Biohistory Jyournal, Spring, 2004

Research: Index > Primitive life forms and the form of the earth

The time of environment Primitive life forms and the form of the earth

Akihiko Yamagishi, Department of Molecular Biology, Tokyo University of Pharmacy and Life Science

The earth was born about 4.6 billion years ago in a magma state. Heat was emitted into space, primitive oceans were formed, and organic compounds accumulated in it over a long period of time. Likely, the first organisms were heterotrophic creatures created in the soup of these organic compounds. Then, before the limited amount of organic compounds could be consumed completely, living creatures using the energy from inorganic compounds to create organic material were born. These are called chemotrophs. These chemotrophs still exist today near the hydrothermal vents on the sea bottom, which produce a continual supply of hydrogen sulfide and other inorganic compounds.     Research into the chromosome DNA sequence from samples taken from holes dug at excavation sites on the seabed at the crater of the Suiyo seamount deep in the ocean reveals that most of the creatures living there are new. It is necessary to cultivate these creatures to determine which living creatures actually exist here. We are moving ahead with plans to create devices in the laboratory to recreate the environment of a seabed hydrothermal system (400 ¡C, 300 atm).     We hope to propagate microorganisms that have never been cultivated before, thereby gaining clues for the understanding of primitive creatures.

Location of the Suiyo seamount     One of the seven seamounts in the Shichiyo seamount chain, which ranges from Nichiyo to Doyo, the Suiyo seamount is located to the west of the Ogasawara islands. The active caldera at the summit of the seamount spouts hot water.

Near the hydrothermal vents on the sea bottom     Beneath the volcanic mountains on the seabed, beyond the reach of the light energy of sun, there is an ecological system relying on the organic compounds created by chemotrophs.

How are we to understand primitive creatures and the global environment in which they lived? We experimentally created the enzyme (protein) that these creatures are thought to have had and studied its characteristics. 1. It has been understood from creating an evolutionary tree of the genes of 3-isopropylmalate dehydrogenase (IPMDH) in creatures that exist today that aerobic Hyperthermophilic archaea, sulfolobus tokodaii, is the closest creature to the root of the tree--in other words, the closest common ancestor. 2. We created IPMDH with a modified amino acid to approach the sequence of the common ancestor we anticipated for the bacteria's IPMDH from the evolutionary tree. 3. We compared the thermostability of the altered IPMDH with the original IPMDH.     In this experiment, there was an increase of thermostability in five of the seven IPMDH samples altered to more closely resemble those thought to have been that of the amino acid ancestor. This suggests that the common ancestor of all of the organisms were raised in heat greater than today's hyperthermophilic archaea.

We determined the targeted amino acid (white dot) from the IPMDH amino acid sequence in sulfolobus tokodaii, created an IPMDH that had been modified to the amino acid of the ancestor (yellow dot), and examined the changes in the thermostability. The figures represent the temperature change (¡C) compared to the IPMDH thermostability of the original sulfolobus tokodaii. These are arranged in the order of the greatest thermostability. A = Alanine, G = Glycine, F = Phenylalanine, I = Isoleucine, K = Lysine, L = Leucine, M = Methionine, P = Proline, R = Arginine, S = Serine, Y = Tyrosine

Akihiko Yamagishi     Received a Ph.D. from the Graduate School of Science at the University of Tokyo. He served as a postdoctoral research fellow at the Japan Society for the Promotion of Science, an assistant at the Graduate School of Sciences at the University of Tokyo, a doctoral fellow at the University of California at Berkeley, Carnegie and an assistant at the Department of Science of the Tokyo Institute of Technology (in what is now the Department of Bioscience and Biotechnology). He is currently an Associate Professor in Cellular Biochemistry in the Department of Molecular Biology at the Tokyo University of Pharmacy and Life Science.

		The vague form created by the environment: Podostemaceae

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