Prochlorococcus and the Origin of Life

June 20, 2008 by Dr. Mc.

Last week NPR helped
celebrate the 20th anniversary of the discovery of prochlorococcus, the smallest
known organism to produce food by photosynthesis. And since it is responsible
for about 50% of photosynthesis, it is arguably the most abundant. As far as we
know, this guy is rock bottom of the food chain, being referred to as an
obligate phototroph. Let’s take that one at a time: obligate (essential)
phototroph (organism that produces its own food via photosynthesis). It is
essential for life on earth, at least as we know it, and it today produces about
1/5th of our oxygen. Though it contains only 2,000 genes, some scientists argue
that it is not the earliest form of life on earth, saying that its ancestor had to be a more
complicated cousin. Another interesting point, it only has about 60% of its
genes in common with its nearest known relatives. That’s less than you have in
common with a fish.

Allow me to think out load about this: All organisms must
survive by processing organic compounds that only come from organisms. In the
absence of all other organisms, the first organism must have produced its own
food, because by definition there would be no other source. The simplest known
food-producer, upon which we are dependent, requires 2.000 genes of DNA code,
and it is suspected of originating from something more complex. Also, it seems
that as we go "down" the "tree of life," the organisms are in many cases more
distinct from each other, not less. I don’t see us getting any closer to an
accidental (random) origin of life.

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