On Nobel Intent, minimal genomes are being discussed. The organisms in question are endosymbionts, free-floating cells that take up residence inside of animal cells, forming a symbiotic relationship. Apparently some of these species have extremely tiny genomes:

[…] there’s a second paper on the endosymbiont in a related species, a psyllid, that makes the first genome look big. In this case, the bacterial genome has been whittled down into an extremely gene-rich 166 Kilobases with 182 genes. Over 97 percent of that genome codes for something; in fact, nearly a full percent of it codes for parts of two genes at once.

What do I take away from this? Well, aside from general scientific interest, I think that the successful existence of minimal genome organisms in nature shows us how low of a complexity threshold will be necessary to engineer green goo. That is, artificial variants of natural organisms with much greater physical performance, such that they will be capable of entirely displacing the original population. If other organisms are dependent on the displaced organism for food or some other reason, their disappearance could lead to catastrophic ecological collapse much more rapidly than scientifically questionable anthropogenic global warming.

In this Wired article on green goo:

In its report, published on July 8, the Action Group on Erosion, Technology and Concentration said the risks from green goo demand the most urgent foresight and caution. “With nanobiotech, researchers have the power to create completely new organisms that have never existed on Earth,” said the ETC release accompanying its report.

It’s a new one for some players. “I haven’t heard of this concern anywhere else, I mean anywhere else,” said Christine Peterson, president of the Foresight Institute, a nonprofit dedicated to accelerating the potential benefits and anticipating potential risks of nanotechnology. “I think it’s because people are already aware of the issues of biotech. I’m not sure there’s an additional issue here.”

Christine wants to avoid an irrational aversion to Drexlerian nanotechnology stemming from concerns about green goo, similar to the irrational aversion to nanotech brought about by the fear of free-floating grey goo. However, there is great warrant for fear in this case. Today, designing and manufacturing an artificial life form has already been done at least once - for an artificial virus. We have created life. I predict we will create artificial bacteria by 2010, not just by writing their genomes, but actually by building them from scratch. It will cost millions and maybe a dozen Ph.Ds, but the difficulty threshold will drop like a stone.

By 2020, creating cybernetic microorganisms capable of entirely displacing their biological equivalents will become feasible in a university lab, with minimal funding. Then the potential problems will begin. Artificial viruses, bacteria, photoplankton, algae, even krill or insects could quickly be produced in great numbers before the end of the second decade of this century, which would then go on to self-replicate beyond our control. This scenario is not only conceivable, but probable - it only takes one successful self-replicator to create a major hassle. If it’s a self-replicator that throws a wrench into human biology in particular, it could kill every person on earth in the time it takes to spread globally.

Because artificial organisms will have the potential for superior performance, they could spread much faster than natural species, while being capable of surviving in a much wider range of niches. Based on the principles of evolvable hardware, we can produce artificial organisms that evolve thousands or millions of times faster than their natural counterparts. Imagine an artificial chloroplast that jumps from cell to cell, plant to plant, continent to continent, rendering their hosts incapable of photosynthesis.

One of the only useful conceivable countermeasures would be to have obedient artificial microorganisms already fully distributed in the background environment - “blue goo” - so that we can instruct them to attack the green goo should it become a problem. Another would be successfully building Friendly AI, which could take care of the problem better than we ever could. A useful backup measure would be to launch self-sustaining space colonies, a la Lifeboat Foundation.