another giant, relatively speaking: http://en.wikipedia.org/wiki/Thiomargarita_namibiensis
Almost a millimeter big, and making anyone look silly who claims cells need mitochondria to be big.

kurt9 said...

Cells can be big, but they're necessarily limited in capability without mitochondria.


This is what I've been saying all along. I think Nick Lane is spot on about this. This is also why I think we're alone (in this galaxy).

Look at the bright side. We get an FTL and all of that real estate is our's. You can't beat that with a stick.

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Eniac said...

kurt9: Statements like "*only* mitochondria can do this", or "Even aliens will need mitochondria" make me very uncomfortable.

What Lane hypothesizes in this Nature Hypothesis paper is that bigger genomes need more energy. This is very reasonable. But then he somehow leaps to the conclusion (or maybe he doesn't and you do; I have no access to that Nature paper) that mitochondria are a unique and rare way to provide this energy.

This leap of faith is just simply baseless. Are there not other ways to supply more energy? How can you exclude all of them? What about chloroplasts? They have replaced mitochondria completely for energy production in most plants. Where is the uniqueness of mitochondria?

The best you can say is that, as far as we know, mitchondria were the *first* endosymbiont to provide cellular energy, but that does not at all mean they are the *only* one. They aren't, in fact, as is demonstrated by the chloroplast.

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