Deep Life Is Right at Home in Total Darkness
It seems every year scientists find organisms thriving in environments thought too inhospitable for life. A new word was coined for these organisms: extremophiles – lovers of the extreme. Two recent discoveries push the envelope of extreme environments almost to the deep limit.
- Pressurized fish: The bottoms of the deep ocean trenches of the Pacific have never been photographed – till now. It took Oceanlab, a robotic submarine, five hours just to reach bottom – 7700 meters down, almost five miles below the surface. It is completely dark down there. The pressure is so high – 8000 tonnes per square meter – it would be like 1600 elephants piled on a car. The temperature is freezing. Imagine the astonishment of scientists finding schools of snailfish happily feeding in social groups. The picture is there on Science Daily.
The director of Oceanlab said, “It’s incredible…. We thought the deepest fishes would be motionless, solitary, fragile individuals eking out an existence in a food-sparse environment,” but they were agile, not fragile. “The images show groups that are sociable and active – possibly even families – feeding on little shrimp, yet living in one of the most extreme environments on Earth.”
- Gold strike: Science Daily also reported one-of-a-kind microorganisms living in a gold mine 1.74 miles below ground. These organisms are not part of a food chain. The subsist entirely on hydrogen and sulfate produced by radioactive decay of uranium. They live in total darkness, with no oxygen. The genome of this microbe shows that it shares many genes with Archaea, many species of which also live in extreme environments like hot springs. This species appears to live in solitary confinement in the crust of the earth where no nutrients from the biosphere reach it.
The microbe was named Desulforudis audaxviator. Its genome was found to be a superset of the raw essentials. It has 2,157 protein-coding genes, more than the 1500-some-odd genes of streamlined bacteria. This surprised the scientists: “The genome was not as streamlined as might be expected of an organism living in what is presumably a very stable environment.” It “contained everything needed for the organism to sustain an independent existence and reproduce, including the ability to incorporate the elements necessary for life from inorganic sources, move freely, and protect itself from viruses, harsh conditions, and nutrient-poor periods by becoming a spore.” Apparently this is the only species living in the habitat of a deep gold mine in South Africa.
Scientists immediately latched onto possible astrobiological ramifications of the second story:
“One question that has arisen when considering the capacity of other planets to support life is whether organisms can exist independently, without access even to the sun,”says [Dylan] Chivian [Berkeley Labs]. “The answer is yes, and here’s the proof. It’s sort of philosophically exciting to know that everything necessary for life can be packed into a single genome.”
Yet no one was suggesting these microbes originated there on their own. They likely became adapted to the dark depths from progenitors on the surface having the full complement of genetic information required for life. “During its long journey to the extreme depths, evolution has equipped the versatile spelunker with genes – many of them shared with archaea, members of a separate domain of life unrelated to bacteria – that allow it to cope with a range of different conditions, including the ability to fix nitrogen directly from elemental nitrogen in the environment.”
Yet if the microbe was like a spelunker, it took the equipment with it from the surface and jettisoned some unnecessary cargo along the way. That makes this a case of devolution, not evolution. Natural selection could have intensified existing genes that work in the environment, and removed the useless ones. If astrobiologists are to use this earthly example as a model for self-sustaining life on other planets, the lesson is that complex life with large genomes is required before streamlined editions adapted to extreme habitats could survive. That must be the deduction unless they could prove D. audaxviator was the original life form from which all the biosphere evolved – a hypothesis they would probably not support, given the common evolutionary assumption that life originated in earth’s oceans.
“Evolution has equipped the versatile spelunker with genes….” Oh, please. No fairy tales while we are trying to appreciate the wonders of creation. It’s like stocking fool’s gold in a gold mine, or dousing a deep-battered fish dinner with ipecac.